Move skdiff tool and add to gn build.

I really wanted this today, so I got it working again.

Change-Id: I1a37d48d4806198b55c59d1df5ff15a03500195f
Reviewed-on: https://skia-review.googlesource.com/3383
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>

8 files changed, 2301 insertions, 0 deletions

diff --git a/tools/skdiff/skdiff.cpp b/tools/skdiff/skdiff.cpp
new file mode 100644
index 0000000000..ae6d72cd7a
--- /dev/null
+++ b/tools/skdiff/skdiff.cpp
@@ -0,0 +1,228 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "skdiff.h"
+#include "SkBitmap.h"
+#include "SkColor.h"
+#include "SkColorPriv.h"
+#include "SkTypes.h"
+
+/*static*/ char const * const DiffRecord::ResultNames[DiffRecord::kResultCount] = {
+    "EqualBits",
+    "EqualPixels",
+    "DifferentPixels",
+    "DifferentSizes",
+    "CouldNotCompare",
+    "Unknown",
+};
+
+DiffRecord::Result DiffRecord::getResultByName(const char *name) {
+    for (int result = 0; result < DiffRecord::kResultCount; ++result) {
+        if (0 == strcmp(DiffRecord::ResultNames[result], name)) {
+            return static_cast<DiffRecord::Result>(result);
+        }
+    }
+    return DiffRecord::kResultCount;
+}
+
+static char const * const ResultDescriptions[DiffRecord::kResultCount] = {
+    "contain exactly the same bits",
+    "contain the same pixel values, but not the same bits",
+    "have identical dimensions but some differing pixels",
+    "have differing dimensions",
+    "could not be compared",
+    "not compared yet",
+};
+
+const char* DiffRecord::getResultDescription(DiffRecord::Result result) {
+    return ResultDescriptions[result];
+}
+
+/*static*/ char const * const DiffResource::StatusNames[DiffResource::kStatusCount] = {
+    "Decoded",
+    "CouldNotDecode",
+
+    "Read",
+    "CouldNotRead",
+
+    "Exists",
+    "DoesNotExist",
+
+    "Specified",
+    "Unspecified",
+
+    "Unknown",
+};
+
+DiffResource::Status DiffResource::getStatusByName(const char *name) {
+    for (int status = 0; status < DiffResource::kStatusCount; ++status) {
+        if (0 == strcmp(DiffResource::StatusNames[status], name)) {
+            return static_cast<DiffResource::Status>(status);
+        }
+    }
+    return DiffResource::kStatusCount;
+}
+
+static char const * const StatusDescriptions[DiffResource::kStatusCount] = {
+    "decoded",
+    "could not be decoded",
+
+    "read",
+    "could not be read",
+
+    "found",
+    "not found",
+
+    "specified",
+    "unspecified",
+
+    "unknown",
+};
+
+const char* DiffResource::getStatusDescription(DiffResource::Status status) {
+    return StatusDescriptions[status];
+}
+
+bool DiffResource::isStatusFailed(DiffResource::Status status) {
+    return DiffResource::kCouldNotDecode_Status == status ||
+           DiffResource::kCouldNotRead_Status == status ||
+           DiffResource::kDoesNotExist_Status == status ||
+           DiffResource::kUnspecified_Status == status ||
+           DiffResource::kUnknown_Status == status;
+}
+
+bool DiffResource::getMatchingStatuses(char* selector, bool statuses[kStatusCount]) {
+    if (!strcmp(selector, "any")) {
+        for (int statusIndex = 0; statusIndex < kStatusCount; ++statusIndex) {
+            statuses[statusIndex] = true;
+        }
+        return true;
+    }
+
+    for (int statusIndex = 0; statusIndex < kStatusCount; ++statusIndex) {
+        statuses[statusIndex] = false;
+    }
+
+    static const char kDelimiterChar = ',';
+    bool understood = true;
+    while (true) {
+        char* delimiterPtr = strchr(selector, kDelimiterChar);
+
+        if (delimiterPtr) {
+            *delimiterPtr = '\0';
+        }
+
+        if (!strcmp(selector, "failed")) {
+            for (int statusIndex = 0; statusIndex < kStatusCount; ++statusIndex) {
+                Status status = static_cast<Status>(statusIndex);
+                statuses[statusIndex] |= isStatusFailed(status);
+            }
+        } else {
+            Status status = getStatusByName(selector);
+            if (status == kStatusCount) {
+                understood = false;
+            } else {
+                statuses[status] = true;
+            }
+        }
+
+        if (!delimiterPtr) {
+            break;
+        }
+
+        *delimiterPtr = kDelimiterChar;
+        selector = delimiterPtr + 1;
+    }
+    return understood;
+}
+
+static inline bool colors_match_thresholded(SkPMColor c0, SkPMColor c1, const int threshold) {
+    int da = SkGetPackedA32(c0) - SkGetPackedA32(c1);
+    int dr = SkGetPackedR32(c0) - SkGetPackedR32(c1);
+    int dg = SkGetPackedG32(c0) - SkGetPackedG32(c1);
+    int db = SkGetPackedB32(c0) - SkGetPackedB32(c1);
+
+    return ((SkAbs32(da) <= threshold) &&
+            (SkAbs32(dr) <= threshold) &&
+            (SkAbs32(dg) <= threshold) &&
+            (SkAbs32(db) <= threshold));
+}
+
+const SkPMColor PMCOLOR_WHITE = SkPreMultiplyColor(SK_ColorWHITE);
+const SkPMColor PMCOLOR_BLACK = SkPreMultiplyColor(SK_ColorBLACK);
+
+void compute_diff(DiffRecord* dr, DiffMetricProc diffFunction, const int colorThreshold) {
+    const int w = dr->fComparison.fBitmap.width();
+    const int h = dr->fComparison.fBitmap.height();
+    if (w != dr->fBase.fBitmap.width() || h != dr->fBase.fBitmap.height()) {
+        dr->fResult = DiffRecord::kDifferentSizes_Result;
+        return;
+    }
+
+    SkAutoLockPixels alpDiff(dr->fDifference.fBitmap);
+    SkAutoLockPixels alpWhite(dr->fWhite.fBitmap);
+    int mismatchedPixels = 0;
+    int totalMismatchA = 0;
+    int totalMismatchR = 0;
+    int totalMismatchG = 0;
+    int totalMismatchB = 0;
+
+    // Accumulate fractionally different pixels, then divide out
+    // # of pixels at the end.
+    dr->fWeightedFraction = 0;
+    for (int y = 0; y < h; y++) {
+        for (int x = 0; x < w; x++) {
+            SkPMColor c0 = *dr->fBase.fBitmap.getAddr32(x, y);
+            SkPMColor c1 = *dr->fComparison.fBitmap.getAddr32(x, y);
+            SkPMColor outputDifference = diffFunction(c0, c1);
+            uint32_t thisA = SkAbs32(SkGetPackedA32(c0) - SkGetPackedA32(c1));
+            uint32_t thisR = SkAbs32(SkGetPackedR32(c0) - SkGetPackedR32(c1));
+            uint32_t thisG = SkAbs32(SkGetPackedG32(c0) - SkGetPackedG32(c1));
+            uint32_t thisB = SkAbs32(SkGetPackedB32(c0) - SkGetPackedB32(c1));
+            totalMismatchA += thisA;
+            totalMismatchR += thisR;
+            totalMismatchG += thisG;
+            totalMismatchB += thisB;
+            // In HSV, value is defined as max RGB component.
+            int value = MAX3(thisR, thisG, thisB);
+            dr->fWeightedFraction += ((float) value) / 255;
+            if (thisA > dr->fMaxMismatchA) {
+                dr->fMaxMismatchA = thisA;
+            }
+            if (thisR > dr->fMaxMismatchR) {
+                dr->fMaxMismatchR = thisR;
+            }
+            if (thisG > dr->fMaxMismatchG) {
+                dr->fMaxMismatchG = thisG;
+            }
+            if (thisB > dr->fMaxMismatchB) {
+                dr->fMaxMismatchB = thisB;
+            }
+            if (!colors_match_thresholded(c0, c1, colorThreshold)) {
+                mismatchedPixels++;
+                *dr->fDifference.fBitmap.getAddr32(x, y) = outputDifference;
+                *dr->fWhite.fBitmap.getAddr32(x, y) = PMCOLOR_WHITE;
+            } else {
+                *dr->fDifference.fBitmap.getAddr32(x, y) = 0;
+                *dr->fWhite.fBitmap.getAddr32(x, y) = PMCOLOR_BLACK;
+            }
+        }
+    }
+    if (0 == mismatchedPixels) {
+        dr->fResult = DiffRecord::kEqualPixels_Result;
+        return;
+    }
+    dr->fResult = DiffRecord::kDifferentPixels_Result;
+    int pixelCount = w * h;
+    dr->fFractionDifference = ((float) mismatchedPixels) / pixelCount;
+    dr->fWeightedFraction /= pixelCount;
+    dr->fTotalMismatchA = totalMismatchA;
+    dr->fAverageMismatchA = ((float) totalMismatchA) / pixelCount;
+    dr->fAverageMismatchR = ((float) totalMismatchR) / pixelCount;
+    dr->fAverageMismatchG = ((float) totalMismatchG) / pixelCount;
+    dr->fAverageMismatchB = ((float) totalMismatchB) / pixelCount;
+}
diff --git a/tools/skdiff/skdiff.h b/tools/skdiff/skdiff.h
new file mode 100644
index 0000000000..6bdaadc28d
--- /dev/null
+++ b/tools/skdiff/skdiff.h
@@ -0,0 +1,272 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef skdiff_DEFINED
+#define skdiff_DEFINED
+
+#include "SkBitmap.h"
+#include "SkColor.h"
+#include "SkColorPriv.h"
+#include "SkString.h"
+#include "../private/SkTDArray.h"
+
+#if defined(SK_BUILD_FOR_WIN32)
+    #define PATH_DIV_STR "\\"
+    #define PATH_DIV_CHAR '\\'
+#else
+    #define PATH_DIV_STR "/"
+    #define PATH_DIV_CHAR '/'
+#endif
+
+#define MAX2(a,b) (((b) < (a)) ? (a) : (b))
+#define MAX3(a,b,c) (((b) < (a)) ? MAX2((a), (c)) : MAX2((b), (c)))
+
+
+struct DiffResource {
+    enum Status {
+        /** The resource was specified, exists, read, and decoded. */
+        kDecoded_Status,
+        /** The resource was specified, exists, read, but could not be decoded. */
+        kCouldNotDecode_Status,
+
+        /** The resource was specified, exists, and read. */
+        kRead_Status,
+        /** The resource was specified, exists, but could not be read. */
+        kCouldNotRead_Status,
+
+        /** The resource was specified and exists. */
+        kExists_Status,
+        /** The resource was specified, but does not exist. */
+        kDoesNotExist_Status,
+
+        /** The resource was specified. */
+        kSpecified_Status,
+        /** The resource was not specified. */
+        kUnspecified_Status,
+
+        /** Nothing is yet known about the resource. */
+        kUnknown_Status,
+
+        /** NOT A VALID VALUE -- used to set up arrays and to represent an unknown value. */
+        kStatusCount
+    };
+    static char const * const StatusNames[DiffResource::kStatusCount];
+
+    /** Returns the Status with this name.
