Add SkAndroidCodec::computeSampledSize

Bug: b/63909536

Android's ImageDecoder API takes as input an arbitrary width and height
to scale the image to. Internally, this uses SkAndroidCodec to sample,
and then (if not a perfect match) scales to the desired size with
drawing.

computeSampledSize is a modified version of what ImageDecoder currently
does to convert from arbitrary dimensions to a sampleSize. Moving it
here allows it to be shared by SkAnimatedImage. The modified version
also corrects two bugs:
- a client using the dimensions returned by getSampledDimensions
  previously may have resulted in ImageDecoder decoding to a larger
  size and then scaling it. (example found in tests: dog.jpg is
  180 x 180. getSampledDimensions(8) returns 23 x 23, but the old
  method resulted in using sampleSize of 7 and downscaling the resulting
  25 x 25 image.)
- recompute the sampleSize based on the size returned by
  getSampledDimensions.

Change-Id: I022040e8bac31c20988903a0452257f7ae902bc7
Reviewed-on: https://skia-review.googlesource.com/94620
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>

4 files changed, 225 insertions, 0 deletions

diff --git a/gn/tests.gni b/gn/tests.gni
index a4054b8c01..18defe8ae1 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -7,6 +7,7 @@
 _tests = get_path_info("../tests", "abspath")
 
 tests_sources = [
+  "$_tests/AndroidCodecTest.cpp",
   "$_tests/AAClipTest.cpp",
   "$_tests/AnnotationTest.cpp",
   "$_tests/ApplyGammaTest.cpp",
diff --git a/include/codec/SkAndroidCodec.h b/include/codec/SkAndroidCodec.h
index 2bf38025bf..0746f066c8 100644
--- a/include/codec/SkAndroidCodec.h
+++ b/include/codec/SkAndroidCodec.h
@@ -91,6 +91,17 @@ public:
                                                 sk_sp<SkColorSpace> prefColorSpace = nullptr);
 
     /**
+     *  Compute the appropriate sample size to get to |size|.
+     *
+     *  @param size As an input parameter, the desired output size of
+     *      the decode. As an output parameter, the smallest sampled size
+     *      larger than the input.
+     *  @return the sample size to set AndroidOptions::fSampleSize to decode
+     *      to the output |size|.
+     */
+    int computeSampleSize(SkISize* size) const;
+
+    /**
      *  Returns the dimensions of the scaled output image, for an input
      *  sampleSize.
      *
diff --git a/src/codec/SkAndroidCodec.cpp b/src/codec/SkAndroidCodec.cpp
index a7ffa4e93b..486257f9a3 100644
--- a/src/codec/SkAndroidCodec.cpp
+++ b/src/codec/SkAndroidCodec.cpp
@@ -186,6 +186,100 @@ sk_sp<SkColorSpace> SkAndroidCodec::computeOutputColorSpace(SkColorType outputCo
     }
 }
 
