[composite-bgcolor-animation] Return empty result when PaintWorkletIn…

…put not found The root cause of the problem is that there is an early exit in the DiscardableImageMap::GatherDiscardableImages(), happening when the paint rect for the op is empty. This makes sense because there is nothing to draw. Note that this is different than the empty element case. In fact, we already have "background-color-animation-zero-size-element.html" under css-backgrounds/animations/ and there is no problem with that. The bug happens when the element is not empty, but its intersection with the SkCanvas that it draws into is empty. Please see the notes in this doc for more details: https://docs.google.com/document/d/1Da9d7ai5xt4nPX7NDZnqaaTSoFitRSeYxw1qxGjtdeQ/edit The |PaintWorkletImageProvider::records_| contains the records for all the discardable images that can draw. Meaning that the ones that early exits won't be included in the |records_|. But, when the PaintWorkletImageProvider::GetPaintRecordResult() is called, the input parameter |PaintWorkletInput| would contain all possible PaintWorkletInput that is passed from Blink to CC, which obviously contains the ones that cannot draw. As a result, these PaintWorkletInputs won't exists in the |records_|. We handle these cases by returning an empty record because there is nothing to draw (like empty container cases). Bug: 1216210 Change-Id: I9630aa4b55fd1322f641f42b05c20aab8c7234c7 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2954479 Reviewed-by: Philip Rogers <pdr@chromium.org> Reviewed-by: Robert Flack <flackr@chromium.org> Commit-Queue: Xida Chen <xidachen@chromium.org> Cr-Commit-Position: refs/heads/master@{#894050}
marcosholgado · Jun 19, 2021 · d43f760 · d43f760
1 parent 0090f94
commit d43f760
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Showing 2 changed files with 22 additions and 3 deletions.
diff --git a/cc/raster/paint_worklet_image_provider.cc b/cc/raster/paint_worklet_image_provider.cc
@@ -23,10 +23,13 @@ PaintWorkletImageProvider& PaintWorkletImageProvider::operator=(
 
 ImageProvider::ScopedResult PaintWorkletImageProvider::GetPaintRecordResult(
     scoped_refptr<PaintWorkletInput> input) {
-  // The |records_| contains all known PaintWorkletInputs, whether they are
-  // painted or not, so |input| should always exist in it.
   auto it = records_.find(input);
-  DCHECK(it != records_.end());
+  // In the DiscardableImageMap::GatherDiscardableImages(), a DrawImageRect can
+  // early exit the for loop if its paint rect is empty. In that case, the
+  // |records_| will not contain that PaintWorkletInput, and we should return
+  // an empty result.
+  if (it == records_.end())
+    return ImageProvider::ScopedResult();
   return ImageProvider::ScopedResult(it->second.second);
 }
 

diff --git a/...pt/css/css-backgrounds/animations/background-color-animation-non-empty-no-draw-crash.html b/...pt/css/css-backgrounds/animations/background-color-animation-non-empty-no-draw-crash.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/css-backgrounds-3/#background-color">
+<style>
+@keyframes bgcolor {
+
+  0% { background: blue; }
+  100% { background: none; }
+}
+.target {
+  animation: bgcolor 50ms;
+  opacity: 0.9;
+  height: 0.4px;
+  margin: 21.6px;
+}
+</style>
+<div class="target"></div>