Add BGRA as input format to SkColorSpaceXform

src/codec/SkWebpCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodecPriv.h"
 #include "SkColorSpaceXform.h"
 #include "SkWebpCodec.h"
@@ skipping 239 matching lines @@
     }
 
     SkISize dstDimensions = dstInfo.dimensions();
     if (bounds.size() != dstDimensions) {
         // Caller is requesting scaling.
         config.options.use_scaling = 1;
         config.options.scaled_width = dstDimensions.width();
         config.options.scaled_height = dstDimensions.height();
     }
 
-    // FIXME (msarett):
-    // Lossless webp is encoded as BGRA.  In that case, it would be more efficient to
-    // to decode BGRA and apply the color xform to a BGRA buffer.
-    config.output.colorspace = colorXform ? MODE_RGBA :
+    // Swizzling between RGBA and BGRA is zero cost in a color transform.  So when we have a
+    // color transform, we should decode to whatever is easiest for libwebp, and then let the
+    // color transform swizzle if necessary.
+    // Lossy webp is encoded as YUV (so RGBA and BGRA are the same cost).  Lossless webp is
+    // encoded as BGRA. This means decoding to BGRA is either faster or the same cost as RGBA.
+    config.output.colorspace = colorXform ? MODE_BGRA :
             webp_decode_mode(dstInfo.colorType(), dstInfo.alphaType() == kPremul_SkAlphaType);
     config.output.is_external_memory = 1;
 
     // We will decode the entire image and then perform the color transform.  libwebp
     // does not provide a row-by-row API.  This is a shame particularly in the F16 case,
     // where we need to allocate an extra image-sized buffer.
     SkAutoTMalloc<uint32_t> pixels;
     if (kRGBA_F16_SkColorType == dstInfo.colorType()) {
         pixels.reset(dstDimensions.width() * dstDimensions.height());
         config.output.u.RGBA.rgba = (uint8_t*) pixels.get();
@@ skipping 25 matching lines @@
         case VP8_STATUS_SUSPENDED:
             WebPIDecGetRGB(idec, rowsDecodedPtr, nullptr, nullptr, nullptr);
             rowsDecoded = *rowsDecodedPtr;
             result = kIncompleteInput;
             break;
         default:
             return kInvalidInput;
     }
 
     if (colorXform) {
-        SkColorSpaceXform::ColorFormat colorFormat = select_xform_format(dstInfo.colorType());
+        SkColorSpaceXform::ColorFormat dstColorFormat = select_xform_format(dstInfo.colorType());
         SkAlphaType xformAlphaType = select_xform_alpha(dstInfo.alphaType(),
                                                         this->getInfo().alphaType());
 
         uint32_t* src = (uint32_t*) config.output.u.RGBA.rgba;
         size_t srcRowBytes = config.output.u.RGBA.stride;
         for (int y = 0; y < rowsDecoded; y++) {
-            colorXform->apply(dst, src, dstInfo.width(), colorFormat, xformAlphaType);
+            colorXform->apply(dst, src, dstInfo.width(), dstColorFormat,
+                              SkColorSpaceXform::kBGRA_8888_ColorFormat, xformAlphaType);
             dst = SkTAddOffset<void>(dst, rowBytes);
             src = SkTAddOffset<uint32_t>(src, srcRowBytes);
         }
     }
 
     return result;
 }
 
 SkWebpCodec::SkWebpCodec(int width, int height, const SkEncodedInfo& info,
                          sk_sp<SkColorSpace> colorSpace, SkStream* stream, WebPDemuxer* demux,
                          sk_sp<SkData> data)
     : INHERITED(width, height, info, stream, std::move(colorSpace))
     , fDemux(demux)
     , fData(std::move(data))
 {}