+     *  If there is no Status with this name, returns kStatusCount.
+     */
+    static Status getStatusByName(const char *name);
+
+    /** Returns a text description of the given Status type. */
+    static const char *getStatusDescription(Status status);
+
+    /** Returns true if the Status indicates some kind of failure. */
+    static bool isStatusFailed(Status status);
+
+    /** Sets statuses[i] if it is implied by selector, unsets it if not.
+     *  Selector may be a comma delimited list of status names, "any", or "failed".
+     *  Returns true if the selector was entirely understood, false otherwise.
+     */
+    static bool getMatchingStatuses(char* selector, bool statuses[kStatusCount]);
+
+    DiffResource() : fFilename(), fFullPath(), fBitmap(), fStatus(kUnknown_Status) { }
+
+    /** If isEmpty() indicates no filename available. */
+    SkString fFilename;
+    /** If isEmpty() indicates no path available. */
+    SkString fFullPath;
+    /** If empty() indicates the bitmap could not be created. */
+    SkBitmap fBitmap;
+    Status fStatus;
+};
+
+struct DiffRecord {
+
+    // Result of comparison for each pair of files.
+    // Listed from "better" to "worse", for sorting of results.
+    enum Result {
+        kEqualBits_Result,
+        kEqualPixels_Result,
+        kDifferentPixels_Result,
+        kDifferentSizes_Result,
+        kCouldNotCompare_Result,
+        kUnknown_Result,
+
+        kResultCount  // NOT A VALID VALUE--used to set up arrays. Must be last.
+    };
+    static char const * const ResultNames[DiffRecord::kResultCount];
+
+    /** Returns the Result with this name.
+     *  If there is no Result with this name, returns kResultCount.
+     */
+    static Result getResultByName(const char *name);
+
+    /** Returns a text description of the given Result type. */
+    static const char *getResultDescription(Result result);
+
+    DiffRecord()
+        : fBase()
+        , fComparison()
+        , fDifference()
+        , fWhite()
+        , fFractionDifference(0)
+        , fWeightedFraction(0)
+        , fAverageMismatchA(0)
+        , fAverageMismatchR(0)
+        , fAverageMismatchG(0)
+        , fAverageMismatchB(0)
+        , fTotalMismatchA(0)
+        , fMaxMismatchA(0)
+        , fMaxMismatchR(0)
+        , fMaxMismatchG(0)
+        , fMaxMismatchB(0)
+        , fResult(kUnknown_Result) {
+    }
+
+    DiffResource fBase;
+    DiffResource fComparison;
+    DiffResource fDifference;
+    DiffResource fWhite;
+
+    /// Arbitrary floating-point metric to be used to sort images from most
+    /// to least different from baseline; values of 0 will be omitted from the
+    /// summary webpage.
+    float fFractionDifference;
+    float fWeightedFraction;
+
+    float fAverageMismatchA;
+    float fAverageMismatchR;
+    float fAverageMismatchG;
+    float fAverageMismatchB;
+
+    uint32_t fTotalMismatchA;
+
+    uint32_t fMaxMismatchA;
+    uint32_t fMaxMismatchR;
+    uint32_t fMaxMismatchG;
+    uint32_t fMaxMismatchB;
+
+    /// Which category of diff result.
+    Result fResult;
+};
+
+typedef SkTDArray<DiffRecord*> RecordArray;
+
+/// A wrapper for any sortProc (comparison routine) which applies a first-order
+/// sort beforehand, and a tiebreaker if the sortProc returns 0.
+template<typename T> static int compare(const void* untyped_lhs, const void* untyped_rhs) {
+    const DiffRecord* lhs = *reinterpret_cast<DiffRecord* const *>(untyped_lhs);
+    const DiffRecord* rhs = *reinterpret_cast<DiffRecord* const *>(untyped_rhs);
+
+    // First-order sort... these comparisons should be applied before comparing
+    // pixel values, no matter what.
+    if (lhs->fResult != rhs->fResult) {
+        return (lhs->fResult < rhs->fResult) ? 1 : -1;
+    }
+
+    // Passed first-order sort, so call the pixel comparison routine.
+    int result = T::comparePixels(lhs, rhs);
+    if (result != 0) {
+        return result;
+    }
+
+    // Tiebreaker... if we got to this point, we don't really care
+    // which order they are sorted in, but let's at least be consistent.
+    return strcmp(lhs->fBase.fFilename.c_str(), rhs->fBase.fFilename.c_str());
+}
+
+/// Comparison routine for qsort; sorts by fFractionDifference
+/// from largest to smallest.
+class CompareDiffMetrics {
+public:
+    static int comparePixels(const DiffRecord* lhs, const DiffRecord* rhs) {
+        if (lhs->fFractionDifference < rhs->fFractionDifference) {
+          return 1;
+        }
+        if (rhs->fFractionDifference < lhs->fFractionDifference) {
+          return -1;
+        }
+        return 0;
+    }
+};
+
+class CompareDiffWeighted {
+public:
+    static int comparePixels(const DiffRecord* lhs, const DiffRecord* rhs) {
+        if (lhs->fWeightedFraction < rhs->fWeightedFraction) {
+            return 1;
+        }
+        if (lhs->fWeightedFraction > rhs->fWeightedFraction) {
+            return -1;
+        }
+        return 0;
+    }
+};
+
+/// Comparison routine for qsort;  sorts by max(fAverageMismatch{RGB})
+/// from largest to smallest.
+class CompareDiffMeanMismatches {
+public:
+    static int comparePixels(const DiffRecord* lhs, const DiffRecord* rhs) {
+        float leftValue = MAX3(lhs->fAverageMismatchR,
+                               lhs->fAverageMismatchG,
+                               lhs->fAverageMismatchB);
+        float rightValue = MAX3(rhs->fAverageMismatchR,
+                                rhs->fAverageMismatchG,
+                                rhs->fAverageMismatchB);
+        if (leftValue < rightValue) {
+            return 1;
+        }
+        if (rightValue < leftValue) {
+            return -1;
+        }
+        return 0;
+    }
+};
+
+/// Comparison routine for qsort;  sorts by max(fMaxMismatch{RGB})
+/// from largest to smallest.
+class CompareDiffMaxMismatches {
+public:
+    static int comparePixels(const DiffRecord* lhs, const DiffRecord* rhs) {
+        uint32_t leftValue = MAX3(lhs->fMaxMismatchR,
+                                  lhs->fMaxMismatchG,
+                                  lhs->fMaxMismatchB);
+        uint32_t rightValue = MAX3(rhs->fMaxMismatchR,
+                                   rhs->fMaxMismatchG,
+                                   rhs->fMaxMismatchB);
+        if (leftValue < rightValue) {
+            return 1;
+        }
+        if (rightValue < leftValue) {
+            return -1;
+        }
+
+        return CompareDiffMeanMismatches::comparePixels(lhs, rhs);
+    }
+};
+
+
+/// Parameterized routine to compute the color of a pixel in a difference image.
+typedef SkPMColor (*DiffMetricProc)(SkPMColor, SkPMColor);
+
+// from gm
+static inline SkPMColor compute_diff_pmcolor(SkPMColor c0, SkPMColor c1) {
+    int dr = SkGetPackedR32(c0) - SkGetPackedR32(c1);
+    int dg = SkGetPackedG32(c0) - SkGetPackedG32(c1);
+    int db = SkGetPackedB32(c0) - SkGetPackedB32(c1);
+
+    return SkPackARGB32(0xFF, SkAbs32(dr), SkAbs32(dg), SkAbs32(db));
+}
+
+/** When finished, dr->fResult should have some value other than kUnknown_Result.
+ *  Expects dr->fWhite.fBitmap and dr->fDifference.fBitmap to have the same bounds as
+ *  dr->fBase.fBitmap and have a valid pixelref.
+ */
+void compute_diff(DiffRecord* dr, DiffMetricProc diffFunction, const int colorThreshold);
+
+#endif
diff --git a/tools/skdiff/skdiff_html.cpp b/tools/skdiff/skdiff_html.cpp
new file mode 100644
index 0000000000..6f3c3b09e1
--- /dev/null
+++ b/tools/skdiff/skdiff_html.cpp
@@ -0,0 +1,313 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "skdiff.h"
+#include "skdiff_html.h"
+#include "SkStream.h"
+#include "SkTime.h"
+
+/// Make layout more consistent by scaling image to 240 height, 360 width,
+/// or natural size, whichever is smallest.
