[Impeller] Skip clip entity replay that cannot impact current clip. (#162113)

Fixes flutter/flutter#161262

Sometimes we end up with clip replay entities that have clip depth
values substantially below the current depth. I suspect this is due to
either mismatched save/restore or a bug in our code. Update: this isn't
a bug/bug but its definitely a bug. We can have multiple clips per save,
but the restore will remove at most one from the record/replay.


If a clip has a depth value that is less than the current clip depth, it
cannot by definition impact anything that draws after it.

Author: Jonah Williams

engine/src/flutter/impeller/display_list/aiks_dl_basic_unittests.cc

@@ -1592,5 +1592,33 @@ TEST_P(AiksTest, NoDimplesInRRectPath) {
   ASSERT_TRUE(OpenPlaygroundHere(callback));
 }
 
+TEST_P(AiksTest, BackdropFilterOverUnclosedClip) {
+  DisplayListBuilder builder;
+
+  builder.DrawPaint(DlPaint().setColor(DlColor::kWhite()));
+  builder.Save();
+  {
+    builder.ClipRect(DlRect::MakeLTRB(100, 100, 800, 800));
+
+    builder.Save();
+    {
+      builder.ClipRect(DlRect::MakeLTRB(600, 600, 800, 800));
+      builder.DrawPaint(DlPaint().setColor(DlColor::kRed()));
+      builder.DrawPaint(DlPaint().setColor(DlColor::kBlue().withAlphaF(0.5)));
+      builder.ClipRect(DlRect::MakeLTRB(700, 700, 750, 800));
+      builder.DrawPaint(DlPaint().setColor(DlColor::kRed().withAlphaF(0.5)));
+    }
+    builder.Restore();
+
+    auto image_filter = DlImageFilter::MakeBlur(10, 10, DlTileMode::kDecal);
+    builder.SaveLayer(std::nullopt, nullptr, image_filter.get());
+  }
+  builder.Restore();
+  builder.DrawCircle(SkPoint{100, 100}, 100,
+                     DlPaint().setColor(DlColor::kAqua()));
+
+  ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
+}
+
 }  // namespace testing
 }  // namespace impeller

engine/src/flutter/impeller/display_list/canvas.cc

@@ -1662,6 +1662,10 @@ std::shared_ptr<Texture> Canvas::FlipBackdrop(Point global_pass_position,
   // applied.
   auto& replay_entities = clip_coverage_stack_.GetReplayEntities();
   for (const auto& replay : replay_entities) {
+    if (replay.clip_depth <= current_depth_) {
+      continue;
+    }
+
     SetClipScissor(replay.clip_coverage, current_render_pass,
                    global_pass_position);
     if (!replay.clip_contents.Render(renderer_, current_render_pass,

engine/src/flutter/impeller/entity/entity_pass_clip_stack.cc

@@ -83,6 +83,9 @@ EntityPassClipStack::ClipStateResult EntityPassClipStack::RecordRestore(
   if (subpass_state.clip_coverage.back().coverage.has_value()) {
     FML_DCHECK(next_replay_index_ <=
                subpass_state.rendered_clip_entities.size());
+    // https://github.com/flutter/flutter/issues/162172
+    // This code is slightly wrong and should be popping more than one clip
+    // entry.
     if (!subpass_state.rendered_clip_entities.empty()) {
       subpass_state.rendered_clip_entities.pop_back();
 

engine/src/flutter/testing/impeller_golden_tests_output.txt

@@ -3,6 +3,9 @@ impeller_GoldenTests_ConicalGradient.png
 impeller_Play_AiksTest_AdvancedBlendColorFilterWithDestinationOpacity_Metal.png
 impeller_Play_AiksTest_AdvancedBlendColorFilterWithDestinationOpacity_OpenGLES.png
 impeller_Play_AiksTest_AdvancedBlendColorFilterWithDestinationOpacity_Vulkan.png
+impeller_Play_AiksTest_BackdropFilterOverUnclosedClip_Metal.png
+impeller_Play_AiksTest_BackdropFilterOverUnclosedClip_OpenGLES.png
+impeller_Play_AiksTest_BackdropFilterOverUnclosedClip_Vulkan.png
 impeller_Play_AiksTest_BackdropRestoreUsesCorrectCoverageForFirstRestoredClip_Metal.png
 impeller_Play_AiksTest_BackdropRestoreUsesCorrectCoverageForFirstRestoredClip_OpenGLES.png
 impeller_Play_AiksTest_BackdropRestoreUsesCorrectCoverageForFirstRestoredClip_Vulkan.png