Allow drawing raster cache results whose device rect is one pixel larger than the cached image

RasterCacheResult::draw constructs the device target rectangle by
calling SkRect::roundOut, which rounds down the left/top coordinates
and rounds up the right/bottom coordinates.  The rounding can produce
a device rect whose width and/or height differs from the cache result
image's width/height by one pixel.

Author: jason-simmons

flow/raster_cache.cc

@@ -26,7 +26,9 @@ void RasterCacheResult::draw(SkCanvas& canvas, const SkPaint* paint) const {
   SkAutoCanvasRestore auto_restore(&canvas, true);
   SkIRect bounds =
       RasterCache::GetDeviceBounds(logical_rect_, canvas.getTotalMatrix());
-  FML_DCHECK(bounds.size() == image_->dimensions());
+  FML_DCHECK(
+      std::abs(bounds.size().width() - image_->dimensions().width()) <= 1 &&
+      std::abs(bounds.size().height() - image_->dimensions().height()) <= 1);
   canvas.resetMatrix();
   canvas.drawImage(image_, bounds.fLeft, bounds.fTop, paint);
 }

flow/raster_cache_unittests.cc

@@ -122,5 +122,37 @@ TEST(RasterCache, SweepsRemoveUnusedFrames) {
   ASSERT_FALSE(cache.Get(*picture, matrix).is_valid());
 }
 
+// Construct a cache result whose device target rectangle rounds out to be one
+// pixel wider than the cached image.  Verify that it can be drawn without
+// triggering any assertions.
+TEST(RasterCache, DeviceRectRoundOut) {
+  size_t threshold = 1;
+  flutter::RasterCache cache(threshold);
+
+  SkPictureRecorder recorder;
+  SkRect logical_rect = SkRect::MakeLTRB(28, 0, 354.56731, 310.288);
+  recorder.beginRecording(logical_rect);
+  SkPaint paint;
+  paint.setColor(SK_ColorRED);
+  recorder.getRecordingCanvas()->drawRect(logical_rect, paint);
+  sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
+
+  SkMatrix ctm = SkMatrix::MakeAll(1.3312, 0, 233, 0, 1.3312, 206, 0, 0, 1);
+
+  sk_sp<SkColorSpace> srgb = SkColorSpace::MakeSRGB();
+  ASSERT_FALSE(
+      cache.Prepare(NULL, picture.get(), ctm, srgb.get(), true, false));
+  ASSERT_FALSE(cache.Get(*picture, ctm).is_valid());
+  cache.SweepAfterFrame();
+  ASSERT_TRUE(cache.Prepare(NULL, picture.get(), ctm, srgb.get(), true, false));
+  ASSERT_TRUE(cache.Get(*picture, ctm).is_valid());
+
+  SkCanvas canvas(100, 100, nullptr);
+  canvas.setMatrix(ctm);
+  canvas.translate(248, 0);
+
+  cache.Get(*picture, ctm).draw(canvas);
+}
+
 }  // namespace testing
 }  // namespace flutter