[Impeller] Return an empty contents in Paint::CreateContents if a runtime effect sampler is invalid (#165165)

Callers of Paint::CreateContents expect that the result is not null.

See flutter/flutter#165119

Author: jason-simmons

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

@@ -108,5 +108,33 @@ TEST_P(AiksTest, CanRenderRuntimeEffectFilter) {
   ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
 }
 
+TEST_P(AiksTest, RuntimeEffectWithInvalidSamplerDoesNotCrash) {
+  ScopedValidationDisable disable_validation;
+
+  // Create a sampler that is not usable as an input to the runtime effect.
+  std::vector<flutter::DlColor> colors = {flutter::DlColor::kBlue(),
+                                          flutter::DlColor::kRed()};
+  const float stops[2] = {0.0, 1.0};
+  auto linear = flutter::DlColorSource::MakeLinear({0.0, 0.0}, {300.0, 300.0},
+                                                   2, colors.data(), stops,
+                                                   flutter::DlTileMode::kClamp);
+  std::vector<std::shared_ptr<DlColorSource>> sampler_inputs = {
+      linear,
+  };
+
+  auto uniform_data = std::make_shared<std::vector<uint8_t>>();
+  uniform_data->resize(sizeof(Vector2));
+
+  DlPaint paint;
+  paint.setColorSource(
+      MakeRuntimeEffect(this, "runtime_stage_filter_example.frag.iplr",
+                        uniform_data, sampler_inputs));
+
+  DisplayListBuilder builder;
+  builder.DrawPaint(paint);
+
+  ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
+}
+
 }  // namespace testing
 }  // namespace impeller

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

@@ -218,11 +218,17 @@ std::shared_ptr<ColorSourceContents> Paint::CreateContents() const {
 
       for (auto& sampler : samplers) {
         if (sampler == nullptr) {
-          return nullptr;
+          VALIDATION_LOG << "Runtime effect sampler is null";
+          auto contents = std::make_shared<SolidColorContents>();
+          contents->SetColor(Color::BlackTransparent());
+          return contents;
         }
         auto* image = sampler->asImage();
         if (!sampler->asImage()) {
-          return nullptr;
+          VALIDATION_LOG << "Runtime effect sampler is not an image";
+          auto contents = std::make_shared<SolidColorContents>();
+          contents->SetColor(Color::BlackTransparent());
+          return contents;
         }
         FML_DCHECK(image->image()->impeller_texture());
         texture_inputs.push_back({

engine/src/flutter/testing/impeller_golden_tests_output.txt

@@ -877,6 +877,9 @@ impeller_Play_AiksTest_ReleasesTextureOnTeardown_Vulkan.png
 impeller_Play_AiksTest_RotateColorFilteredPath_Metal.png
 impeller_Play_AiksTest_RotateColorFilteredPath_OpenGLES.png
 impeller_Play_AiksTest_RotateColorFilteredPath_Vulkan.png
+impeller_Play_AiksTest_RuntimeEffectWithInvalidSamplerDoesNotCrash_Metal.png
+impeller_Play_AiksTest_RuntimeEffectWithInvalidSamplerDoesNotCrash_OpenGLES.png
+impeller_Play_AiksTest_RuntimeEffectWithInvalidSamplerDoesNotCrash_Vulkan.png
 impeller_Play_AiksTest_SaveLayerDrawsBehindSubsequentEntities_Metal.png
 impeller_Play_AiksTest_SaveLayerDrawsBehindSubsequentEntities_OpenGLES.png
 impeller_Play_AiksTest_SaveLayerDrawsBehindSubsequentEntities_Vulkan.png