+static bool supports_any_down_scale(const SkCodec* codec) {
+    return codec->getEncodedFormat() == SkEncodedImageFormat::kWEBP;
+}
+
+// There are a variety of ways two SkISizes could be compared. This method
+// returns true if either dimensions of a is < that of b.
+// computeSampleSize also uses the opposite, which means that both
+// dimensions of a >= b.
+static inline bool smaller_than(const SkISize& a, const SkISize& b) {
+    return a.width() < b.width() || a.height() < b.height();
+}
+
+// Both dimensions of a > that of b.
+static inline bool strictly_bigger_than(const SkISize& a, const SkISize& b) {
+    return a.width() > b.width() && a.height() > b.height();
+}
+
+int SkAndroidCodec::computeSampleSize(SkISize* desiredSize) const {
+    SkASSERT(desiredSize);
+
+    if (!desiredSize || *desiredSize == fInfo.dimensions()) {
+        return 1;
+    }
+
+    if (smaller_than(fInfo.dimensions(), *desiredSize)) {
+        *desiredSize = fInfo.dimensions();
+        return 1;
+    }
+
+    // Handle bad input:
+    if (desiredSize->width() < 1 || desiredSize->height() < 1) {
+        *desiredSize = SkISize::Make(std::max(1, desiredSize->width()),
+                                     std::max(1, desiredSize->height()));
+    }
+
+    if (supports_any_down_scale(fCodec.get())) {
+        return 1;
+    }
+
+    int sampleX = fInfo.width()  / desiredSize->width();
+    int sampleY = fInfo.height() / desiredSize->height();
+    int sampleSize = std::min(sampleX, sampleY);
+    auto computedSize = this->getSampledDimensions(sampleSize);
+    if (computedSize == *desiredSize) {
+        return sampleSize;
+    }
+
+    if (computedSize == fInfo.dimensions() || sampleSize == 1) {
+        // Cannot downscale
+        *desiredSize = computedSize;
+        return 1;
+    }
+
+    if (strictly_bigger_than(computedSize, *desiredSize)) {
+        // See if there is a tighter fit.
+        while (true) {
+            auto smaller = this->getSampledDimensions(sampleSize + 1);
+            if (smaller == *desiredSize) {
+                return sampleSize + 1;
+            }
+            if (smaller == computedSize || smaller_than(smaller, *desiredSize)) {
+                // Cannot get any smaller without being smaller than desired.
+                *desiredSize = computedSize;
+                return sampleSize;
+            }
+
+            sampleSize++;
+            computedSize = smaller;
+        }
+
+        SkASSERT(false);
+    }
+
+    if (!smaller_than(computedSize, *desiredSize)) {
+        // This means one of the computed dimensions is equal to desired, and
+        // the other is bigger. This is as close as we can get.
+        *desiredSize = computedSize;
+        return sampleSize;
+    }
+
+    // computedSize is too small. Make it larger.
+    while (sampleSize > 2) {
+        auto bigger = this->getSampledDimensions(sampleSize - 1);
+        if (bigger == *desiredSize || !smaller_than(bigger, *desiredSize)) {
+            *desiredSize = bigger;
+            return sampleSize - 1;
+        }
+        sampleSize--;
+    }
+
+    *desiredSize = fInfo.dimensions();
+    return 1;
+}
+
 SkISize SkAndroidCodec::getSampledDimensions(int sampleSize) const {
     if (!is_valid_sample_size(sampleSize)) {
         return {0, 0};
diff --git a/tests/AndroidCodecTest.cpp b/tests/AndroidCodecTest.cpp
new file mode 100644
index 0000000000..b86a210279
--- /dev/null
+++ b/tests/AndroidCodecTest.cpp
@@ -0,0 +1,119 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkAndroidCodec.h"
+#include "SkCodec.h"
+#include "SkEncodedImageFormat.h"
+
+#include "Resources.h"
+#include "Test.h"
+
+static SkISize times(const SkISize& size, float factor) {
+    return { (int) (size.width() * factor), (int) (size.height() * factor) };
+}
+
+static SkISize plus(const SkISize& size, int term) {
+    return { size.width() + term, size.height() + term };
+}
+
+static bool invalid(const SkISize& size) {
+    return size.width() < 1 || size.height() < 1;
+}
+
+DEF_TEST(AndroidCodec_computeSampleSize, r) {
+    if (GetResourcePath().isEmpty()) {
+        return;
+    }
+    for (const char* file : { "images/color_wheel.webp",
+                              "images/ship.png",
+                              "images/dog.jpg",
+                              "images/color_wheel.gif",
+                              "images/rle.bmp",
+                              "images/google_chrome.ico",
+                              "images/mandrill.wbmp",
+#ifdef SK_CODEC_DECODES_RAW
+                              "images/sample_1mp.dng",
+#endif
+                              }) {
+        auto data = GetResourceAsData(file);
+        if (!data) {
+            ERRORF(r, "Could not get %s", file);
+            continue;
+        }
+
+        auto codec = SkAndroidCodec::MakeFromCodec(SkCodec::MakeFromData(std::move(data)));
+        if (!codec) {
+            ERRORF(r, "Could not create codec for %s", file);
+            continue;
+        }
+
+        const auto dims = codec->getInfo().dimensions();
+        const SkISize downscales[] = {
+            plus(dims, -1),
+            times(dims, .15f),
+            times(dims, .6f),
+            { (int32_t) (dims.width() * .25f), (int32_t) (dims.height() * .75f ) },
+            { 1,  1 },
+            { 1,  2 },
+            { 2,  1 },
+            { 0, -1 },
+            { dims.width(), dims.height() - 1 },
+        };
+        for (SkISize size : downscales) {
+            const auto requested = size;
+            const int computedSampleSize = codec->computeSampleSize(&size);
+            REPORTER_ASSERT(r, size.width() >= 1 && size.height() >= 1);
+            if (codec->getEncodedFormat() == SkEncodedImageFormat::kWEBP) {
+                // WebP supports arbitrary down-scaling.
+                REPORTER_ASSERT(r, size == requested || invalid(requested));
+            } else if (computedSampleSize == 1) {
+                REPORTER_ASSERT(r, size == dims);
+            } else {
+                REPORTER_ASSERT(r, computedSampleSize > 1);
+                if (size.width() >= dims.width() || size.height() >= dims.height()) {
+                    ERRORF(r, "File %s's computed sample size (%i) is bigger than"
+                              " original? original: %i x %i\tsampled: %i x %i",
+                              file, computedSampleSize, dims.width(), dims.height(),
+                              size.width(), size.height());
+                }
+                REPORTER_ASSERT(r, size.width()  >= requested.width() &&
+                                   size.height() >= requested.height());
+                REPORTER_ASSERT(r, size.width()  <  dims.width() &&
+                                   size.height() <  dims.height());
+            }
+        }
+
+        const SkISize upscales[] = {
+            dims, plus(dims, 5), times(dims, 2),
+        };
+        for (SkISize size : upscales) {
+            const int computedSampleSize = codec->computeSampleSize(&size);
+            REPORTER_ASSERT(r, computedSampleSize == 1);
+            REPORTER_ASSERT(r, dims == size);
+        }
+
+        // This mimics how Android's ImageDecoder uses SkAndroidCodec. A client
+        // can choose their dimensions based on calling getSampledDimensions,
+        // but the ImageDecoder API takes an arbitrary size. It then uses
+        // computeSampleSize to determine the best dimensions and sampleSize.
+        // It should return the same dimensions. the sampleSize may be different
+        // due to integer division.
+        for (int sampleSize : { 1, 2, 3, 4, 8, 16, 32 }) {
+            const SkISize sampledDims = codec->getSampledDimensions(sampleSize);
+            SkISize size = sampledDims;
+            const int computedSampleSize = codec->computeSampleSize(&size);
+            if (sampledDims != size) {
+                ERRORF(r, "File '%s'->getSampledDimensions(%i) yields computed"
+                          " sample size of %i\n\tsampledDimensions: %i x %i\t"
+                          "computed dimensions: %i x %i",
+                          file, sampleSize, computedSampleSize,
+                          sampledDims.width(), sampledDims.height(),
+                          size.width(), size.height());
+            }
+        }
+    }
+}