Composite imaged onto canvas by direct blitting or alphablending

Author: bdero

lib/ui/painting/image_generator_apng.cc

@@ -6,7 +6,9 @@
 #include <cstddef>
 
 #include "third_party/libpng/png.h"
+#include "third_party/skia/include/codec/SkCodecAnimation.h"
 #include "third_party/skia/src/codec/SkPngCodec.h"
+#include "third_party/skia/src/core/SkRasterPipeline.h"
 #include "third_party/zlib/zlib.h"  // For crc32
 
 namespace flutter {
@@ -64,33 +66,46 @@ bool APNGImageGenerator::GetPixels(const SkImageInfo& info,
   FML_DCHECK(images_.size() > 0);
   unsigned int image_index = first_frame_index_ + frame_index;
 
-  // If the frame doesn't exist in the APNG chunk stream, fall back to the
-  // mandatory "default" image (always at index 0).
+  // 1. Demux the frame from the APNG stream.
+
   if (!DemuxToImageIndex(image_index)) {
     FML_DLOG(ERROR) << "Couldn't demux image at index " << image_index
                     << " (frame index: " << frame_index
                     << ") from APNG stream.";
+    return RenderDefaultImage(info, pixels, row_bytes);
+  }
+
+  // 2. Decode the frame.
+
+  APNGImage& frame = images_[image_index];
+  auto frame_info = frame.codec->getInfo();
+  auto frame_row_bytes = frame_info.bytesPerPixel() * frame_info.width();
 
-    SkCodec::Result result =
-        images_[0].codec->getPixels(info, pixels, row_bytes);
+  if (frame.pixels.empty()) {
+    frame.pixels.resize(frame_row_bytes * frame_info.height());
+    SkCodec::Result result = frame.codec->getPixels(
+        frame.codec->getInfo(), frame.pixels.data(), frame_row_bytes);
     if (result != SkCodec::kSuccess) {
-      FML_DLOG(ERROR) << "Failed to decode the APNG's default/fallback image. "
-                         "SkCodec::Result: "
-                      << result;
-      return false;
+      FML_DLOG(ERROR) << "Failed to decode image at index " << image_index
+                      << " (frame index: " << frame_index
+                      << ") of APNG. SkCodec::Result: " << result;
+      return RenderDefaultImage(info, pixels, row_bytes);
     }
-    return true;
   }
 
-  APNGImage& frame = images_[image_index];
+  // 3. Composite the frame onto the canvas.
 
-  SkCodec::Result result = frame.codec->getPixels(info, pixels, row_bytes);
-  if (result != SkCodec::kSuccess) {
-    FML_DLOG(ERROR) << "Failed to decode image at index " << image_index
-                    << " (frame index: " << frame_index
-                    << ") of APNG. SkCodec::Result: " << result;
-    return false;
+  for (int i = 0; i < frame_info.height(); i++) {
+    void* source = frame.pixels.data() + i * frame_row_bytes;
+    void* destination = (uint8_t*)pixels +
+                        frame.x_offset * frame_info.bytesPerPixel() +
+                        (i + frame.y_offset) * row_bytes;
+
+    BlendLine(info.colorType(), destination, frame_info.colorType(), source,
+              info.alphaType(), frame.frame_info->blend_mode,
+              frame_info.width());
   }
+
   return true;
 }
 
@@ -412,11 +427,6 @@ bool APNGImageGenerator::DemuxNextImageInternal() {
     return false;
   }
 
-  // TODO(bdero): Cache rendered frames and discard their codecs. There is no
-  //   circumstance where frames can ever change on repeat (according to the
-  //   APNG spec).
-  // TODO(bdero): Alpha blend with the `prior_frame` if the blending mode is
-  //   appropriate.
   std::optional<APNGImage> image;
   void* data_p = (void*)data_.get()->data();
   std::tie(image, next_chunk_p_) =
@@ -425,11 +435,21 @@ bool APNGImageGenerator::DemuxNextImageInternal() {
     return false;
   }
 
