[darwin] Update pixel format handling in FlutterTexture (#52326)

CVPixelBuffers from the application can have arbitrary pixel formats. However, current implementation doesn't support all pixel formats. To address this, add a comment to the FlutterTexture class to clarify which pixel formats are supported. Also, reject unsupported pixel formats so that the application can handle them properly.

Fixes [#147242](flutter/flutter#147242).

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: bc-lee

shell/platform/darwin/common/framework/Headers/FlutterTexture.h

@@ -19,7 +19,14 @@ FLUTTER_DARWIN_EXPORT
  * See also: https://github.com/flutter/plugins/tree/master/packages/camera
  */
 @protocol FlutterTexture <NSObject>
-/** Copy the contents of the texture into a `CVPixelBuffer`. */
+/**
+ * Copy the contents of the texture into a `CVPixelBuffer`.
+ *
+ * The type of the pixel buffer is one of the following:
+ * - `kCVPixelFormatType_32BGRA`
+ * - `kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange`
+ * - `kCVPixelFormatType_420YpCbCr8BiPlanarFullRange`
+ */
 - (CVPixelBufferRef _Nullable)copyPixelBuffer;
 
 /**

shell/platform/darwin/graphics/FlutterDarwinExternalTextureMetal.mm

@@ -133,8 +133,11 @@ - (void)onTextureUnregistered {
   if (_pixelFormat == kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange ||
       _pixelFormat == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange) {
     image = [self wrapNV12ExternalPixelBuffer:pixelBuffer context:context];
+  } else if (_pixelFormat == kCVPixelFormatType_32BGRA) {
+    image = [self wrapBGRAExternalPixelBuffer:pixelBuffer context:context];
   } else {
-    image = [self wrapRGBAExternalPixelBuffer:pixelBuffer context:context];
+    FML_LOG(ERROR) << "Unsupported pixel format: " << _pixelFormat;
+    return nullptr;
   }
 
   if (!image) {
@@ -235,7 +238,7 @@ - (void)onTextureUnregistered {
   return flutter::DlImage::Make(skImage);
 }
 
-- (sk_sp<flutter::DlImage>)wrapRGBAExternalPixelBuffer:(CVPixelBufferRef)pixelBuffer
+- (sk_sp<flutter::DlImage>)wrapBGRAExternalPixelBuffer:(CVPixelBufferRef)pixelBuffer
                                                context:(flutter::Texture::PaintContext&)context {
   SkISize textureSize =
       SkISize::Make(CVPixelBufferGetWidth(pixelBuffer), CVPixelBufferGetHeight(pixelBuffer));

shell/platform/darwin/macos/framework/Source/FlutterEmbedderExternalTextureTest.mm

@@ -288,4 +288,50 @@ - (CVPixelBufferRef)pixelBuffer {
   gpuSurface->makeImageSnapshot();
 }
 
+TEST_F(FlutterEmbedderExternalTextureTest, TestPopulateUnsupportedExternalTexture) {
+  // Constants.
+  const size_t width = 100;
+  const size_t height = 100;
+  const int64_t texture_id = 1;
+
+  // Set up the surface.
+  FlutterDarwinContextMetalSkia* darwinContextMetal =
+      [[FlutterDarwinContextMetalSkia alloc] initWithDefaultMTLDevice];
+  SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
+  GrDirectContext* grContext = darwinContextMetal.mainContext.get();
+  sk_sp<SkSurface> gpuSurface(SkSurfaces::RenderTarget(grContext, skgpu::Budgeted::kNo, info));
+
+  // Create a texture.
+  TestExternalTexture* testExternalTexture =
+      [[TestExternalTexture alloc] initWidth:width
+                                      height:height
+                             pixelFormatType:kCVPixelFormatType_420YpCbCr8PlanarFullRange];
+  FlutterExternalTexture* textureHolder =
+      [[FlutterExternalTexture alloc] initWithFlutterTexture:testExternalTexture
+                                          darwinMetalContext:darwinContextMetal];
+
+  // Callback to resolve the texture.
+  EmbedderExternalTextureMetal::ExternalTextureCallback callback = [&](int64_t texture_id, size_t w,
+                                                                       size_t h) {
+    EXPECT_TRUE(w == width);
+    EXPECT_TRUE(h == height);
+
+    auto texture = std::make_unique<FlutterMetalExternalTexture>();
+    EXPECT_FALSE([textureHolder populateTexture:texture.get()]);
+    return nullptr;
+  };
+
+  // Render the texture.
+  std::unique_ptr<flutter::Texture> texture =
+      std::make_unique<EmbedderExternalTextureMetal>(texture_id, callback);
+  SkRect bounds = SkRect::MakeWH(info.width(), info.height());
+  DlImageSampling sampling = DlImageSampling::kNearestNeighbor;
+  DlSkCanvasAdapter canvas(gpuSurface->getCanvas());
+  flutter::Texture::PaintContext context{
+      .canvas = &canvas,
+      .gr_context = grContext,
+  };
+  texture->Paint(context, bounds, /*freeze=*/false, sampling);
+}
+
 }  // namespace flutter::testing

shell/platform/darwin/macos/framework/Source/FlutterExternalTexture.mm

@@ -43,8 +43,11 @@ - (BOOL)populateTexture:(FlutterMetalExternalTexture*)textureOut {
   if (pixel_format == kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange ||
       pixel_format == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange) {
     return [self populateTextureFromYUVAPixelBuffer:pixelBuffer textureOut:textureOut];
-  } else {
+  } else if (pixel_format == kCVPixelFormatType_32BGRA) {
     return [self populateTextureFromRGBAPixelBuffer:pixelBuffer textureOut:textureOut];
+  } else {
+    NSLog(@"Unsupported pixel format: %d", pixel_format);
+    return NO;
   }
 }