[Impeller] fix incorrect origins for mesh gradient computation. (#54762)

Fixes flutter/flutter#153964

Changing the origin of the rect used to render a shader could break shaders that expect to render at particular coordinates based on the input vertices. The snapshot functionality correctly handles translating a texture, so the translation was never necessary to begin with.

impeller/aiks/canvas.cc

@@ -970,21 +970,21 @@ void Canvas::DrawVertices(const std::shared_ptr<VerticesGeometry>& vertices,
         // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
         vertices->GetTextureCoordinateCoverge().value_or(cvg.value());
   }
-  Rect translated_coverage = Rect::MakeSize(src_coverage.GetSize());
   src_contents = src_paint.CreateContentsForGeometry(
-      Geometry::MakeRect(translated_coverage));
+      Geometry::MakeRect(Rect::Round(src_coverage)));
 
   auto contents = std::make_shared<VerticesSimpleBlendContents>();
   contents->SetBlendMode(blend_mode);
   contents->SetAlpha(paint.color.alpha);
   contents->SetGeometry(vertices);
   contents->SetLazyTextureCoverage(src_coverage);
   contents->SetLazyTexture(
-      [src_contents, translated_coverage](const ContentContext& renderer) {
+      [src_contents, src_coverage](const ContentContext& renderer) {
         // Applying the src coverage as the coverage limit prevents the 1px
         // coverage pad from adding a border that is picked up by developer
         // specified UVs.
-        return src_contents->RenderToSnapshot(renderer, {}, translated_coverage)
+        return src_contents
+            ->RenderToSnapshot(renderer, {}, Rect::Round(src_coverage))
             ->texture;
       });
   entity.SetContents(paint.WithFilters(std::move(contents)));

impeller/display_list/aiks_dl_vertices_unittests.cc

@@ -379,7 +379,7 @@ TEST_P(AiksTest, DrawVerticesWithInvalidIndices) {
 }
 
 // All four vertices should form a solid red rectangle with no gaps.
-// The blur rectangle drawn under them should not be visible.
+// The blue rectangle drawn under them should not be visible.
 TEST_P(AiksTest, DrawVerticesTextureCoordinatesWithFragmentShader) {
   std::vector<SkPoint> positions_lt = {
       SkPoint::Make(0, 0),    //
@@ -468,5 +468,54 @@ TEST_P(AiksTest, DrawVerticesTextureCoordinatesWithFragmentShader) {
   ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
 }
 
+// The vertices should form a solid red rectangle with no gaps.
+// The blue rectangle drawn under them should not be visible.
+TEST_P(AiksTest,
+       DrawVerticesTextureCoordinatesWithFragmentShaderNonZeroOrigin) {
+  std::vector<SkPoint> positions_lt = {
+      SkPoint::Make(200, 200),  //
+      SkPoint::Make(250, 200),  //
+      SkPoint::Make(200, 250),  //
+      SkPoint::Make(250, 250),  //
+  };
+
+  auto vertices = flutter::DlVertices::Make(
+      flutter::DlVertexMode::kTriangleStrip, positions_lt.size(),
+      positions_lt.data(),
+      /*texture_coordinates=*/positions_lt.data(), /*colors=*/nullptr,
+      /*index_count=*/0,
+      /*indices=*/nullptr);
+
+  flutter::DisplayListBuilder builder;
+  flutter::DlPaint paint;
+  flutter::DlPaint rect_paint;
+  rect_paint.setColor(DlColor::kBlue());
+
+  auto runtime_stages =
+      OpenAssetAsRuntimeStage("runtime_stage_position.frag.iplr");
+
+  auto runtime_stage =
+      runtime_stages[PlaygroundBackendToRuntimeStageBackend(GetBackend())];
+  ASSERT_TRUE(runtime_stage);
+
+  auto runtime_effect = DlRuntimeEffect::MakeImpeller(runtime_stage);
+  auto rect_data = std::vector<Rect>{Rect::MakeLTRB(200, 200, 250, 250)};
+
+  auto uniform_data = std::make_shared<std::vector<uint8_t>>();
+  uniform_data->resize(rect_data.size() * sizeof(Rect));
+  memcpy(uniform_data->data(), rect_data.data(), uniform_data->size());
+
+  auto color_source = flutter::DlColorSource::MakeRuntimeEffect(
+      runtime_effect, {}, uniform_data);
+
+  paint.setColorSource(color_source);
+
+  builder.Scale(GetContentScale().x, GetContentScale().y);
+  builder.DrawRect(SkRect::MakeLTRB(200, 200, 250, 250), rect_paint);
+  builder.DrawVertices(vertices, flutter::DlBlendMode::kSrcOver, paint);
+
+  ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
+}
+
 }  // namespace testing
 }  // namespace impeller

