Add support for encoding/decoding WebP images.

blimp/common/compositor/blimp_remote_image_serializer.cc

Index: blimp/common/compositor/blimp_remote_image_serializer.cc
diff --git a/blimp/common/compositor/blimp_remote_image_serializer.cc b/blimp/common/compositor/blimp_remote_image_serializer.cc
index 562c70d2f75401953f4eb022c6c48e42f0b07b23..1db3a6ef1a745a8f849e91552ad7c3eb5c0ff3b4 100644
--- a/blimp/common/compositor/blimp_remote_image_serializer.cc
+++ b/blimp/common/compositor/blimp_remote_image_serializer.cc
@@ -4,18 +4,145 @@
 
 #include "blimp/common/compositor/blimp_remote_image_serializer.h"
 
+#include <stddef.h>
+#include <vector>
+
+#include "third_party/libwebp/webp/encode.h"
+#include "third_party/skia/include/core/SkData.h"
 #include "third_party/skia/include/core/SkPixelSerializer.h"
 
+namespace {
+// TODO(nyquist): Make sure encoder does not serialize images more than once.
+// See crbug.com/548434.
+class WebPImageEncoder : public SkPixelSerializer {
+ public:
+  WebPImageEncoder() {}
+  ~WebPImageEncoder() override{};
+
+  bool onUseEncodedData(const void* data, size_t len) override {
+    const unsigned char* cast_data = static_cast<const unsigned char*>(data);
+    if (len < 10)

[urvang, 2016/02/10 23:54:42]

Don't you need first 14 bytes? (8 + 6)

[nyquist, 2016/02/11 05:19:23]

Done.

+      return false;
+    return !memcmp(cast_data, "RIFF", 4) && !memcmp(cast_data + 8, "WEBPVP", 6);
+  }
+
+  SkData* onEncode(const SkPixmap& pixmap) override {
+    auto pixel_chars = static_cast<const unsigned char*>(pixmap.addr());
+    WebPConfig config;
+    if (!WebPConfigInit(&config))
+      return nullptr;
+    WebPPicture picture;
+    if (!WebPPictureInit(&picture))
+      return nullptr;
+
+    if (!pixmap.width() || pixmap.width() > WEBP_MAX_DIMENSION)
+      return nullptr;
+    picture.width = pixmap.width();
+    if (!pixmap.height() || pixmap.height() > WEBP_MAX_DIMENSION)
+      return nullptr;
+    picture.height = pixmap.height();
+
+    const bool has_alpha = pixmap.alphaType() != kOpaque_SkAlphaType;
+    const bool premultiplied =
+        has_alpha && pixmap.alphaType() == kPremul_SkAlphaType;
+    if (premultiplied &&
+        !PlatformPremultipliedImportPicture(pixel_chars, &picture))
+      return nullptr;
+    if (!premultiplied && !ImportPictureRGBA<false>(pixel_chars, &picture))
+      return nullptr;
+
+    const int quality = 50;
+    std::vector<unsigned char> data;
+    picture.custom_ptr = &data;
+    picture.writer = &WebPImageEncoder::WriteOutput;
+    config.quality = quality;
+    config.method = 3;
+
+    bool success = WebPEncode(&config, &picture) != 0;

[urvang, 2016/02/10 23:54:42]

"!= 0" isn't really needed

[nyquist, 2016/02/11 05:19:23]

Done.

+    WebPPictureFree(&picture);
+    if (!success)
+      return nullptr;
+    return SkData::NewWithCopy(&data.front(), data.size());
+  }
+
+ private:
+  static int WriteOutput(const uint8_t* data,
+                         size_t size,
+                         const WebPPicture* const picture) {
+    std::vector<unsigned char>* dest =
+        static_cast<std::vector<unsigned char>*>(picture->custom_ptr);
+    dest->insert(dest->end(), data, data + size);
+    return 1;
+  }
+
+  typedef int (*WebPImporter)(WebPPicture* const,
+                              const uint8_t* const data,
+                              int row_stride);
+
+  bool RgbPictureImport(const unsigned char* pixels,

[urvang, 2016/02/10 23:54:42]

These parts were taken from an OLD version of
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...
I believe.