+static int compute_image_height(int height, int width) {
+    int retval = 240;
+    if (height < retval) {
+        retval = height;
+    }
+    float scale = (float) retval / height;
+    if (width * scale > 360) {
+        scale = (float) 360 / width;
+        retval = static_cast<int>(height * scale);
+    }
+    return retval;
+}
+
+static void print_table_header(SkFILEWStream* stream,
+                               const int matchCount,
+                               const int colorThreshold,
+                               const RecordArray& differences,
+                               const SkString &baseDir,
+                               const SkString &comparisonDir,
+                               bool doOutputDate = false) {
+    stream->writeText("<table>\n");
+    stream->writeText("<tr><th>");
+    stream->writeText("select image</th>\n<th>");
+    if (doOutputDate) {
+        SkTime::DateTime dt;
+        SkTime::GetDateTime(&dt);
+        stream->writeText("SkDiff run at ");
+        stream->writeDecAsText(dt.fHour);
+        stream->writeText(":");
+        if (dt.fMinute < 10) {
+            stream->writeText("0");
+        }
+        stream->writeDecAsText(dt.fMinute);
+        stream->writeText(":");
+        if (dt.fSecond < 10) {
+            stream->writeText("0");
+        }
+        stream->writeDecAsText(dt.fSecond);
+        stream->writeText("<br>");
+    }
+    stream->writeDecAsText(matchCount);
+    stream->writeText(" of ");
+    stream->writeDecAsText(differences.count());
+    stream->writeText(" diffs matched ");
+    if (colorThreshold == 0) {
+        stream->writeText("exactly");
+    } else {
+        stream->writeText("within ");
+        stream->writeDecAsText(colorThreshold);
+        stream->writeText(" color units per component");
+    }
+    stream->writeText(".<br>");
+    stream->writeText("</th>\n<th>");
+    stream->writeText("every different pixel shown in white");
+    stream->writeText("</th>\n<th>");
+    stream->writeText("color difference at each pixel");
+    stream->writeText("</th>\n<th>baseDir: ");
+    stream->writeText(baseDir.c_str());
+    stream->writeText("</th>\n<th>comparisonDir: ");
+    stream->writeText(comparisonDir.c_str());
+    stream->writeText("</th>\n");
+    stream->writeText("</tr>\n");
+}
+
+static void print_pixel_count(SkFILEWStream* stream, const DiffRecord& diff) {
+    stream->writeText("<br>(");
+    stream->writeDecAsText(static_cast<int>(diff.fFractionDifference *
+                                            diff.fBase.fBitmap.width() *
+                                            diff.fBase.fBitmap.height()));
+    stream->writeText(" pixels)");
+/*
+    stream->writeDecAsText(diff.fWeightedFraction *
+                           diff.fBaseWidth *
+                           diff.fBaseHeight);
+    stream->writeText(" weighted pixels)");
+*/
+}
+
+static void print_checkbox_cell(SkFILEWStream* stream, const DiffRecord& diff) {
+    stream->writeText("<td><input type=\"checkbox\" name=\"");
+    stream->writeText(diff.fBase.fFilename.c_str());
+    stream->writeText("\" checked=\"yes\"></td>");
+}
+
+static void print_label_cell(SkFILEWStream* stream, const DiffRecord& diff) {
+    char metricBuf [20];
+
+    stream->writeText("<td><b>");
+    stream->writeText(diff.fBase.fFilename.c_str());
+    stream->writeText("</b><br>");
+    switch (diff.fResult) {
+      case DiffRecord::kEqualBits_Result:
+        SkDEBUGFAIL("should not encounter DiffRecord with kEqualBits here");
+        return;
+      case DiffRecord::kEqualPixels_Result:
+        SkDEBUGFAIL("should not encounter DiffRecord with kEqualPixels here");
+        return;
+      case DiffRecord::kDifferentSizes_Result:
+        stream->writeText("Image sizes differ</td>");
+        return;
+      case DiffRecord::kDifferentPixels_Result:
+        sprintf(metricBuf, "%.4f%%", 100 * diff.fFractionDifference);
+        stream->writeText(metricBuf);
+        stream->writeText(" of pixels differ");
+        stream->writeText("\n  (");
+        sprintf(metricBuf, "%.4f%%", 100 * diff.fWeightedFraction);
+        stream->writeText(metricBuf);
+        stream->writeText(" weighted)");
+        // Write the actual number of pixels that differ if it's < 1%
+        if (diff.fFractionDifference < 0.01) {
+            print_pixel_count(stream, diff);
+        }
+        stream->writeText("<br>");
+        if (SkScalarRoundToInt(diff.fAverageMismatchA) > 0) {
+          stream->writeText("<br>Average alpha channel mismatch ");
+          stream->writeDecAsText(SkScalarRoundToInt(diff.fAverageMismatchA));
+        }
+
+        stream->writeText("<br>Max alpha channel mismatch ");
+        stream->writeDecAsText(SkScalarRoundToInt(diff.fMaxMismatchA));
+
+        stream->writeText("<br>Total alpha channel mismatch ");
+        stream->writeDecAsText(static_cast<int>(diff.fTotalMismatchA));
+
+        stream->writeText("<br>");
+        stream->writeText("<br>Average color mismatch ");
+        stream->writeDecAsText(SkScalarRoundToInt(MAX3(diff.fAverageMismatchR,
+                                                       diff.fAverageMismatchG,
+                                                       diff.fAverageMismatchB)));
+        stream->writeText("<br>Max color mismatch ");
+        stream->writeDecAsText(MAX3(diff.fMaxMismatchR,
+                                    diff.fMaxMismatchG,
+                                    diff.fMaxMismatchB));
+        stream->writeText("</td>");
+        break;
+      case DiffRecord::kCouldNotCompare_Result:
+        stream->writeText("Could not compare.<br>base: ");
+        stream->writeText(DiffResource::getStatusDescription(diff.fBase.fStatus));
+        stream->writeText("<br>comparison: ");
+        stream->writeText(DiffResource::getStatusDescription(diff.fComparison.fStatus));
+        stream->writeText("</td>");
+        return;
+      default:
+        SkDEBUGFAIL("encountered DiffRecord with unknown result type");
+        return;
+    }
+}
+
+static void print_image_cell(SkFILEWStream* stream, const SkString& path, int height) {
+    stream->writeText("<td><a href=\"");
+    stream->writeText(path.c_str());
+    stream->writeText("\"><img src=\"");
+    stream->writeText(path.c_str());
+    stream->writeText("\" height=\"");
+    stream->writeDecAsText(height);
+    stream->writeText("px\"></a></td>");
+}
+
+static void print_link_cell(SkFILEWStream* stream, const SkString& path, const char* text) {
+    stream->writeText("<td><a href=\"");
+    stream->writeText(path.c_str());
+    stream->writeText("\">");
+    stream->writeText(text);
+    stream->writeText("</a></td>");
+}
+
+static void print_diff_resource_cell(SkFILEWStream* stream, DiffResource& resource,
+                                     const SkString& relativePath, bool local) {
+    if (resource.fBitmap.empty()) {
+        if (DiffResource::kCouldNotDecode_Status == resource.fStatus) {
+            if (local && !resource.fFilename.isEmpty()) {
+                print_link_cell(stream, resource.fFilename, "N/A");
+                return;
+            }
+            if (!resource.fFullPath.isEmpty()) {
+                if (!resource.fFullPath.startsWith(PATH_DIV_STR)) {
+                    resource.fFullPath.prepend(relativePath);
+                }
+                print_link_cell(stream, resource.fFullPath, "N/A");
+                return;
+            }
+        }
+        stream->writeText("<td>N/A</td>");
+        return;
+    }
+
+    int height = compute_image_height(resource.fBitmap.height(), resource.fBitmap.width());
+    if (local) {
+        print_image_cell(stream, resource.fFilename, height);
+        return;
+    }
+    if (!resource.fFullPath.startsWith(PATH_DIV_STR)) {
+        resource.fFullPath.prepend(relativePath);
+    }
+    print_image_cell(stream, resource.fFullPath, height);
+}
+
+static void print_diff_row(SkFILEWStream* stream, DiffRecord& diff, const SkString& relativePath) {
+    stream->writeText("<tr>\n");
+    print_checkbox_cell(stream, diff);
+    print_label_cell(stream, diff);
+    print_diff_resource_cell(stream, diff.fWhite, relativePath, true);
+    print_diff_resource_cell(stream, diff.fDifference, relativePath, true);
+    print_diff_resource_cell(stream, diff.fBase, relativePath, false);
+    print_diff_resource_cell(stream, diff.fComparison, relativePath, false);
+    stream->writeText("</tr>\n");
+    stream->flush();
+}
+
+void print_diff_page(const int matchCount,
+                     const int colorThreshold,
+                     const RecordArray& differences,
+                     const SkString& baseDir,
+                     const SkString& comparisonDir,
+                     const SkString& outputDir) {
+
+    SkASSERT(!baseDir.isEmpty());
+    SkASSERT(!comparisonDir.isEmpty());
+    SkASSERT(!outputDir.isEmpty());
+
+    SkString outputPath(outputDir);
+    outputPath.append("index.html");
+    //SkFILEWStream outputStream ("index.html");
+    SkFILEWStream outputStream(outputPath.c_str());
+
+    // Need to convert paths from relative-to-cwd to relative-to-outputDir
+    // FIXME this doesn't work if there are '..' inside the outputDir
+
+    bool isPathAbsolute = false;
+    // On Windows or Linux, a path starting with PATH_DIV_CHAR is absolute.
+    if (outputDir.size() > 0 && PATH_DIV_CHAR == outputDir[0]) {
+        isPathAbsolute = true;
+    }
+#ifdef SK_BUILD_FOR_WIN32
+    // On Windows, absolute paths can also start with "x:", where x is any
+    // drive letter.
+    if (outputDir.size() > 1 && ':' == outputDir[1]) {
+        isPathAbsolute = true;
+    }
+#endif
+
+    SkString relativePath;
+    if (!isPathAbsolute) {
+        unsigned int ui;
+        for (ui = 0; ui < outputDir.size(); ui++) {
+            if (outputDir[ui] == PATH_DIV_CHAR) {
+                relativePath.append(".." PATH_DIV_STR);
+            }
+        }
+    }
+
+    outputStream.writeText(
+        "<html>\n<head>\n"
+        "<script src=\"https://ajax.googleapis.com/ajax/"
+        "libs/jquery/1.7.2/jquery.min.js\"></script>\n"
+        "<script type=\"text/javascript\">\n"
+        "function generateCheckedList() {\n"
+        "var boxes = $(\":checkbox:checked\");\n"
+        "var fileCmdLineString = '';\n"
+        "var fileMultiLineString = '';\n"
+        "for (var i = 0; i < boxes.length; i++) {\n"
+        "fileMultiLineString += boxes[i].name + '<br>';\n"
+        "fileCmdLineString += boxes[i].name + '&nbsp;';\n"
+        "}\n"
+        "$(\"#checkedList\").html(fileCmdLineString + "
+        "'<br><br>' + fileMultiLineString);\n"
+        "}\n"
+        "</script>\n</head>\n<body>\n");
+    print_table_header(&outputStream, matchCount, colorThreshold, differences,
+                       baseDir, comparisonDir);
+    int i;
+    for (i = 0; i < differences.count(); i++) {
+        DiffRecord* diff = differences[i];
+
+        switch (diff->fResult) {
+          // Cases in which there is no diff to report.
+          case DiffRecord::kEqualBits_Result:
+          case DiffRecord::kEqualPixels_Result:
+            continue;
+          // Cases in which we want a detailed pixel diff.
+          case DiffRecord::kDifferentPixels_Result:
+          case DiffRecord::kDifferentSizes_Result:
+          case DiffRecord::kCouldNotCompare_Result:
+            print_diff_row(&outputStream, *diff, relativePath);
+            continue;
+          default:
+            SkDEBUGFAIL("encountered DiffRecord with unknown result type");
+            continue;
+        }
+    }
+    outputStream.writeText(
+        "</table>\n"
+        "<input type=\"button\" "
+        "onclick=\"generateCheckedList()\" "
+        "value=\"Create Rebaseline List\">\n"
+        "<div id=\"checkedList\"></div>\n"
+        "</body>\n</html>\n");
+    outputStream.flush();
+}
diff --git a/tools/skdiff/skdiff_html.h b/tools/skdiff/skdiff_html.h
new file mode 100644
index 0000000000..eefbebf2fd
--- /dev/null
+++ b/tools/skdiff/skdiff_html.h
@@ -0,0 +1,21 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef skdiff_html_DEFINED
+#define skdiff_html_DEFINED
+
+#include "skdiff.h"
+class SkString;
+
+void print_diff_page(const int matchCount,
+                     const int colorThreshold,
+                     const RecordArray& differences,
+                     const SkString& baseDir,
+                     const SkString& comparisonDir,
+                     const SkString& outputDir);
+
+#endif
diff --git a/tools/skdiff/skdiff_image.cpp b/tools/skdiff/skdiff_image.cpp
new file mode 100644
index 0000000000..287523de15
--- /dev/null
+++ b/tools/skdiff/skdiff_image.cpp
@@ -0,0 +1,374 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "skdiff.h"
+#include "skdiff_utils.h"
+#include "SkBitmap.h"
+#include "SkData.h"
+#include "SkImageEncoder.h"
+#include "SkOSFile.h"
+#include "SkTypes.h"
+
+#include <stdio.h>
+
+/// If outputDir.isEmpty(), don't write out diff files.
