Revert of allow one zero length dash (patchset #8 id:140001 of https://codereview.chromium.org/1805963002/ )

Reason for revert:
Causes the dash bench to crash.

Example crash:
https://build.chromium.org/p/client.skia/builders/Perf-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release/builds/5581/steps/nanobench/logs/stdio

Original issue's description:
> allow one zero length dash
>
> If the constructed stroke that represents a dash has a
> single dash of length zero, and the end cap is square or
> round, draw the cap.
>
> The old code initialized the initial dash length to zero,
> making it ambiguous whether the first length is zero or
> not.
>
> R=robertphillips@google.com
> BUG=583299
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1805963002
>
> Committed: https://skia.googlesource.com/skia/+/5e1a24808415df2748822e8082e21a361362cdfe

TBR=robertphillips@google.com,reed@google.com,caryclark@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=583299

Review URL: https://codereview.chromium.org/1808303004

6 files changed, 59 insertions, 89 deletions

diff --git a/gm/arcto.cpp b/gm/arcto.cpp
index 584fca3c4f..cd26eef35a 100644
--- a/gm/arcto.cpp
+++ b/gm/arcto.cpp
@@ -205,24 +205,3 @@ DEF_SIMPLE_GM(bug593049, canvas, 300, 300) {
 
     canvas->drawPath(p, paint);
 }
-
-#include "SkDashPathEffect.h"
-#include "SkPathMeasure.h"
-
-DEF_SIMPLE_GM(bug583299, canvas, 300, 300) {
-  const char* d="M60,60 A50,50 0 0 0 160,60 A50,50 0 0 0 60,60z";
-  SkPaint p;
-  p.setStyle(SkPaint::kStroke_Style);
-  p.setStrokeWidth(100);
-  p.setAntiAlias(true);
-  p.setColor(0xFF008200);
-  p.setStrokeCap(SkPaint::kSquare_Cap);
-  SkPath path;
-  SkParsePath::FromSVGString(d, &path);
-  SkPathMeasure meas(path, false);
-  SkScalar length = meas.getLength();
-  SkScalar intervals[] = {0, length };
-  int intervalCount = (int) SK_ARRAY_COUNT(intervals);
-  p.setPathEffect(SkDashPathEffect::Create(intervals, intervalCount, 0))->unref();
-  canvas->drawPath(path, p);
-}
diff --git a/gm/dashing.cpp b/gm/dashing.cpp
index c728d15a1a..dfd1b629c1 100644
--- a/gm/dashing.cpp
+++ b/gm/dashing.cpp
@@ -21,8 +21,7 @@ static void drawline(SkCanvas* canvas, int on, int off, const SkPaint& paint,
         SkIntToScalar(off),
     };
 
-    SkAutoTUnref<SkPathEffect> effect(SkDashPathEffect::Create(intervals, 2, phase));
-    p.setPathEffect(effect);
+    p.setPathEffect(SkDashPathEffect::Create(intervals, 2, phase))->unref();
     canvas->drawLine(startX, startY, finalX, finalY, p);
 }
 
diff --git a/src/effects/SkDashPathEffect.cpp b/src/effects/SkDashPathEffect.cpp
index 3816499915..ced0aab69a 100644
--- a/src/effects/SkDashPathEffect.cpp
+++ b/src/effects/SkDashPathEffect.cpp
@@ -14,7 +14,7 @@
 
 SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, SkScalar phase)
         : fPhase(0)
-        , fInitialDashLength(-1)
+        , fInitialDashLength(0)
         , fInitialDashIndex(0)
         , fIntervalLength(0) {
     SkASSERT(intervals);
@@ -23,6 +23,7 @@ SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, SkScal
     fIntervals = (SkScalar*)sk_malloc_throw(sizeof(SkScalar) * count);
     fCount = count;
     for (int i = 0; i < count; i++) {
+        SkASSERT(intervals[i] >= 0);
         fIntervals[i] = intervals[i];
     }
 
@@ -37,7 +38,7 @@ SkDashPathEffect::~SkDashPathEffect() {
 
 bool SkDashPathEffect::filterPath(SkPath* dst, const SkPath& src,
                               SkStrokeRec* rec, const SkRect* cullRect) const {
-    return SkDashPath::InternalFilter(dst, src, rec, cullRect, fIntervals, fCount,
+    return SkDashPath::FilterDashPath(dst, src, rec, cullRect, fIntervals, fCount,
                                       fInitialDashLength, fInitialDashIndex, fIntervalLength);
 }
 
@@ -161,7 +162,7 @@ bool SkDashPathEffect::asPoints(PointData* results,
                                 const SkMatrix& matrix,
                                 const SkRect* cullRect) const {
     // width < 0 -> fill && width == 0 -> hairline so requiring width > 0 rules both out
-    if (0 >= rec.getWidth()) {
+    if (fInitialDashLength < 0 || 0 >= rec.getWidth()) {
         return false;
     }
 
