[Impeller] make sure buffers are 4 aligned for foreground color blending

ci/licenses_golden/excluded_files

@@ -145,6 +145,7 @@
 ../../../flutter/impeller/display_list/skia_conversions_unittests.cc
 ../../../flutter/impeller/docs
 ../../../flutter/impeller/entity/contents/clip_contents_unittests.cc
+../../../flutter/impeller/entity/contents/filters/blend_filter_contents_unittests.cc
 ../../../flutter/impeller/entity/contents/filters/gaussian_blur_filter_contents_unittests.cc
 ../../../flutter/impeller/entity/contents/filters/inputs/filter_input_unittests.cc
 ../../../flutter/impeller/entity/contents/filters/matrix_filter_contents_unittests.cc

impeller/core/host_buffer.h

@@ -84,17 +84,19 @@ class HostBuffer {
   ///             host buffer.
   ///
   /// @param[in]  buffer        The buffer data.
+  /// @param[in]  alignment     Minimum alignment of the data being emplaced.
   ///
   /// @tparam     BufferType    The type of the buffer data.
   ///
   /// @return     The buffer view.
   ///
   template <class BufferType,
             class = std::enable_if_t<std::is_standard_layout_v<BufferType>>>
-  [[nodiscard]] BufferView Emplace(const BufferType& buffer) {
-    return Emplace(reinterpret_cast<const void*>(&buffer),  // buffer
-                   sizeof(BufferType),                      // size
-                   alignof(BufferType)                      // alignment
+  [[nodiscard]] BufferView Emplace(const BufferType& buffer,
+                                   size_t alignment = 0) {
+    return Emplace(reinterpret_cast<const void*>(&buffer),   // buffer
+                   sizeof(BufferType),                       // size
+                   std::max(alignment, alignof(BufferType))  // alignment
     );
   }
 

impeller/entity/BUILD.gn

@@ -239,6 +239,7 @@ impeller_component("entity_unittests") {
 
   sources = [
     "contents/clip_contents_unittests.cc",
+    "contents/filters/blend_filter_contents_unittests.cc",
     "contents/filters/gaussian_blur_filter_contents_unittests.cc",
     "contents/filters/inputs/filter_input_unittests.cc",
     "contents/filters/matrix_filter_contents_unittests.cc",

impeller/entity/contents/filters/blend_filter_contents.cc

@@ -867,7 +867,7 @@ std::optional<Entity> BlendFilterContents::CreateFramebufferAdvancedBlend(
     }
     auto blit_pass = cmd_buffer->CreateBlitPass();
     auto buffer_view = renderer.GetTransientsBuffer().Emplace(
-        foreground_color->Premultiply().ToR8G8B8A8());
+        foreground_color->Premultiply().ToR8G8B8A8(), /*alignment=*/4);
 
     blit_pass->AddCopy(std::move(buffer_view), foreground_texture);
     if (!blit_pass->EncodeCommands(

impeller/entity/contents/filters/blend_filter_contents_unittests.cc

@@ -0,0 +1,68 @@
+// 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/testing/testing.h"
+#include "gmock/gmock.h"
+#include "impeller/entity/contents/content_context.h"
+#include "impeller/entity/contents/filters/blend_filter_contents.h"
+#include "impeller/entity/entity_playground.h"
+
+namespace impeller {
+namespace testing {
+
+class BlendFilterContentsTest : public EntityPlayground {
+ public:
+  /// Create a texture that has been cleared to transparent black.
+  std::shared_ptr<Texture> MakeTexture(ISize size) {
+    std::shared_ptr<CommandBuffer> command_buffer =
+        GetContentContext()->GetContext()->CreateCommandBuffer();
+    if (!command_buffer) {
+      return nullptr;
+    }
+
+    auto render_target = GetContentContext()->MakeSubpass(
+        "Clear Subpass", size, command_buffer,
+        [](const ContentContext&, RenderPass&) { return true; });
+
+    if (!GetContentContext()
+             ->GetContext()
+             ->GetCommandQueue()
+             ->Submit(/*buffers=*/{command_buffer})
+             .ok()) {
+      return nullptr;
+    }
+
+    if (render_target.ok()) {
+      return render_target.value().GetRenderTargetTexture();
+    }
+    return nullptr;
+  }
+};
+INSTANTIATE_PLAYGROUND_SUITE(BlendFilterContentsTest);
+
+// https://github.com/flutter/flutter/issues/149216
+TEST_P(BlendFilterContentsTest, AdvancedBlendColorAlignsColorTo4) {
+  std::shared_ptr<Texture> texture = MakeTexture(ISize(100, 100));
+  BlendFilterContents filter_contents;
+  filter_contents.SetInputs({FilterInput::Make(texture)});
+  filter_contents.SetForegroundColor(Color(1.0, 0.0, 0.0, 1.0));
+  filter_contents.SetBlendMode(BlendMode::kColorDodge);
+
+  std::shared_ptr<ContentContext> renderer = GetContentContext();
+  // Add random byte to get the HostBuffer in a bad alignment.
+  uint8_t byte = 0xff;
+  BufferView buffer_view =
+      renderer->GetTransientsBuffer().Emplace(&byte, /*length=*/1, /*align=*/1);
+  EXPECT_EQ(buffer_view.range.offset, 4u);
+  EXPECT_EQ(buffer_view.range.length, 1u);
+  Entity entity;
+
+  std::optional<Entity> result = filter_contents.GetEntity(
+      *renderer, entity, /*coverage_hint=*/std::nullopt);
+
+  EXPECT_TRUE(result.has_value());
+}
+
+}  // namespace testing
+}  // namespace impeller