+static void create_diff_images (DiffMetricProc dmp,
+                                const int colorThreshold,
+                                const SkString& baseFile,
+                                const SkString& comparisonFile,
+                                const SkString& outputDir,
+                                const SkString& outputFilename,
+                                DiffRecord* drp) {
+    SkASSERT(!baseFile.isEmpty());
+    SkASSERT(!comparisonFile.isEmpty());
+
+    drp->fBase.fFilename = baseFile;
+    drp->fBase.fFullPath = baseFile;
+    drp->fBase.fStatus = DiffResource::kSpecified_Status;
+
+    drp->fComparison.fFilename = comparisonFile;
+    drp->fComparison.fFullPath = comparisonFile;
+    drp->fComparison.fStatus = DiffResource::kSpecified_Status;
+
+    sk_sp<SkData> baseFileBits = read_file(drp->fBase.fFullPath.c_str());
+    if (baseFileBits) {
+        drp->fBase.fStatus = DiffResource::kRead_Status;
+    }
+    sk_sp<SkData> comparisonFileBits = read_file(drp->fComparison.fFullPath.c_str());
+    if (comparisonFileBits) {
+        drp->fComparison.fStatus = DiffResource::kRead_Status;
+    }
+    if (nullptr == baseFileBits || nullptr == comparisonFileBits) {
+        if (nullptr == baseFileBits) {
+            drp->fBase.fStatus = DiffResource::kCouldNotRead_Status;
+        }
+        if (nullptr == comparisonFileBits) {
+            drp->fComparison.fStatus = DiffResource::kCouldNotRead_Status;
+        }
+        drp->fResult = DiffRecord::kCouldNotCompare_Result;
+        return;
+    }
+
+    if (are_buffers_equal(baseFileBits.get(), comparisonFileBits.get())) {
+        drp->fResult = DiffRecord::kEqualBits_Result;
+        return;
+    }
+
+    get_bitmap(baseFileBits, drp->fBase, false);
+    get_bitmap(comparisonFileBits, drp->fComparison, false);
+    if (DiffResource::kDecoded_Status != drp->fBase.fStatus ||
+        DiffResource::kDecoded_Status != drp->fComparison.fStatus)
+    {
+        drp->fResult = DiffRecord::kCouldNotCompare_Result;
+        return;
+    }
+
+    create_and_write_diff_image(drp, dmp, colorThreshold, outputDir, outputFilename);
+    //TODO: copy fBase.fFilename and fComparison.fFilename to outputDir
+    //      svn and git often present tmp files to diff tools which are promptly deleted
+
+    //TODO: serialize drp to outputDir
+    //      write a tool to deserialize them and call print_diff_page
+
+    SkASSERT(DiffRecord::kUnknown_Result != drp->fResult);
+}
+
+static void usage (char * argv0) {
+    SkDebugf("Skia image diff tool\n");
+    SkDebugf("\n"
+"Usage: \n"
+"    %s <baseFile> <comparisonFile>\n" , argv0);
+    SkDebugf(
+"\nArguments:"
+"\n    --failonresult <result>: After comparing all file pairs, exit with nonzero"
+"\n                             return code (number of file pairs yielding this"
+"\n                             result) if any file pairs yielded this result."
+"\n                             This flag may be repeated, in which case the"
+"\n                             return code will be the number of fail pairs"
+"\n                             yielding ANY of these results."
+"\n    --failonstatus <baseStatus> <comparisonStatus>: exit with nonzero return"
+"\n                             code if any file pairs yeilded this status."
+"\n    --help: display this info"
+"\n    --listfilenames: list all filenames for each result type in stdout"
+"\n    --nodiffs: don't write out image diffs, just generate report on stdout"
+"\n    --outputdir: directory to write difference images"
+"\n    --threshold <n>: only report differences > n (per color channel) [default 0]"
+"\n    -u: ignored. Recognized for compatibility with svn diff."
+"\n    -L: first occurrence label for base, second occurrence label for comparison."
+"\n        Labels must be of the form \"<filename>(\t<specifier>)?\"."
+"\n        The base <filename> will be used to create files in outputdir."
+"\n"
+"\n    baseFile: baseline image file."
+"\n    comparisonFile: comparison image file"
+"\n"
+"\nIf no sort is specified, it will sort by fraction of pixels mismatching."
+"\n");
+}
+
+const int kNoError = 0;
+const int kGenericError = -1;
+
+int tool_main(int argc, char** argv);
+int tool_main(int argc, char** argv) {
+    DiffMetricProc diffProc = compute_diff_pmcolor;
+
+    // Maximum error tolerated in any one color channel in any one pixel before
+    // a difference is reported.
+    int colorThreshold = 0;
+    SkString baseFile;
+    SkString baseLabel;
+    SkString comparisonFile;
+    SkString comparisonLabel;
+    SkString outputDir;
+
+    bool listFilenames = false;
+
+    bool failOnResultType[DiffRecord::kResultCount];
+    for (int i = 0; i < DiffRecord::kResultCount; i++) {
+        failOnResultType[i] = false;
+    }
+
+    bool failOnStatusType[DiffResource::kStatusCount][DiffResource::kStatusCount];
+    for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+        for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+            failOnStatusType[base][comparison] = false;
+        }
+    }
+
+    int i;
+    int numUnflaggedArguments = 0;
+    int numLabelArguments = 0;
+    for (i = 1; i < argc; i++) {
+        if (!strcmp(argv[i], "--failonresult")) {
+            if (argc == ++i) {
+                SkDebugf("failonresult expects one argument.\n");
+                continue;
+            }
+            DiffRecord::Result type = DiffRecord::getResultByName(argv[i]);
+            if (type != DiffRecord::kResultCount) {
+                failOnResultType[type] = true;
+            } else {
+                SkDebugf("ignoring unrecognized result <%s>\n", argv[i]);
+            }
+            continue;
+        }
+        if (!strcmp(argv[i], "--failonstatus")) {
+            if (argc == ++i) {
+                SkDebugf("failonstatus missing base status.\n");
+                continue;
+            }
+            bool baseStatuses[DiffResource::kStatusCount];
+            if (!DiffResource::getMatchingStatuses(argv[i], baseStatuses)) {
+                SkDebugf("unrecognized base status <%s>\n", argv[i]);
+            }
+
+            if (argc == ++i) {
+                SkDebugf("failonstatus missing comparison status.\n");
+                continue;
+            }
+            bool comparisonStatuses[DiffResource::kStatusCount];
+            if (!DiffResource::getMatchingStatuses(argv[i], comparisonStatuses)) {
+                SkDebugf("unrecognized comarison status <%s>\n", argv[i]);
+            }
+
+            for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+                for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+                    failOnStatusType[base][comparison] |=
+                        baseStatuses[base] && comparisonStatuses[comparison];
+                }
+            }
+            continue;
+        }
+        if (!strcmp(argv[i], "--help")) {
+            usage(argv[0]);
+            return kNoError;
+        }
+        if (!strcmp(argv[i], "--listfilenames")) {
+            listFilenames = true;
+            continue;
+        }
+        if (!strcmp(argv[i], "--outputdir")) {
+            if (argc == ++i) {
+                SkDebugf("outputdir expects one argument.\n");
+                continue;
+            }
+            outputDir.set(argv[i]);
+            continue;
+        }
+        if (!strcmp(argv[i], "--threshold")) {
+            colorThreshold = atoi(argv[++i]);
+            continue;
+        }
+        if (!strcmp(argv[i], "-u")) {
+            //we don't produce unified diffs, ignore parameter to work with svn diff
+            continue;
+        }
+        if (!strcmp(argv[i], "-L")) {
+            if (argc == ++i) {
+                SkDebugf("label expects one argument.\n");
+                continue;
+            }
+            switch (numLabelArguments++) {
+                case 0:
+                    baseLabel.set(argv[i]);
+                    continue;
+                case 1:
+                    comparisonLabel.set(argv[i]);
+                    continue;
+                default:
+                    SkDebugf("extra label argument <%s>\n", argv[i]);
+                    usage(argv[0]);
+                    return kGenericError;
+            }
+            continue;
+        }
+        if (argv[i][0] != '-') {
+            switch (numUnflaggedArguments++) {
+                case 0:
+                    baseFile.set(argv[i]);
+                    continue;
+                case 1:
+                    comparisonFile.set(argv[i]);
+                    continue;
+                default:
+                    SkDebugf("extra unflagged argument <%s>\n", argv[i]);
+                    usage(argv[0]);
+                    return kGenericError;
+            }
+        }
+
+        SkDebugf("Unrecognized argument <%s>\n", argv[i]);
+        usage(argv[0]);
+        return kGenericError;
+    }
+
+    if (numUnflaggedArguments != 2) {
+        usage(argv[0]);
+        return kGenericError;
+    }
+
+    if (listFilenames) {
+        printf("Base file is [%s]\n", baseFile.c_str());
+    }
+
+    if (listFilenames) {
+        printf("Comparison file is [%s]\n", comparisonFile.c_str());
+    }
+
+    if (outputDir.isEmpty()) {
+        if (listFilenames) {
+            printf("Not writing any diffs. No output dir specified.\n");
+        }
+    } else {
+        if (!outputDir.endsWith(PATH_DIV_STR)) {
+            outputDir.append(PATH_DIV_STR);
+        }
+        if (listFilenames) {
+            printf("Writing diffs. Output dir is [%s]\n", outputDir.c_str());
+        }
+    }
+
+    // Some obscure documentation about diff/patch labels:
+    //
+    // Posix says the format is: <filename><tab><date>
+    //     It also states that if a filename contains <tab> or <newline>
+    //     the result is implementation defined
+    //
+    // Svn diff --diff-cmd provides labels of the form: <filename><tab><revision>
+    //
+    // Git diff --ext-diff does not supply arguments compatible with diff.
+    //     However, it does provide the filename directly.
+    //     skimagediff_git.sh: skimagediff %2 %5 -L "%1\t(%3)" -L "%1\t(%6)"
+    //
+    // Git difftool sets $LOCAL, $REMOTE, $MERGED, and $BASE instead of command line parameters.
+    //     difftool.<>.cmd: skimagediff $LOCAL $REMOTE -L "$MERGED\t(local)" -L "$MERGED\t(remote)"
+    //
+    // Diff will write any specified label verbatim. Without a specified label diff will write
+    //     <filename><tab><date>
+    //     However, diff will encode the filename as a cstring if the filename contains
+    //         Any of <space> or <double quote>
+    //         A char less than 32
+    //         Any escapable character \\, \a, \b, \t, \n, \v, \f, \r
+    //
+    // Patch decodes:
+    //     If first <non-white-space> is <double quote>, parse filename from cstring.
+    //     If there is a <tab> after the first <non-white-space>, filename is
+    //         [first <non-white-space>, the next run of <white-space> with an embedded <tab>).
+    //     Otherwise the filename is [first <non-space>, the next <white-space>).
+    //
+    // The filename /dev/null means the file does not exist (used in adds and deletes).
+
+    // Considering the above, skimagediff will consider the contents of a -L parameter as
+    //     <filename>(\t<specifier>)?