impeller/entity/contents/vertices_contents.cc

@@ -5,14 +5,14 @@
 #include "vertices_contents.h"
 
 #include "fml/logging.h"
+#include "impeller/base/validation.h"
 #include "impeller/core/formats.h"
 #include "impeller/entity/contents/content_context.h"
 #include "impeller/entity/contents/contents.h"
 #include "impeller/entity/contents/filters/blend_filter_contents.h"
 #include "impeller/entity/geometry/geometry.h"
 #include "impeller/entity/geometry/vertices_geometry.h"
 #include "impeller/geometry/color.h"
-#include "impeller/geometry/size.h"
 #include "impeller/renderer/render_pass.h"
 
 namespace impeller {
@@ -113,6 +113,10 @@ bool VerticesSimpleBlendContents::Render(const ContentContext& renderer,
   } else {
     texture = renderer.GetEmptyTexture();
   }
+  if (!texture) {
+    VALIDATION_LOG << "Missing texture for VerticesSimpleBlendContents";
+    return false;
+  }
 
   auto dst_sampler_descriptor = descriptor_;
   dst_sampler_descriptor.width_address_mode =

impeller/fixtures/BUILD.gn

@@ -91,6 +91,7 @@ impellerc("runtime_stages") {
     "ink_sparkle.frag",
     "runtime_stage_example.frag",
     "runtime_stage_simple.frag",
+    "runtime_stage_position.frag",
     "gradient.frag",
     "uniforms_and_sampler_1.frag",
     "uniforms_and_sampler_2.frag",

impeller/fixtures/runtime_stage_position.frag

@@ -0,0 +1,19 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <flutter/runtime_effect.glsl>
+
+uniform vec4 ltrb;
+
+out vec4 frag_color;
+
+// Output solid red if frag position is within LTRB rectangle.
+void main() {
+  if (FlutterFragCoord().x >= ltrb.x && FlutterFragCoord().x <= ltrb.z &&
+      FlutterFragCoord().y >= ltrb.y && FlutterFragCoord().y <= ltrb.w) {
+    frag_color = vec4(1.0, 0.0, 0.0, 1.0);
+  } else {
+    frag_color = vec4(0.0);
+  }
+}

testing/impeller_golden_tests_output.txt

@@ -608,6 +608,9 @@ impeller_Play_AiksTest_DrawVerticesSolidColorTrianglesWithIndices_Vulkan.png
 impeller_Play_AiksTest_DrawVerticesSolidColorTrianglesWithoutIndices_Metal.png
 impeller_Play_AiksTest_DrawVerticesSolidColorTrianglesWithoutIndices_OpenGLES.png
 impeller_Play_AiksTest_DrawVerticesSolidColorTrianglesWithoutIndices_Vulkan.png
+impeller_Play_AiksTest_DrawVerticesTextureCoordinatesWithFragmentShaderNonZeroOrigin_Metal.png
+impeller_Play_AiksTest_DrawVerticesTextureCoordinatesWithFragmentShaderNonZeroOrigin_OpenGLES.png
+impeller_Play_AiksTest_DrawVerticesTextureCoordinatesWithFragmentShaderNonZeroOrigin_Vulkan.png
 impeller_Play_AiksTest_DrawVerticesTextureCoordinatesWithFragmentShader_Metal.png
 impeller_Play_AiksTest_DrawVerticesTextureCoordinatesWithFragmentShader_OpenGLES.png
 impeller_Play_AiksTest_DrawVerticesTextureCoordinatesWithFragmentShader_Vulkan.png