HTML <canvas>: add WEBP lossless encoding support

third_party/WebKit/Source/platform/image-encoders/skia/WEBPImageEncoder.cpp

Index: third_party/WebKit/Source/platform/image-encoders/skia/WEBPImageEncoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-encoders/skia/WEBPImageEncoder.cpp b/third_party/WebKit/Source/platform/image-encoders/skia/WEBPImageEncoder.cpp
index 47711ba6320d5f987c06529ca63780ef472eae30..a6ce021b0f1d4aa5ca5d33eadaea417d3e7c3ba0 100644
--- a/third_party/WebKit/Source/platform/image-encoders/skia/WEBPImageEncoder.cpp
+++ b/third_party/WebKit/Source/platform/image-encoders/skia/WEBPImageEncoder.cpp
@@ -34,8 +34,6 @@
 #include "platform/graphics/ImageBuffer.h"
 #include "webp/encode.h"
 
-typedef int (*WebPImporter)(WebPPicture* const, const uint8_t* const data, int rowStride);
-
 namespace blink {
 
 static int writeOutput(const uint8_t* data, size_t size, const WebPPicture* const picture)
@@ -44,32 +42,6 @@ static int writeOutput(const uint8_t* data, size_t size, const WebPPicture* cons
     return 1;
 }
 
-static bool rgbPictureImport(const unsigned char* pixels, WebPImporter importRGB, WebPPicture* picture)
-{
-    // Write the RGB pixels to an rgb data buffer, alpha premultiplied, then import the rgb data.
-
-    size_t pixelCount = picture->height * picture->width;
-
-    OwnPtr<unsigned char[]> rgb = adoptArrayPtr(new unsigned char[pixelCount * 3]);
-    if (!rgb.get())
-        return false;
-
-    for (unsigned char* data = rgb.get(); 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 importRGB(picture, rgb.get(), picture->width * 3);
-}
-
 static bool encodePixels(const IntSize& imageSize, const unsigned char* pixels, int quality, Vector<unsigned char>* output)
 {
     if (imageSize.width() <= 0 || imageSize.width() > WEBP_MAX_DIMENSION)
@@ -87,13 +59,23 @@ static bool encodePixels(const IntSize& imageSize, const unsigned char* pixels,
     picture.width = imageSize.width();
     picture.height = imageSize.height();
 
-    if (!rgbPictureImport(pixels, &WebPPictureImportRGB, &picture))
+    bool useLosslessEncoding = (quality >= 100);
+    if (useLosslessEncoding)
+        picture.use_argb = 1;
+    if (!WebPPictureImportRGBA(&picture, pixels, picture.width * 4))
         return false;
 
     picture.custom_ptr = output;
     picture.writer = &writeOutput;
-    config.quality = quality;
-    config.method = 3;
+
+    if (useLosslessEncoding) {
+        config.lossless = 1;
+        config.quality = 75;

[Noel Gordon, 2016/05/04 01:15:58]

Note urvang@: the config.{quality,method} values used here are the ones you
suggested from a previous patch.  I assume they still look good.

+        config.method = 0;
+    } else {
+        config.quality = quality;
+        config.method = 3;
+    }
 
     bool success = WebPEncode(&config, &picture);
     WebPPictureFree(&picture);