+    SkString outputFile;
+
+    if (baseLabel.isEmpty()) {
+        baseLabel.set(baseFile);
+        outputFile = baseLabel;
+    } else {
+        const char* baseLabelCstr = baseLabel.c_str();
+        const char* tab = strchr(baseLabelCstr, '\t');
+        if (nullptr == tab) {
+            outputFile = baseLabel;
+        } else {
+            outputFile.set(baseLabelCstr, tab - baseLabelCstr);
+        }
+    }
+    if (comparisonLabel.isEmpty()) {
+        comparisonLabel.set(comparisonFile);
+    }
+    printf("Base:       %s\n", baseLabel.c_str());
+    printf("Comparison: %s\n", comparisonLabel.c_str());
+
+    DiffRecord dr;
+    create_diff_images(diffProc, colorThreshold, baseFile, comparisonFile, outputDir, outputFile,
+                       &dr);
+
+    if (DiffResource::isStatusFailed(dr.fBase.fStatus)) {
+        printf("Base %s.\n", DiffResource::getStatusDescription(dr.fBase.fStatus));
+    }
+    if (DiffResource::isStatusFailed(dr.fComparison.fStatus)) {
+        printf("Comparison %s.\n", DiffResource::getStatusDescription(dr.fComparison.fStatus));
+    }
+    printf("Base and Comparison %s.\n", DiffRecord::getResultDescription(dr.fResult));
+
+    if (DiffRecord::kDifferentPixels_Result == dr.fResult) {
+        printf("%.4f%% of pixels differ", 100 * dr.fFractionDifference);
+        printf(" (%.4f%%  weighted)", 100 * dr.fWeightedFraction);
+        if (dr.fFractionDifference < 0.01) {
+            printf(" %d pixels", static_cast<int>(dr.fFractionDifference *
+                                                  dr.fBase.fBitmap.width() *
+                                                  dr.fBase.fBitmap.height()));
+        }
+
+        printf("\nAverage color mismatch: ");
+        printf("%d", static_cast<int>(MAX3(dr.fAverageMismatchR,
+                                           dr.fAverageMismatchG,
+                                           dr.fAverageMismatchB)));
+        printf("\nMax color mismatch: ");
+        printf("%d", MAX3(dr.fMaxMismatchR,
+                          dr.fMaxMismatchG,
+                          dr.fMaxMismatchB));
+        printf("\n");
+    }
+    printf("\n");
+
+    int num_failing_results = 0;
+    if (failOnResultType[dr.fResult]) {
+        ++num_failing_results;
+    }
+    if (failOnStatusType[dr.fBase.fStatus][dr.fComparison.fStatus]) {
+        ++num_failing_results;
+    }
+
+    return num_failing_results;
+}
+
+#if !defined SK_BUILD_FOR_IOS
+int main(int argc, char * const argv[]) {
+    return tool_main(argc, (char**) argv);
+}
+#endif
diff --git a/tools/skdiff/skdiff_main.cpp b/tools/skdiff/skdiff_main.cpp
new file mode 100644
index 0000000000..c51cd28d78
--- /dev/null
+++ b/tools/skdiff/skdiff_main.cpp
@@ -0,0 +1,862 @@
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "skdiff.h"
+#include "skdiff_html.h"
+#include "skdiff_utils.h"
+#include "SkBitmap.h"
+#include "SkData.h"
+#include "SkForceLinking.h"
+#include "SkImageEncoder.h"
+#include "SkOSFile.h"
+#include "SkStream.h"
+#include "../private/SkTDArray.h"
+#include "../private/SkTSearch.h"
+
+#include <stdlib.h>
+
+__SK_FORCE_IMAGE_DECODER_LINKING;
+
+/**
+ * skdiff
+ *
+ * Given three directory names, expects to find identically-named files in
+ * each of the first two; the first are treated as a set of baseline,
+ * the second a set of variant images, and a diff image is written into the
+ * third directory for each pair.
+ * Creates an index.html in the current third directory to compare each
+ * pair that does not match exactly.
+ * Recursively descends directories, unless run with --norecurse.
+ *
+ * Returns zero exit code if all images match across baseDir and comparisonDir.
+ */
+
+typedef SkTDArray<SkString*> StringArray;
+typedef StringArray FileArray;
+
+static void add_unique_basename(StringArray* array, const SkString& filename) {
+    // trim off dirs
+    const char* src = filename.c_str();
+    const char* trimmed = strrchr(src, SkPATH_SEPARATOR);
+    if (trimmed) {
+        trimmed += 1;   // skip the separator
+    } else {
+        trimmed = src;
+    }
+    const char* end = strrchr(trimmed, '.');
+    if (!end) {
+        end = trimmed + strlen(trimmed);
+    }
+    SkString result(trimmed, end - trimmed);
+
+    // only add unique entries
+    for (int i = 0; i < array->count(); ++i) {
+        if (*array->getAt(i) == result) {
+            return;
+        }
+    }
+    *array->append() = new SkString(result);
+}
+
+struct DiffSummary {
+    DiffSummary ()
+        : fNumMatches(0)
+        , fNumMismatches(0)
+        , fMaxMismatchV(0)
+        , fMaxMismatchPercent(0) { }
+
+    ~DiffSummary() {
+        for (int i = 0; i < DiffRecord::kResultCount; ++i) {
+            fResultsOfType[i].deleteAll();
+        }
+        for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+            for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+                fStatusOfType[base][comparison].deleteAll();
+            }
+        }
+    }
+
+    uint32_t fNumMatches;
+    uint32_t fNumMismatches;
+    uint32_t fMaxMismatchV;
+    float fMaxMismatchPercent;
+
+    FileArray fResultsOfType[DiffRecord::kResultCount];
+    FileArray fStatusOfType[DiffResource::kStatusCount][DiffResource::kStatusCount];
+
+    StringArray fFailedBaseNames[DiffRecord::kResultCount];
+
+    void printContents(const FileArray& fileArray,
+                       const char* baseStatus, const char* comparisonStatus,
+                       bool listFilenames) {
+        int n = fileArray.count();
+        printf("%d file pairs %s in baseDir and %s in comparisonDir",
+                n,            baseStatus,       comparisonStatus);
+        if (listFilenames) {
+            printf(": ");
+            for (int i = 0; i < n; ++i) {
+                printf("%s ", fileArray[i]->c_str());
+            }
+        }
+        printf("\n");
+    }
+
+    void printStatus(bool listFilenames,
+                     bool failOnStatusType[DiffResource::kStatusCount]
+                                          [DiffResource::kStatusCount]) {
+        typedef DiffResource::Status Status;
+
+        for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+            Status baseStatus = static_cast<Status>(base);
+            for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+                Status comparisonStatus = static_cast<Status>(comparison);
+                const FileArray& fileArray = fStatusOfType[base][comparison];
+                if (fileArray.count() > 0) {
+                    if (failOnStatusType[base][comparison]) {
+                        printf("   [*] ");
+                    } else {
+                        printf("   [_] ");
+                    }
+                    printContents(fileArray,
+                                  DiffResource::getStatusDescription(baseStatus),
+                                  DiffResource::getStatusDescription(comparisonStatus),
+                                  listFilenames);
+                }
+            }
+        }
+    }
+
+    // Print a line about the contents of this FileArray to stdout.
+    void printContents(const FileArray& fileArray, const char* headerText, bool listFilenames) {
+        int n = fileArray.count();
+        printf("%d file pairs %s", n, headerText);
+        if (listFilenames) {
+            printf(": ");
+            for (int i = 0; i < n; ++i) {
+                printf("%s ", fileArray[i]->c_str());
+            }
+        }
+        printf("\n");
+    }
+
+    void print(bool listFilenames, bool failOnResultType[DiffRecord::kResultCount],
+               bool failOnStatusType[DiffResource::kStatusCount]
+                                    [DiffResource::kStatusCount]) {
+        printf("\ncompared %d file pairs:\n", fNumMatches + fNumMismatches);
+        for (int resultInt = 0; resultInt < DiffRecord::kResultCount; ++resultInt) {
+            DiffRecord::Result result = static_cast<DiffRecord::Result>(resultInt);
+            if (failOnResultType[result]) {
+                printf("[*] ");
+            } else {
+                printf("[_] ");
+            }
+            printContents(fResultsOfType[result], DiffRecord::getResultDescription(result),
+                          listFilenames);
+            if (DiffRecord::kCouldNotCompare_Result == result) {
+                printStatus(listFilenames, failOnStatusType);
+            }
+        }
+        printf("(results marked with [*] will cause nonzero return value)\n");
+        printf("\nnumber of mismatching file pairs: %d\n", fNumMismatches);
+        if (fNumMismatches > 0) {
+            printf("Maximum pixel intensity mismatch %d\n", fMaxMismatchV);
+            printf("Largest area mismatch was %.2f%% of pixels\n",fMaxMismatchPercent);
+        }
+    }
+
+    void printfFailingBaseNames(const char separator[]) {
+        for (int resultInt = 0; resultInt < DiffRecord::kResultCount; ++resultInt) {
+            const StringArray& array = fFailedBaseNames[resultInt];
+            if (array.count()) {
+                printf("%s [%d]%s", DiffRecord::ResultNames[resultInt], array.count(), separator);
+                for (int j = 0; j < array.count(); ++j) {
+                    printf("%s%s", array[j]->c_str(), separator);
+                }
+                printf("\n");
+            }
+        }
+    }
+
+    void add (DiffRecord* drp) {
+        uint32_t mismatchValue;
+
+        if (drp->fBase.fFilename.equals(drp->fComparison.fFilename)) {
+            fResultsOfType[drp->fResult].push(new SkString(drp->fBase.fFilename));
+        } else {
+            SkString* blame = new SkString("(");
+            blame->append(drp->fBase.fFilename);
+            blame->append(", ");
+            blame->append(drp->fComparison.fFilename);
+            blame->append(")");
+            fResultsOfType[drp->fResult].push(blame);
+        }
+        switch (drp->fResult) {
+          case DiffRecord::kEqualBits_Result:
+            fNumMatches++;
+            break;
+          case DiffRecord::kEqualPixels_Result:
+            fNumMatches++;
+            break;
+          case DiffRecord::kDifferentSizes_Result:
+            fNumMismatches++;
+            break;
+          case DiffRecord::kDifferentPixels_Result:
+            fNumMismatches++;
+            if (drp->fFractionDifference * 100 > fMaxMismatchPercent) {
+                fMaxMismatchPercent = drp->fFractionDifference * 100;
+            }
+            mismatchValue = MAX3(drp->fMaxMismatchR, drp->fMaxMismatchG,
+                                 drp->fMaxMismatchB);
+            if (mismatchValue > fMaxMismatchV) {
+                fMaxMismatchV = mismatchValue;
+            }
+            break;
+          case DiffRecord::kCouldNotCompare_Result:
+            fNumMismatches++;
+            fStatusOfType[drp->fBase.fStatus][drp->fComparison.fStatus].push(
+                    new SkString(drp->fBase.fFilename));
+            break;
+          case DiffRecord::kUnknown_Result:
+            SkDEBUGFAIL("adding uncategorized DiffRecord");
+            break;
+          default:
+            SkDEBUGFAIL("adding DiffRecord with unhandled fResult value");
+            break;
+        }
+
+        switch (drp->fResult) {
+            case DiffRecord::kEqualBits_Result:
+            case DiffRecord::kEqualPixels_Result:
+                break;
+            default:
+                add_unique_basename(&fFailedBaseNames[drp->fResult], drp->fBase.fFilename);
+                break;
+        }
+    }
+};
+
+/// Returns true if string contains any of these substrings.
+static bool string_contains_any_of(const SkString& string,
+                                   const StringArray& substrings) {
+    for (int i = 0; i < substrings.count(); i++) {
+        if (string.contains(substrings[i]->c_str())) {
+            return true;
+        }
+    }
+    return false;
+}
+
+/// Internal (potentially recursive) implementation of get_file_list.