@@ -387,8 +388,13 @@ void SkDashPathEffect::toString(SkString* str) const {
 //////////////////////////////////////////////////////////////////////////////////////////////////
 
 SkPathEffect* SkDashPathEffect::Create(const SkScalar intervals[], int count, SkScalar phase) {
-    if (!SkDashPath::ValidDashPath(phase, intervals, count)) {
+    if ((count < 2) || !SkIsAlign2(count)) {
         return nullptr;
     }
+    for (int i = 0; i < count; i++) {
+        if (intervals[i] < 0) {
+            return nullptr;
+        }
+    }
     return new SkDashPathEffect(intervals, count, phase);
 }
diff --git a/src/utils/SkDashPath.cpp b/src/utils/SkDashPath.cpp
index d766b0d53e..0d2783eba2 100644
--- a/src/utils/SkDashPath.cpp
+++ b/src/utils/SkDashPath.cpp
@@ -40,35 +40,42 @@ void SkDashPath::CalcDashParameters(SkScalar phase, const SkScalar intervals[],
         len += intervals[i];
     }
     *intervalLength = len;
-    // Adjust phase to be between 0 and len, "flipping" phase if negative.
-    // e.g., if len is 100, then phase of -20 (or -120) is equivalent to 80
-    if (adjustedPhase) {
-        if (phase < 0) {
-            phase = -phase;
-            if (phase > len) {
+
+    // watch out for values that might make us go out of bounds
+    if ((len > 0) && SkScalarIsFinite(phase) && SkScalarIsFinite(len)) {
+
+        // Adjust phase to be between 0 and len, "flipping" phase if negative.
+        // e.g., if len is 100, then phase of -20 (or -120) is equivalent to 80
+        if (adjustedPhase) {
+            if (phase < 0) {
+                phase = -phase;
+                if (phase > len) {
+                    phase = SkScalarMod(phase, len);
+                }
+                phase = len - phase;
+
+                // Due to finite precision, it's possible that phase == len,
+                // even after the subtract (if len >>> phase), so fix that here.
+                // This fixes http://crbug.com/124652 .
+                SkASSERT(phase <= len);
+                if (phase == len) {
+                    phase = 0;
+                }
+            } else if (phase >= len) {
                 phase = SkScalarMod(phase, len);
             }
-            phase = len - phase;
-
-            // Due to finite precision, it's possible that phase == len,
-            // even after the subtract (if len >>> phase), so fix that here.
-            // This fixes http://crbug.com/124652 .
-            SkASSERT(phase <= len);
-            if (phase == len) {
-                phase = 0;
-            }
-        } else if (phase >= len) {
-            phase = SkScalarMod(phase, len);
+            *adjustedPhase = phase;
         }
-        *adjustedPhase = phase;
-    }
-    SkASSERT(phase >= 0 && phase < len);
+        SkASSERT(phase >= 0 && phase < len);
 
-    *initialDashLength = find_first_interval(intervals, phase,
-                                            initialDashIndex, count);
+        *initialDashLength = find_first_interval(intervals, phase,
+                                                initialDashIndex, count);
 
-    SkASSERT(*initialDashLength >= 0);
-    SkASSERT(*initialDashIndex >= 0 && *initialDashIndex < count);
+        SkASSERT(*initialDashLength >= 0);
+        SkASSERT(*initialDashIndex >= 0 && *initialDashIndex < count);
+    } else {
+        *initialDashLength = -1;    // signal bad dash intervals
+    }
 }
 
 static void outset_for_stroke(SkRect* rect, const SkStrokeRec& rec) {
@@ -213,13 +220,13 @@ private:
 };
 
 
-bool SkDashPath::InternalFilter(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
+bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
                                 const SkRect* cullRect, const SkScalar aIntervals[],
                                 int32_t count, SkScalar initialDashLength, int32_t initialDashIndex,
                                 SkScalar intervalLength) {
 
-    // we do nothing if the src wants to be filled
-    if (rec->isFillStyle()) {
+    // we do nothing if the src wants to be filled, or if our dashlength is 0
+    if (rec->isFillStyle() || initialDashLength < 0) {
         return false;
     }
 
@@ -299,7 +306,7 @@ bool SkDashPath::InternalFilter(SkPath* dst, const SkPath& src, SkStrokeRec* rec
 