+  if (!images_.empty() && images_.back().frame_info->disposal_method ==
+                              SkCodecAnimation::DisposalMethod::kKeep) {
+    image->frame_info->required_frame = images_.size() - 1;
+  }
+
   // Calling SkCodec::getInfo at least once prior to decoding is mandatory.
   SkImageInfo info = image.value().codec->getInfo();
   FML_DCHECK(info.colorInfo() == image_info_.colorInfo());
 
   images_.push_back(std::move(image.value()));
+
+  auto default_info = images_[0].codec->getInfo();
+  if (info.colorType() != default_info.colorType()) {
+    return false;
+  }
   return true;
 }
 
@@ -479,4 +499,49 @@ uint32_t APNGImageGenerator::ChunkHeader::ComputeChunkCrc32() {
   return crc;
 }
 
+void APNGImageGenerator::BlendLine(SkColorType dest_colortype,
+                                   void* dest,
+                                   SkColorType source_colortype,
+                                   const void* source,
+                                   SkAlphaType dest_alphatype,
+                                   SkCodecAnimation::Blend blend_mode,
+                                   int width) {
+  SkRasterPipeline_MemoryCtx dst_ctx = {(void*)dest, 0},
+                             src_ctx = {(void*)source, 0};
+
+  SkRasterPipeline_<256> p;
+
+  p.append_load_dst(dest_colortype, &dst_ctx);
+  if (kUnpremul_SkAlphaType == dest_alphatype) {
+    p.append(SkRasterPipeline::premul_dst);
+  }
+
+  p.append_load(source_colortype, &src_ctx);
+  p.append(SkRasterPipeline::premul);
+
+  if (blend_mode == SkCodecAnimation::Blend::kSrcOver) {
+    p.append(SkRasterPipeline::srcover);
+  }
+
+  if (kUnpremul_SkAlphaType == dest_alphatype) {
+    p.append(SkRasterPipeline::unpremul);
+  }
+  p.append_store(dest_colortype, &dst_ctx);
+
+  p.run(0, 0, width, 1);
+}
+
+bool APNGImageGenerator::RenderDefaultImage(const SkImageInfo& info,
+                                            void* pixels,
+                                            size_t row_bytes) {
+  SkCodec::Result result = images_[0].codec->getPixels(info, pixels, row_bytes);
+  if (result != SkCodec::kSuccess) {
+    FML_DLOG(ERROR) << "Failed to decode the APNG's default/fallback image. "
+                       "SkCodec::Result: "
+                    << result;
+    return false;
+  }
+  return true;
+}
+
 }  // namespace flutter

lib/ui/painting/image_generator_apng.h

@@ -112,8 +112,8 @@ class APNGImageGenerator : public ImageGenerator {
   struct APNGImage {
     std::unique_ptr<SkCodec> codec;
 
-    // The composited image is populated
-    std::shared_ptr<SkImage> composited_image;
+    // The rendered frame pixels.
+    std::vector<uint8_t> pixels;
 
     // Absense of frame info is possible on the "default" image.
     std::optional<ImageGenerator::FrameInfo> frame_info;
@@ -185,6 +185,18 @@ class APNGImageGenerator : public ImageGenerator {
 
   bool DemuxToImageIndex(unsigned int image_index);
 
+  static void BlendLine(SkColorType dest_colortype,
+                        void* dest,
+                        SkColorType source_colortype,
+                        const void* source,
+                        SkAlphaType dest_alphatype,
+                        SkCodecAnimation::Blend blend_mode,
+                        int width);
+
+  bool RenderDefaultImage(const SkImageInfo& info,
+                          void* pixels,
+                          size_t row_bytes);
+
   FML_DISALLOW_COPY_ASSIGN_AND_MOVE(APNGImageGenerator);
   sk_sp<SkData> data_;
   SkImageInfo image_info_;