+static void get_file_list_subdir(const SkString& rootDir, const SkString& subDir,
+                                 const StringArray& matchSubstrings,
+                                 const StringArray& nomatchSubstrings,
+                                 bool recurseIntoSubdirs, FileArray *files) {
+    bool isSubDirEmpty = subDir.isEmpty();
+    SkString dir(rootDir);
+    if (!isSubDirEmpty) {
+        dir.append(PATH_DIV_STR);
+        dir.append(subDir);
+    }
+
+    // Iterate over files (not directories) within dir.
+    SkOSFile::Iter fileIterator(dir.c_str());
+    SkString fileName;
+    while (fileIterator.next(&fileName, false)) {
+        if (fileName.startsWith(".")) {
+            continue;
+        }
+        SkString pathRelativeToRootDir(subDir);
+        if (!isSubDirEmpty) {
+            pathRelativeToRootDir.append(PATH_DIV_STR);
+        }
+        pathRelativeToRootDir.append(fileName);
+        if (string_contains_any_of(pathRelativeToRootDir, matchSubstrings) &&
+            !string_contains_any_of(pathRelativeToRootDir, nomatchSubstrings)) {
+            files->push(new SkString(pathRelativeToRootDir));
+        }
+    }
+
+    // Recurse into any non-ignored subdirectories.
+    if (recurseIntoSubdirs) {
+        SkOSFile::Iter dirIterator(dir.c_str());
+        SkString dirName;
+        while (dirIterator.next(&dirName, true)) {
+            if (dirName.startsWith(".")) {
+                continue;
+            }
+            SkString pathRelativeToRootDir(subDir);
+            if (!isSubDirEmpty) {
+                pathRelativeToRootDir.append(PATH_DIV_STR);
+            }
+            pathRelativeToRootDir.append(dirName);
+            if (!string_contains_any_of(pathRelativeToRootDir, nomatchSubstrings)) {
+                get_file_list_subdir(rootDir, pathRelativeToRootDir,
+                                     matchSubstrings, nomatchSubstrings, recurseIntoSubdirs,
+                                     files);
+            }
+        }
+    }
+}
+
+/// Iterate over dir and get all files whose filename:
+///  - matches any of the substrings in matchSubstrings, but...
+///  - DOES NOT match any of the substrings in nomatchSubstrings
+///  - DOES NOT start with a dot (.)
+/// Adds the matching files to the list in *files.
+static void get_file_list(const SkString& dir,
+                          const StringArray& matchSubstrings,
+                          const StringArray& nomatchSubstrings,
+                          bool recurseIntoSubdirs, FileArray *files) {
+    get_file_list_subdir(dir, SkString(""),
+                         matchSubstrings, nomatchSubstrings, recurseIntoSubdirs,
+                         files);
+}
+
+static void release_file_list(FileArray *files) {
+    files->deleteAll();
+}
+
+/// Comparison routines for qsort, sort by file names.
+static int compare_file_name_metrics(SkString **lhs, SkString **rhs) {
+    return strcmp((*lhs)->c_str(), (*rhs)->c_str());
+}
+
+class AutoReleasePixels {
+public:
+    AutoReleasePixels(DiffRecord* drp)
+    : fDrp(drp) {
+        SkASSERT(drp != nullptr);
+    }
+    ~AutoReleasePixels() {
+        fDrp->fBase.fBitmap.setPixelRef(nullptr);
+        fDrp->fComparison.fBitmap.setPixelRef(nullptr);
+        fDrp->fDifference.fBitmap.setPixelRef(nullptr);
+        fDrp->fWhite.fBitmap.setPixelRef(nullptr);
+    }
+
+private:
+    DiffRecord* fDrp;
+};
+
+static void get_bounds(DiffResource& resource, const char* name) {
+    if (resource.fBitmap.empty() && !DiffResource::isStatusFailed(resource.fStatus)) {
+        sk_sp<SkData> fileBits(read_file(resource.fFullPath.c_str()));
+        if (fileBits) {
+            get_bitmap(fileBits, resource, true);
+        } else {
+            SkDebugf("WARNING: couldn't read %s file <%s>\n", name, resource.fFullPath.c_str());
+            resource.fStatus = DiffResource::kCouldNotRead_Status;
+        }
+    }
+}
+
+static void get_bounds(DiffRecord& drp) {
+    get_bounds(drp.fBase, "base");
+    get_bounds(drp.fComparison, "comparison");
+}
+
+#ifdef SK_OS_WIN
+#define ANSI_COLOR_RED     ""
+#define ANSI_COLOR_GREEN   ""
+#define ANSI_COLOR_YELLOW  ""
+#define ANSI_COLOR_RESET   ""
+#else
+#define ANSI_COLOR_RED     "\x1b[31m"
+#define ANSI_COLOR_GREEN   "\x1b[32m"
+#define ANSI_COLOR_YELLOW  "\x1b[33m"
+#define ANSI_COLOR_RESET   "\x1b[0m"
+#endif
+
+#define VERBOSE_STATUS(status,color,filename) if (verbose) printf( "[ " color " %10s " ANSI_COLOR_RESET " ] %s\n", status, filename->c_str())
+
+/// Creates difference images, returns the number that have a 0 metric.
+/// If outputDir.isEmpty(), don't write out diff files.
+static void create_diff_images (DiffMetricProc dmp,
+                                const int colorThreshold,
+                                RecordArray* differences,
+                                const SkString& baseDir,
+                                const SkString& comparisonDir,
+                                const SkString& outputDir,
+                                const StringArray& matchSubstrings,
+                                const StringArray& nomatchSubstrings,
+                                bool recurseIntoSubdirs,
+                                bool getBounds,
+                                bool verbose,
+                                DiffSummary* summary) {
+    SkASSERT(!baseDir.isEmpty());
+    SkASSERT(!comparisonDir.isEmpty());
+
+    FileArray baseFiles;
+    FileArray comparisonFiles;
+
+    get_file_list(baseDir, matchSubstrings, nomatchSubstrings, recurseIntoSubdirs, &baseFiles);
+    get_file_list(comparisonDir, matchSubstrings, nomatchSubstrings, recurseIntoSubdirs,
+                  &comparisonFiles);
+
+    if (!baseFiles.isEmpty()) {
+        qsort(baseFiles.begin(), baseFiles.count(), sizeof(SkString*),
+              SkCastForQSort(compare_file_name_metrics));
+    }
+    if (!comparisonFiles.isEmpty()) {
+        qsort(comparisonFiles.begin(), comparisonFiles.count(),
+              sizeof(SkString*), SkCastForQSort(compare_file_name_metrics));
+    }
+
+    if (!outputDir.isEmpty()) {
+        sk_mkdir(outputDir.c_str());
+    }
+
+    int i = 0;
+    int j = 0;
+
+    while (i < baseFiles.count() &&
+           j < comparisonFiles.count()) {
+
+        SkString basePath(baseDir);
+        SkString comparisonPath(comparisonDir);
+
+        DiffRecord *drp = new DiffRecord;
+        int v = strcmp(baseFiles[i]->c_str(), comparisonFiles[j]->c_str());
+
+        if (v < 0) {
+            // in baseDir, but not in comparisonDir
+            drp->fResult = DiffRecord::kCouldNotCompare_Result;
+
+            basePath.append(*baseFiles[i]);
+            comparisonPath.append(*baseFiles[i]);
+
+            drp->fBase.fFilename = *baseFiles[i];
+            drp->fBase.fFullPath = basePath;
+            drp->fBase.fStatus = DiffResource::kExists_Status;
+
+            drp->fComparison.fFilename = *baseFiles[i];
+            drp->fComparison.fFullPath = comparisonPath;
+            drp->fComparison.fStatus = DiffResource::kDoesNotExist_Status;
+
+            VERBOSE_STATUS("MISSING", ANSI_COLOR_YELLOW, baseFiles[i]);
+
+            ++i;
+        } else if (v > 0) {
+            // in comparisonDir, but not in baseDir
+            drp->fResult = DiffRecord::kCouldNotCompare_Result;
+
+            basePath.append(*comparisonFiles[j]);
+            comparisonPath.append(*comparisonFiles[j]);
+
+            drp->fBase.fFilename = *comparisonFiles[j];
+            drp->fBase.fFullPath = basePath;
+            drp->fBase.fStatus = DiffResource::kDoesNotExist_Status;
+
+            drp->fComparison.fFilename = *comparisonFiles[j];
+            drp->fComparison.fFullPath = comparisonPath;
+            drp->fComparison.fStatus = DiffResource::kExists_Status;
+
+            VERBOSE_STATUS("MISSING", ANSI_COLOR_YELLOW, comparisonFiles[j]);
+
+            ++j;
+        } else {
+            // Found the same filename in both baseDir and comparisonDir.