         // extend if we ended on a segment and we need to join up with the (skipped) initial segment
         if (meas.isClosed() && is_even(initialDashIndex) &&
-            initialDashLength >= 0) {
+            initialDashLength > 0) {
             meas.getSegment(0, initialDashLength, dst, !addedSegment);
             ++segCount;
         }
@@ -314,29 +321,11 @@ bool SkDashPath::InternalFilter(SkPath* dst, const SkPath& src, SkStrokeRec* rec
 
 bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
                                 const SkRect* cullRect, const SkPathEffect::DashInfo& info) {
-    if (!ValidDashPath(info.fPhase, info.fIntervals, info.fCount)) {
-        return false;
-    }
     SkScalar initialDashLength = 0;
     int32_t initialDashIndex = 0;
     SkScalar intervalLength = 0;
     CalcDashParameters(info.fPhase, info.fIntervals, info.fCount,
                        &initialDashLength, &initialDashIndex, &intervalLength);
-    return InternalFilter(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength,
+    return FilterDashPath(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength,
                           initialDashIndex, intervalLength);
 }
-
-bool SkDashPath::ValidDashPath(SkScalar phase, const SkScalar intervals[], int32_t count) {
-    if (count < 2 || !SkIsAlign2(count)) {
-        return false;
-    }
-    SkScalar length = 0;
-    for (int i = 0; i < count; i++) {
-        if (intervals[i] < 0) {
-            return false;
-        }
-        length += intervals[i];
-    }
-    // watch out for values that might make us go out of bounds
-    return length > 0 && SkScalarIsFinite(phase) && SkScalarIsFinite(length);
-}
diff --git a/src/utils/SkDashPathPriv.h b/src/utils/SkDashPathPriv.h
index 54bf9a4870..7453dcec82 100644
--- a/src/utils/SkDashPathPriv.h
+++ b/src/utils/SkDashPathPriv.h
@@ -16,25 +16,17 @@ namespace SkDashPath {
      * inputed phase and intervals. If adjustedPhase is passed in, then the phase will be
      * adjusted to be between 0 and intervalLength. The result will be stored in adjustedPhase.
      * If adjustedPhase is nullptr then it is assumed phase is already between 0 and intervalLength
-     *
-     * Caller should have already used ValidDashPath to exclude invalid data.
      */
     void CalcDashParameters(SkScalar phase, const SkScalar intervals[], int32_t count,
                             SkScalar* initialDashLength, int32_t* initialDashIndex,
                             SkScalar* intervalLength, SkScalar* adjustedPhase = nullptr);
 
     bool FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec*, const SkRect*,
+                        const SkScalar aIntervals[], int32_t count, SkScalar initialDashLength,
+                        int32_t initialDashIndex, SkScalar intervalLength);
+    
+    bool FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec*, const SkRect*,
                         const SkPathEffect::DashInfo& info);
-
-    /*
-     * Caller should have already used ValidDashPath to exclude invalid data.
-     */
-    bool InternalFilter(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
-                        const SkRect* cullRect, const SkScalar aIntervals[],
-                        int32_t count, SkScalar initialDashLength, int32_t initialDashIndex,
-                        SkScalar intervalLength);
-
-    bool ValidDashPath(SkScalar phase, const SkScalar intervals[], int32_t count);
 }
 
 #endif
diff --git a/tests/DashPathEffectTest.cpp b/tests/DashPathEffectTest.cpp
index fa2395ef75..68fce9a142 100644
--- a/tests/DashPathEffectTest.cpp
+++ b/tests/DashPathEffectTest.cpp
@@ -12,15 +12,20 @@
 #include "SkStrokeRec.h"
 
 // crbug.com/348821 was rooted in SkDashPathEffect refusing to flatten and unflatten itself when
-// the effect is nonsense.  Here we test that it fails when passed nonsense parameters.
+// fInitialDashLength < 0 (a signal the effect is nonsense).  Here we test that it flattens.
 
 DEF_TEST(DashPathEffectTest_crbug_348821, r) {
     SkScalar intervals[] = { 1.76934361e+36f, 2.80259693e-45f };  // Values from bug.
     const int count = 2;
-    SkScalar phase = SK_ScalarInfinity;  // Used to force a nonsense effect.
+    SkScalar phase = SK_ScalarInfinity;  // Used to force the bad fInitialDashLength = -1 path.
     SkAutoTUnref<SkPathEffect> dash(SkDashPathEffect::Create(intervals, count, phase));
 
-    REPORTER_ASSERT(r, dash == nullptr);
+    // nullptr -> refuses to work with flattening framework.
+    REPORTER_ASSERT(r, dash->getFactory() != nullptr);
+
+    SkWriteBuffer buffer;
+    buffer.writeFlattenable(dash);
+    REPORTER_ASSERT(r, buffer.bytesWritten() > 12);  // We'd write 12 if broken, >=40 if not.
 }
 
 // Test out the asPoint culling behavior.