(1) That code was simplified a lot recently:
https://codereview.chromium.org/1319113002/diff/1/Source/platform/image-encod...

So, let me ask this question: in  your case also, don't you know for sure if you
expect pre-multiplied RGB or not? If you do, this import logic will become much
simpler here as well.

(2) That code has a missing part: it only imports RGB channels and alpha is
discarded. There's ongoing work to fix that: http://crrev.com/1302423004
Once that's done, you'll need the alpha channel imported here too.

[nyquist, 2016/02/11 05:19:23]

So, I tried to change the code so that it assumed that it was always
premultiplied. I'm not sure if I understood it correctly though.

Should I also check
has_alpha = pixmap.alphaType() != kOpaque_SkAlphaType;
and then use that to see if I need to  do the !premultiplied parts below?

Please advise.

+                        bool premultiplied,
+                        WebPImporter import_RGBA,
+                        WebPImporter import_RGB,
+                        WebPPicture* picture) {
+    if (premultiplied) {
+      return import_RGBA(picture, pixels,
+                         static_cast<int>(picture->width * 4)) != 0;
+    }
+
+    // Write the RGB pixels to an rgb data buffer, alpha premultiplied,
+    // then import the rgb data.
+
+    size_t pixelCount = picture->height * picture->width;
+    std::vector<unsigned char> rgb(pixelCount * 3);
+
+    for (unsigned char* data = rgb.data(); pixelCount-- > 0; pixels += 4) {
+      unsigned char alpha = pixels[3];
+      if (alpha != 255) {
+        *data++ = SkMulDiv255Round(pixels[0], alpha);
+        *data++ = SkMulDiv255Round(pixels[1], alpha);
+        *data++ = SkMulDiv255Round(pixels[2], alpha);
+      } else {
+        *data++ = pixels[0];
+        *data++ = pixels[1];
+        *data++ = pixels[2];
+      }
+    }
+
+    return import_RGB(picture, rgb.data(), picture->width * 3) != 0;
+  }
+
+  template <bool Premultiplied>
+  bool ImportPictureBGRA(const unsigned char* pixels, WebPPicture* picture) {
+    return RgbPictureImport(pixels, Premultiplied, &WebPPictureImportBGRA,
+                            &WebPPictureImportBGR, picture);
+  }
+
+  template <bool Premultiplied>
+  bool ImportPictureRGBA(const unsigned char* pixels, WebPPicture* picture) {
+    return RgbPictureImport(pixels, Premultiplied, &WebPPictureImportRGBA,
+                            &WebPPictureImportRGB, picture);
+  }
+
+  bool PlatformPremultipliedImportPicture(const unsigned char* pixels,
+                                          WebPPicture* picture) {
+    if (SK_B32_SHIFT)  // Android
+      return ImportPictureRGBA<true>(pixels, picture);
+
+    return ImportPictureBGRA<true>(pixels, picture);
+  }
+};
+
+}  // namespace
+
 namespace blimp {
 
-BlimpRemoteImageSerializer::BlimpRemoteImageSerializer() {}
+BlimpRemoteImageSerializer::BlimpRemoteImageSerializer()
+    : pixel_serializer_(make_scoped_ptr(new WebPImageEncoder)) {}
 
 BlimpRemoteImageSerializer::~BlimpRemoteImageSerializer() {}
 
 SkPixelSerializer* BlimpRemoteImageSerializer::GetPixelSerializer() {
-  // TODO(nyquist): Add an image encoder. Make sure it does not serialize images
-  // more than once. crbug.com/548434.
-  return nullptr;
+  return pixel_serializer_.get();
 }
 
 }  // namespace blimp