+            SkASSERT(DiffRecord::kUnknown_Result == drp->fResult);
+
+            basePath.append(*baseFiles[i]);
+            comparisonPath.append(*comparisonFiles[j]);
+
+            drp->fBase.fFilename = *baseFiles[i];
+            drp->fBase.fFullPath = basePath;
+            drp->fBase.fStatus = DiffResource::kExists_Status;
+
+            drp->fComparison.fFilename = *comparisonFiles[j];
+            drp->fComparison.fFullPath = comparisonPath;
+            drp->fComparison.fStatus = DiffResource::kExists_Status;
+
+            sk_sp<SkData> baseFileBits(read_file(drp->fBase.fFullPath.c_str()));
+            if (baseFileBits) {
+                drp->fBase.fStatus = DiffResource::kRead_Status;
+            }
+            sk_sp<SkData> comparisonFileBits(read_file(drp->fComparison.fFullPath.c_str()));
+            if (comparisonFileBits) {
+                drp->fComparison.fStatus = DiffResource::kRead_Status;
+            }
+            if (nullptr == baseFileBits || nullptr == comparisonFileBits) {
+                if (nullptr == baseFileBits) {
+                    drp->fBase.fStatus = DiffResource::kCouldNotRead_Status;
+                    VERBOSE_STATUS("READ FAIL", ANSI_COLOR_RED, baseFiles[i]);
+                }
+                if (nullptr == comparisonFileBits) {
+                    drp->fComparison.fStatus = DiffResource::kCouldNotRead_Status;
+                    VERBOSE_STATUS("READ FAIL", ANSI_COLOR_RED, comparisonFiles[j]);
+                }
+                drp->fResult = DiffRecord::kCouldNotCompare_Result;
+
+            } else if (are_buffers_equal(baseFileBits.get(), comparisonFileBits.get())) {
+                drp->fResult = DiffRecord::kEqualBits_Result;
+                VERBOSE_STATUS("MATCH", ANSI_COLOR_GREEN, baseFiles[i]);
+            } else {
+                AutoReleasePixels arp(drp);
+                get_bitmap(baseFileBits, drp->fBase, false);
+                get_bitmap(comparisonFileBits, drp->fComparison, false);
+                VERBOSE_STATUS("DIFFERENT", ANSI_COLOR_RED, baseFiles[i]);
+                if (DiffResource::kDecoded_Status == drp->fBase.fStatus &&
+                    DiffResource::kDecoded_Status == drp->fComparison.fStatus) {
+                    create_and_write_diff_image(drp, dmp, colorThreshold,
+                                                outputDir, drp->fBase.fFilename);
+                } else {
+                    drp->fResult = DiffRecord::kCouldNotCompare_Result;
+                }
+            }
+
+            ++i;
+            ++j;
+        }
+
+        if (getBounds) {
+            get_bounds(*drp);
+        }
+        SkASSERT(DiffRecord::kUnknown_Result != drp->fResult);
+        differences->push(drp);
+        summary->add(drp);
+    }
+
+    for (; i < baseFiles.count(); ++i) {
+        // files only in baseDir
+        DiffRecord *drp = new DiffRecord();
+        drp->fBase.fFilename = *baseFiles[i];
+        drp->fBase.fFullPath = baseDir;
+        drp->fBase.fFullPath.append(drp->fBase.fFilename);
+        drp->fBase.fStatus = DiffResource::kExists_Status;
+
+        drp->fComparison.fFilename = *baseFiles[i];
+        drp->fComparison.fFullPath = comparisonDir;
+        drp->fComparison.fFullPath.append(drp->fComparison.fFilename);
+        drp->fComparison.fStatus = DiffResource::kDoesNotExist_Status;
+
+        drp->fResult = DiffRecord::kCouldNotCompare_Result;
+        if (getBounds) {
+            get_bounds(*drp);
+        }
+        differences->push(drp);
+        summary->add(drp);
+    }
+
+    for (; j < comparisonFiles.count(); ++j) {
+        // files only in comparisonDir
+        DiffRecord *drp = new DiffRecord();
+        drp->fBase.fFilename = *comparisonFiles[j];
+        drp->fBase.fFullPath = baseDir;
+        drp->fBase.fFullPath.append(drp->fBase.fFilename);
+        drp->fBase.fStatus = DiffResource::kDoesNotExist_Status;
+
+        drp->fComparison.fFilename = *comparisonFiles[j];
+        drp->fComparison.fFullPath = comparisonDir;
+        drp->fComparison.fFullPath.append(drp->fComparison.fFilename);
+        drp->fComparison.fStatus = DiffResource::kExists_Status;
+
+        drp->fResult = DiffRecord::kCouldNotCompare_Result;
+        if (getBounds) {
+            get_bounds(*drp);
+        }
+        differences->push(drp);
+        summary->add(drp);
+    }
+
+    release_file_list(&baseFiles);
+    release_file_list(&comparisonFiles);
+}
+
+static void usage (char * argv0) {
+    SkDebugf("Skia baseline image diff tool\n");
+    SkDebugf("\n"
+"Usage: \n"
+"    %s <baseDir> <comparisonDir> [outputDir] \n", argv0);
+    SkDebugf(
+"\nArguments:"
+"\n    --failonresult <result>: After comparing all file pairs, exit with nonzero"
+"\n                             return code (number of file pairs yielding this"
+"\n                             result) if any file pairs yielded this result."
+"\n                             This flag may be repeated, in which case the"
+"\n                             return code will be the number of fail pairs"
+"\n                             yielding ANY of these results."
+"\n    --failonstatus <baseStatus> <comparisonStatus>: exit with nonzero return"
+"\n                             code if any file pairs yielded this status."
+"\n    --help: display this info"
+"\n    --listfilenames: list all filenames for each result type in stdout"
+"\n    --match <substring>: compare files whose filenames contain this substring;"
+"\n                         if unspecified, compare ALL files."
+"\n                         this flag may be repeated."
+"\n    --nodiffs: don't write out image diffs or index.html, just generate"
+"\n               report on stdout"
+"\n    --nomatch <substring>: regardless of --match, DO NOT compare files whose"
+"\n                           filenames contain this substring."
+"\n                           this flag may be repeated."
+"\n    --noprintdirs: do not print the directories used."
+"\n    --norecurse: do not recurse into subdirectories."
+"\n    --sortbymaxmismatch: sort by worst color channel mismatch;"
+"\n                         break ties with -sortbymismatch"
+"\n    --sortbymismatch: sort by average color channel mismatch"
+"\n    --threshold <n>: only report differences > n (per color channel) [default 0]"
+"\n    --weighted: sort by # pixels different weighted by color difference"
+"\n"
+"\n    baseDir: directory to read baseline images from."
+"\n    comparisonDir: directory to read comparison images from"
+"\n    outputDir: directory to write difference images and index.html to;"
+"\n               defaults to comparisonDir"
+"\n"
+"\nIf no sort is specified, it will sort by fraction of pixels mismatching."
+"\n");
+}
+
+const int kNoError = 0;
+const int kGenericError = -1;
+
+int tool_main(int argc, char** argv);
+int tool_main(int argc, char** argv) {
+    DiffMetricProc diffProc = compute_diff_pmcolor;
+    int (*sortProc)(const void*, const void*) = compare<CompareDiffMetrics>;
+
+    // Maximum error tolerated in any one color channel in any one pixel before
+    // a difference is reported.
+    int colorThreshold = 0;
+    SkString baseDir;
+    SkString comparisonDir;
+    SkString outputDir;
+
+    StringArray matchSubstrings;
+    StringArray nomatchSubstrings;
+
+    bool generateDiffs = true;
+    bool listFilenames = false;
+    bool printDirNames = true;
+    bool recurseIntoSubdirs = true;
+    bool verbose = false;
+    bool listFailingBase = false;
+
+    RecordArray differences;
+    DiffSummary summary;
+
+    bool failOnResultType[DiffRecord::kResultCount];
+    for (int i = 0; i < DiffRecord::kResultCount; i++) {
+        failOnResultType[i] = false;
+    }
+
+    bool failOnStatusType[DiffResource::kStatusCount][DiffResource::kStatusCount];
+    for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+        for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+            failOnStatusType[base][comparison] = false;
+        }
+    }
+
+    int i;
+    int numUnflaggedArguments = 0;
+    for (i = 1; i < argc; i++) {
+        if (!strcmp(argv[i], "--failonresult")) {
+            if (argc == ++i) {
+                SkDebugf("failonresult expects one argument.\n");
+                continue;
+            }
+            DiffRecord::Result type = DiffRecord::getResultByName(argv[i]);
+            if (type != DiffRecord::kResultCount) {
+                failOnResultType[type] = true;
+            } else {
+                SkDebugf("ignoring unrecognized result <%s>\n", argv[i]);
+            }
+            continue;
+        }
+        if (!strcmp(argv[i], "--failonstatus")) {
+            if (argc == ++i) {
+                SkDebugf("failonstatus missing base status.\n");
+                continue;
+            }
+            bool baseStatuses[DiffResource::kStatusCount];
+            if (!DiffResource::getMatchingStatuses(argv[i], baseStatuses)) {
+                SkDebugf("unrecognized base status <%s>\n", argv[i]);
+            }
+
+            if (argc == ++i) {
+                SkDebugf("failonstatus missing comparison status.\n");
+                continue;
+            }
+            bool comparisonStatuses[DiffResource::kStatusCount];
+            if (!DiffResource::getMatchingStatuses(argv[i], comparisonStatuses)) {
+                SkDebugf("unrecognized comarison status <%s>\n", argv[i]);
+            }
+
+            for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+                for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+                    failOnStatusType[base][comparison] |=
+                        baseStatuses[base] && comparisonStatuses[comparison];
+                }
+            }
+            continue;
+        }
+        if (!strcmp(argv[i], "--help")) {
+            usage(argv[0]);
+            return kNoError;
+        }
+        if (!strcmp(argv[i], "--listfilenames")) {
+            listFilenames = true;
+            continue;
+        }
+        if (!strcmp(argv[i], "--verbose")) {
+            verbose = true;
+            continue;
+        }
+        if (!strcmp(argv[i], "--match")) {
+            matchSubstrings.push(new SkString(argv[++i]));
+            continue;
+        }
+        if (!strcmp(argv[i], "--nodiffs")) {
+            generateDiffs = false;
+            continue;
+        }
+        if (!strcmp(argv[i], "--nomatch")) {
+            nomatchSubstrings.push(new SkString(argv[++i]));
+            continue;
+        }
+        if (!strcmp(argv[i], "--noprintdirs")) {
+            printDirNames = false;
+            continue;
+        }
+        if (!strcmp(argv[i], "--norecurse")) {
+            recurseIntoSubdirs = false;
+            continue;
+        }
+        if (!strcmp(argv[i], "--sortbymaxmismatch")) {
+            sortProc = compare<CompareDiffMaxMismatches>;
+            continue;
+        }
+        if (!strcmp(argv[i], "--sortbymismatch")) {
+            sortProc = compare<CompareDiffMeanMismatches>;
+            continue;
+        }
+        if (!strcmp(argv[i], "--threshold")) {
+            colorThreshold = atoi(argv[++i]);
+            continue;
+        }
+        if (!strcmp(argv[i], "--weighted")) {
+            sortProc = compare<CompareDiffWeighted>;
+            continue;
+        }
+        if (argv[i][0] != '-') {
+            switch (numUnflaggedArguments++) {
+                case 0:
+                    baseDir.set(argv[i]);
+                    continue;
+                case 1:
+                    comparisonDir.set(argv[i]);
+                    continue;
+                case 2:
+                    outputDir.set(argv[i]);
+                    continue;
+                default:
+                    SkDebugf("extra unflagged argument <%s>\n", argv[i]);
+                    usage(argv[0]);
+                    return kGenericError;
+            }
+        }
+        if (!strcmp(argv[i], "--listFailingBase")) {
+            listFailingBase = true;
+            continue;
+        }
+
+        SkDebugf("Unrecognized argument <%s>\n", argv[i]);
+        usage(argv[0]);
+        return kGenericError;
+    }
+
+    if (numUnflaggedArguments == 2) {
+        outputDir = comparisonDir;
+    } else if (numUnflaggedArguments != 3) {
+        usage(argv[0]);
+        return kGenericError;
+    }
+
+    if (!baseDir.endsWith(PATH_DIV_STR)) {
+        baseDir.append(PATH_DIV_STR);
+    }
+    if (printDirNames) {
+        printf("baseDir is [%s]\n", baseDir.c_str());
+    }
+
+    if (!comparisonDir.endsWith(PATH_DIV_STR)) {
+        comparisonDir.append(PATH_DIV_STR);
+    }
+    if (printDirNames) {
+        printf("comparisonDir is [%s]\n", comparisonDir.c_str());
+    }
+
+    if (!outputDir.endsWith(PATH_DIV_STR)) {
+        outputDir.append(PATH_DIV_STR);
+    }
+    if (generateDiffs) {
+        if (printDirNames) {
+            printf("writing diffs to outputDir is [%s]\n", outputDir.c_str());
+        }
+    } else {
+        if (printDirNames) {
+            printf("not writing any diffs to outputDir [%s]\n", outputDir.c_str());
+        }
+        outputDir.set("");
+    }
+
+    // If no matchSubstrings were specified, match ALL strings
+    // (except for whatever nomatchSubstrings were specified, if any).
