2 files changed, 54 insertions, 31 deletions

diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index bf12ad2625..d9992c0cd9 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -208,16 +208,37 @@ bool SkCodec::rewindIfNeeded() {
     return this->onRewind();
 }
 
-static void zero_rect(const SkImageInfo& dstInfo, void* pixels, size_t rowBytes,
-                      SkIRect frameRect) {
-    if (!frameRect.intersect(dstInfo.bounds())) {
-        return;
+bool zero_rect(const SkImageInfo& dstInfo, void* pixels, size_t rowBytes,
+               SkISize srcDimensions, SkIRect prevRect) {
+    const auto dimensions = dstInfo.dimensions();
+    if (dimensions != srcDimensions) {
+        SkRect src = SkRect::Make(srcDimensions);
+        SkRect dst = SkRect::Make(dimensions);
+        SkMatrix map = SkMatrix::MakeRectToRect(src, dst, SkMatrix::kCenter_ScaleToFit);
+        SkRect asRect = SkRect::Make(prevRect);
+        if (!map.mapRect(&asRect)) {
+            return false;
+        }
+        asRect.roundIn(&prevRect);
+        if (prevRect.isEmpty()) {
+            // Down-scaling shrank the empty portion to nothing,
+            // so nothing to zero.
+            return true;
+        }
     }
-    const auto info = dstInfo.makeWH(frameRect.width(), frameRect.height());
+
+    if (!prevRect.intersect(dstInfo.bounds())) {
+        SkCodecPrintf("rectangles do not intersect!");
+        SkASSERT(false);
+        return true;
+    }
+
+    const SkImageInfo info = dstInfo.makeWH(prevRect.width(), prevRect.height());
     const size_t bpp = dstInfo.bytesPerPixel();
-    const size_t offset = frameRect.x() * bpp + frameRect.y() * rowBytes;
-    auto* eraseDst = SkTAddOffset<void>(pixels, offset);
+    const size_t offset = prevRect.x() * bpp + prevRect.y() * rowBytes;
+    void* eraseDst = SkTAddOffset<void>(pixels, offset);
     SkSampler::Fill(info, eraseDst, rowBytes, 0, SkCodec::kNo_ZeroInitialized);
+    return true;
 }
 
 SkCodec::Result SkCodec::handleFrameIndex(const SkImageInfo& info, void* pixels, size_t rowBytes,
@@ -276,28 +297,9 @@ SkCodec::Result SkCodec::handleFrameIndex(const SkImageInfo& info, void* pixels,
                     // need to clear, since it must be covered by the desired frame.
                     if (options.fPriorFrame == requiredFrame) {
                         SkIRect prevRect = prevFrame->frameRect();
-                        if (info.dimensions() != fSrcInfo.dimensions()) {
-                            auto src = SkRect::Make(fSrcInfo.dimensions());
-                            auto dst = SkRect::Make(info.dimensions());
-                            SkMatrix map = SkMatrix::MakeRectToRect(src, dst,
-                                    SkMatrix::kCenter_ScaleToFit);
-                            SkRect asRect = SkRect::Make(prevRect);
-                            if (!map.mapRect(&asRect)) {
-                                return kInternalError;
-                            }
-                            asRect.roundIn(&prevRect);
-                            if (prevRect.isEmpty()) {
-                                // Down-scaling shrank the empty portion to nothing,
-                                // so nothing to zero.
-                                break;
-                            }
-                            if (!prevRect.intersect(SkIRect::MakeSize(info.dimensions()))) {
-                                SkCodecPrintf("rectangles do not intersect!");
-                                SkASSERT(false);
-                                break;
-                            }
+                        if (!zero_rect(info, pixels, rowBytes, fSrcInfo.dimensions(), prevRect)) {
+                            return kInternalError;
                         }
-                        zero_rect(info, pixels, rowBytes, prevRect);
                     }
                     break;
                 default:
@@ -314,7 +316,10 @@ SkCodec::Result SkCodec::handleFrameIndex(const SkImageInfo& info, void* pixels,
             const auto* prevFrame = frameHolder->getFrame(requiredFrame);
             const auto disposalMethod = prevFrame->getDisposalMethod();
             if (disposalMethod == SkCodecAnimation::DisposalMethod::kRestoreBGColor) {
-                zero_rect(info, pixels, rowBytes, prevFrame->frameRect());
+                auto prevRect = prevFrame->frameRect();
+                if (!zero_rect(info, pixels, rowBytes, fSrcInfo.dimensions(), prevRect)) {
+                    return kInternalError;
+                }
             }
         }
     }
diff --git a/tests/CodecAnimTest.cpp b/tests/CodecAnimTest.cpp
index a3e16c6aa5..4e069c17fb 100644
--- a/tests/CodecAnimTest.cpp
+++ b/tests/CodecAnimTest.cpp
@@ -422,9 +422,27 @@ DEF_TEST(AndroidCodec_animated, r) {
             options.fPriorFrame = i - 1;
             info = info.makeAlphaType(frameInfo.fAlphaType);
 
-            const auto result = codec->codec()->getPixels(info, bm.getPixels(), bm.rowBytes(),
-                                                          &options);
+            auto result = codec->codec()->getPixels(info, bm.getPixels(), bm.rowBytes(),
+                                                    &options);
             REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+
+            // Now compare to not using prior frame.
+            SkBitmap bm2;
+            bm2.allocPixels(info);
+
+            options.fPriorFrame = SkCodec::kNone;
+            result = codec->codec()->getPixels(info, bm2.getPixels(), bm2.rowBytes(),
+                                               &options);
+            REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+
+            for (int y = 0; y < info.height(); ++y) {
+                if (memcmp(bm.getAddr32(0, y), bm2.getAddr32(0, y), info.minRowBytes())) {
+                    ERRORF(r, "pixel mismatch for sample size %i, frame %i resulting in "
+                              "dimensions %i x %i line %i\n",
+                              sampleSize, i, info.width(), info.height(), y);
+                    break;
+                }
+            }
         }
     }
 }