Revert of Add color xform support to SkWebpCodec

src/codec/SkPngCodec.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 "SkBitmap.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 76 matching lines @@
         fPng_ptr = nullptr;
         fInfo_ptr = nullptr;
     }
 
 private:
     png_structp     fPng_ptr;
     png_infop       fInfo_ptr;
 };
 #define AutoCleanPng(...) SK_REQUIRE_LOCAL_VAR(AutoCleanPng)
 
+static inline SkAlphaType xform_alpha_type(SkAlphaType dstAlphaType, SkAlphaType srcAlphaType) {
+    return (kOpaque_SkAlphaType == srcAlphaType) ? kOpaque_SkAlphaType : dstAlphaType;
+}
+
 // Note: SkColorTable claims to store SkPMColors, which is not necessarily the case here.
 bool SkPngCodec::createColorTable(const SkImageInfo& dstInfo, int* ctableCount) {
 
     int numColors;
     png_color* palette;
     if (!png_get_PLTE(fPng_ptr, fInfo_ptr, &palette, &numColors)) {
         return false;
     }
 
     // Contents depend on tableColorType and our choice of if/when to premultiply:
@@ skipping 37 matching lines @@
             SkOpts::RGB_to_BGR1(colorTable + numColorsWithAlpha, palette,
                     numColors - numColorsWithAlpha);
         }
     }
 
     // If we are not decoding to F16, we can color xform now and store the results
     // in the color table.
     if (fColorXform && kRGBA_F16_SkColorType != dstInfo.colorType()) {
         SkColorType xformColorType = is_rgba(dstInfo.colorType()) ?
                 kRGBA_8888_SkColorType : kBGRA_8888_SkColorType;
-        SkAlphaType xformAlphaType = select_alpha_xform(dstInfo.alphaType(),
-                                                        this->getInfo().alphaType());
+        SkAlphaType xformAlphaType = xform_alpha_type(dstInfo.alphaType(),
+                                                      this->getInfo().alphaType());
         fColorXform->apply(colorTable, colorTable, numColors, xformColorType, xformAlphaType);
     }
 
     // Pad the color table with the last color in the table (or black) in the case that
     // invalid pixel indices exceed the number of colors in the table.
     const int maxColors = 1 << fBitDepth;
     if (numColors < maxColors) {
         SkPMColor lastColor = numColors > 0 ? colorTable[numColors - 1] : SK_ColorBLACK;
         sk_memset32(colorTable + numColors, lastColor, maxColors - numColors);
     }
@@ skipping 270 matching lines @@
     override {
         SkASSERT(0 == startRow);
 
         // Assume that an error in libpng indicates an incomplete input.
         int y = 0;
         if (setjmp(png_jmpbuf((png_struct*)fPng_ptr))) {
             SkCodecPrintf("Failed to read row.\n");
             return y;
         }
 
-        SkAlphaType xformAlphaType = select_alpha_xform(dstInfo.alphaType(),
-                                                        this->getInfo().alphaType());
+        SkAlphaType xformAlphaType = xform_alpha_type(dstInfo.alphaType(),
+                                                      this->getInfo().alphaType());
         int width = fSwizzler ? fSwizzler->swizzleWidth() : dstInfo.width();
 
         for (; y < count; y++) {
             png_read_row(fPng_ptr, fSwizzlerSrcRow, nullptr);
             this->applyXformRow(dst, fSwizzlerSrcRow, dstInfo.colorType(), xformAlphaType, width);
             dst = SkTAddOffset<void>(dst, rowBytes);
         }
 
         return y;
     }
@@ skipping 64 matching lines @@
             for (int y = 0; y < count; y++) {
                 png_read_row(fPng_ptr, srcRow, nullptr);
                 srcRow += fSrcRowBytes;
             }
             // Discard rows that we don't need.
             for (int y = 0; y < this->getInfo().height() - startRow - count; y++) {
                 png_read_row(fPng_ptr, fSwizzlerSrcRow, nullptr);
             }
         }
 
-        SkAlphaType xformAlphaType = select_alpha_xform(dstInfo.alphaType(),
-                                                        this->getInfo().alphaType());
+        SkAlphaType xformAlphaType = xform_alpha_type(dstInfo.alphaType(),
+                                                      this->getInfo().alphaType());
         int width = fSwizzler ? fSwizzler->swizzleWidth() : dstInfo.width();
         srcRow = storage.get();
         for (int y = 0; y < count; y++) {
             this->applyXformRow(dst, srcRow, dstInfo.colorType(), xformAlphaType, width);
             srcRow = SkTAddOffset<uint8_t>(srcRow, fSrcRowBytes);
             dst = SkTAddOffset<void>(dst, rowBytes);
         }
 
         return count;
     }
@@ skipping 397 matching lines @@
     SkCodec* outCodec;
     if (read_header(stream, chunkReader, &outCodec, nullptr, nullptr)) {
         // Codec has taken ownership of the stream.
         SkASSERT(outCodec);
         streamDeleter.release();
         return outCodec;
     }
 
     return nullptr;
 }