+    if (matchSubstrings.isEmpty()) {
+        matchSubstrings.push(new SkString(""));
+    }
+
+    create_diff_images(diffProc, colorThreshold, &differences,
+                       baseDir, comparisonDir, outputDir,
+                       matchSubstrings, nomatchSubstrings, recurseIntoSubdirs, generateDiffs,
+                       verbose, &summary);
+    summary.print(listFilenames, failOnResultType, failOnStatusType);
+
+    if (listFailingBase) {
+        summary.printfFailingBaseNames("\n");
+    }
+
+    if (differences.count()) {
+        qsort(differences.begin(), differences.count(),
+              sizeof(DiffRecord*), sortProc);
+    }
+
+    if (generateDiffs) {
+        print_diff_page(summary.fNumMatches, colorThreshold, differences,
+                        baseDir, comparisonDir, outputDir);
+    }
+
+    for (i = 0; i < differences.count(); i++) {
+        delete differences[i];
+    }
+    matchSubstrings.deleteAll();
+    nomatchSubstrings.deleteAll();
+
+    int num_failing_results = 0;
+    for (int i = 0; i < DiffRecord::kResultCount; i++) {
+        if (failOnResultType[i]) {
+            num_failing_results += summary.fResultsOfType[i].count();
+        }
+    }
+    if (!failOnResultType[DiffRecord::kCouldNotCompare_Result]) {
+        for (int base = 0; base < DiffResource::kStatusCount; ++base) {
+            for (int comparison = 0; comparison < DiffResource::kStatusCount; ++comparison) {
+                if (failOnStatusType[base][comparison]) {
+                    num_failing_results += summary.fStatusOfType[base][comparison].count();
+                }
+            }
+        }
+    }
+
+    // On Linux (and maybe other platforms too), any results outside of the
+    // range [0...255] are wrapped (mod 256).  Do the conversion ourselves, to
+    // make sure that we only return 0 when there were no failures.
+    return (num_failing_results > 255) ? 255 : num_failing_results;
+}
+
+#if !defined SK_BUILD_FOR_IOS
+int main(int argc, char * const argv[]) {
+    return tool_main(argc, (char**) argv);
+}
+#endif
diff --git a/tools/skdiff/skdiff_utils.cpp b/tools/skdiff/skdiff_utils.cpp
new file mode 100644
index 0000000000..609d75d265
--- /dev/null
+++ b/tools/skdiff/skdiff_utils.cpp
@@ -0,0 +1,179 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "skdiff.h"
+#include "skdiff_utils.h"
+#include "SkBitmap.h"
+#include "SkCodec.h"
+#include "SkData.h"
+#include "SkImageEncoder.h"
+#include "SkStream.h"
+#include "SkTypes.h"
+
+#include <memory>
+
+bool are_buffers_equal(SkData* skdata1, SkData* skdata2) {
+    if ((nullptr == skdata1) || (nullptr == skdata2)) {
+        return false;
+    }
+    if (skdata1->size() != skdata2->size()) {
+        return false;
+    }
+    return (0 == memcmp(skdata1->data(), skdata2->data(), skdata1->size()));
+}
+
+sk_sp<SkData> read_file(const char* file_path) {
+    sk_sp<SkData> data(SkData::MakeFromFileName(file_path));
+    if (!data) {
+        SkDebugf("WARNING: could not open file <%s> for reading\n", file_path);
+    }
+    return data;
+}
+
+bool get_bitmap(sk_sp<SkData> fileBits, DiffResource& resource, bool sizeOnly) {
+    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromData(fileBits));
+    if (!codec) {
+        SkDebugf("ERROR: could not create codec for <%s>\n", resource.fFullPath.c_str());
+        resource.fStatus = DiffResource::kCouldNotDecode_Status;
+        return false;
+    }
+
+    if (!resource.fBitmap.setInfo(codec->getInfo().makeColorType(kN32_SkColorType))) {
+        SkDebugf("ERROR: could not set bitmap info for <%s>\n", resource.fFullPath.c_str());
+        resource.fStatus = DiffResource::kCouldNotDecode_Status;
+        return false;
+    }
+
+    if (sizeOnly) {
+        return true;
+    }
+
+    if (!resource.fBitmap.tryAllocPixels()) {
+        SkDebugf("ERROR: could not allocate pixels for <%s>\n", resource.fFullPath.c_str());
+        resource.fStatus = DiffResource::kCouldNotDecode_Status;
+        return false;
+    }
+
+    if (SkCodec::kSuccess != codec->getPixels(resource.fBitmap.info(),
+            resource.fBitmap.getPixels(), resource.fBitmap.rowBytes())) {
+        SkDebugf("ERROR: codec failed for basePath <%s>\n", resource.fFullPath.c_str());
+        resource.fStatus = DiffResource::kCouldNotDecode_Status;
+        return false;
+    }
+
+    resource.fStatus = DiffResource::kDecoded_Status;
+    return true;
+}
+
+/** Thanks to PNG, we need to force all pixels 100% opaque. */
+static void force_all_opaque(const SkBitmap& bitmap) {
+   SkAutoLockPixels lock(bitmap);
+   for (int y = 0; y < bitmap.height(); y++) {
+       for (int x = 0; x < bitmap.width(); x++) {
+           *bitmap.getAddr32(x, y) |= (SK_A32_MASK << SK_A32_SHIFT);
+       }
+   }
+}
+
+bool write_bitmap(const SkString& path, const SkBitmap& bitmap) {
+    SkBitmap copy;
+    bitmap.copyTo(&copy, kN32_SkColorType);
+    force_all_opaque(copy);
+    return SkImageEncoder::EncodeFile(path.c_str(), copy,
+                                      SkImageEncoder::kPNG_Type, 100);
+}
+
+/// Return a copy of the "input" string, within which we have replaced all instances
+/// of oldSubstring with newSubstring.
+///
+/// TODO: If we like this, we should move it into the core SkString implementation,
+/// adding more checks and ample test cases, and paying more attention to efficiency.
+static SkString replace_all(const SkString &input,
+                            const char oldSubstring[], const char newSubstring[]) {
+    SkString output;
+    const char *input_cstr = input.c_str();
+    const char *first_char = input_cstr;
+    const char *match_char;
+    size_t oldSubstringLen = strlen(oldSubstring);
+    while ((match_char = strstr(first_char, oldSubstring))) {
+        output.append(first_char, (match_char - first_char));
+        output.append(newSubstring);
+        first_char = match_char + oldSubstringLen;
+    }
+    output.append(first_char);
+    return output;
+}
+
+static SkString filename_to_derived_filename(const SkString& filename, const char *suffix) {
+    SkString diffName (filename);
+    const char* cstring = diffName.c_str();
+    size_t dotOffset = strrchr(cstring, '.') - cstring;
+    diffName.remove(dotOffset, diffName.size() - dotOffset);
+    diffName.append(suffix);
+
+    // In case we recursed into subdirectories, replace slashes with something else
+    // so the diffs will all be written into a single flat directory.
+    diffName = replace_all(diffName, PATH_DIV_STR, "_");
+    return diffName;
+}
+
+SkString filename_to_diff_filename(const SkString& filename) {
+    return filename_to_derived_filename(filename, "-diff.png");
+}
+
+SkString filename_to_white_filename(const SkString& filename) {
+    return filename_to_derived_filename(filename, "-white.png");
+}
+
+void create_and_write_diff_image(DiffRecord* drp,
+                                 DiffMetricProc dmp,
+                                 const int colorThreshold,
+                                 const SkString& outputDir,
+                                 const SkString& filename) {
+    const int w = drp->fBase.fBitmap.width();
+    const int h = drp->fBase.fBitmap.height();
+
+    if (w != drp->fComparison.fBitmap.width() || h != drp->fComparison.fBitmap.height()) {
+        drp->fResult = DiffRecord::kDifferentSizes_Result;
+    } else {
+        drp->fDifference.fBitmap.allocN32Pixels(w, h);
+
+        drp->fWhite.fBitmap.allocN32Pixels(w, h);
+
+        SkASSERT(DiffRecord::kUnknown_Result == drp->fResult);
+        compute_diff(drp, dmp, colorThreshold);
+        SkASSERT(DiffRecord::kUnknown_Result != drp->fResult);
+    }
+
+    if (outputDir.isEmpty()) {
+        drp->fDifference.fStatus = DiffResource::kUnspecified_Status;
+        drp->fWhite.fStatus = DiffResource::kUnspecified_Status;
+
+    } else {
+        drp->fDifference.fFilename = filename_to_diff_filename(filename);
+        drp->fDifference.fFullPath = outputDir;
+        drp->fDifference.fFullPath.append(drp->fDifference.fFilename);
+        drp->fDifference.fStatus = DiffResource::kSpecified_Status;
+
+        drp->fWhite.fFilename = filename_to_white_filename(filename);
+        drp->fWhite.fFullPath = outputDir;
+        drp->fWhite.fFullPath.append(drp->fWhite.fFilename);
+        drp->fWhite.fStatus = DiffResource::kSpecified_Status;
+
+        if (DiffRecord::kDifferentPixels_Result == drp->fResult) {
+            if (write_bitmap(drp->fDifference.fFullPath, drp->fDifference.fBitmap)) {
+                drp->fDifference.fStatus = DiffResource::kExists_Status;
+            } else {
+                drp->fDifference.fStatus = DiffResource::kDoesNotExist_Status;
+            }
+            if (write_bitmap(drp->fWhite.fFullPath, drp->fWhite.fBitmap)) {
+                drp->fWhite.fStatus = DiffResource::kExists_Status;
+            } else {
+                drp->fWhite.fStatus = DiffResource::kDoesNotExist_Status;
+            }
+        }
+    }
+}
diff --git a/tools/skdiff/skdiff_utils.h b/tools/skdiff/skdiff_utils.h
new file mode 100644
index 0000000000..c799325e36
--- /dev/null
+++ b/tools/skdiff/skdiff_utils.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef skdiff_utils_DEFINED
+#define skdiff_utils_DEFINED
+
+#include "skdiff.h"
+
+class SkBitmap;
+class SkData;
+class SkString;
+
+/** Returns true if the two buffers passed in are both non-nullptr,
+ *  have the same length, and contain exactly the same byte values.
+ */
+bool are_buffers_equal(SkData* skdata1, SkData* skdata2);
+
+/** Reads the file at the given path and returns its complete contents as an
+ *  SkData object (or returns nullptr on error).
+ */
+sk_sp<SkData> read_file(const char* file_path);
+
+/** Decodes the fileBits into the resource.fBitmap. Returns false on failure. */
+bool get_bitmap(sk_sp<SkData> fileBits, DiffResource& resource, bool sizeOnly);
+
+/** Writes the bitmap as a PNG to the path specified. */
+bool write_bitmap(const SkString& path, const SkBitmap& bitmap);
+
+/** Given an image filename, returns the name of the file containing
+ *  the associated difference image.
+ */
+SkString filename_to_diff_filename(const SkString& filename);
+
+/** Given an image filename, returns the name of the file containing
+ *  the "white" difference image.
+ */
+SkString filename_to_white_filename(const SkString& filename);
+
+/** Calls compute_diff and handles the difference and white diff resources.
+ *  If !outputDir.isEmpty(), writes out difference and white images.
+ */
+void create_and_write_diff_image(DiffRecord* drp,
+                                 DiffMetricProc dmp,
+                                 const int colorThreshold,
+                                 const SkString& outputDir,
+                                 const SkString& filename);
+
+#endif