Add an option to create unpremultiplied bitmaps.

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index d967a69e84668c502ecf1bbd2c37dead68776447..8d32c68a1cc0cd763befcad6dd8724e170a52a75 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -80,7 +80,8 @@ private:
     SkPNGImageIndex* fImageIndex;
 
     bool onDecodeInit(SkStream* stream, png_structp *png_ptrp, png_infop *info_ptrp);
-    bool decodePalette(png_structp png_ptr, png_infop info_ptr, bool *hasAlphap,
+    bool decodePalette(png_structp png_ptr, png_infop info_ptr,
+                       SkBitmap::Config finalConfig, bool *hasAlphap,
                        bool *reallyHasAlphap, SkColorTable **colorTablep);
     bool getBitmapConfig(png_structp png_ptr, png_infop info_ptr,
                          SkBitmap::Config *config, bool *hasAlpha,
@@ -310,8 +311,12 @@ bool SkPNGImageDecoder::onDecode(SkStream* sk_stream, SkBitmap* decodedBitmap,
     }
 
     if (!reuseBitmap) {
+        bool premul = true;
+        if (SkBitmap::kARGB_8888_Config == config && this->getRequestUnpremultipliedColors()) {
+            premul = false;
+        }
         decodedBitmap->setConfig(config, sampler.scaledWidth(),
-                                 sampler.scaledHeight(), 0);
+                                 sampler.scaledHeight(), 0, premul);
     }
     if (SkImageDecoder::kDecodeBounds_Mode == mode) {
         return true;
@@ -326,7 +331,7 @@ bool SkPNGImageDecoder::onDecode(SkStream* sk_stream, SkBitmap* decodedBitmap,
     SkColorTable* colorTable = NULL;
 
     if (colorType == PNG_COLOR_TYPE_PALETTE) {
-        decodePalette(png_ptr, info_ptr, &hasAlpha, &reallyHasAlpha, &colorTable);
+        decodePalette(png_ptr, info_ptr, config, &hasAlpha, &reallyHasAlpha, &colorTable);
     }
 
     SkAutoUnref aur(colorTable);
@@ -549,9 +554,11 @@ bool SkPNGImageDecoder::getBitmapConfig(png_structp png_ptr, png_infop info_ptr,
     return this->chooseFromOneChoice(*configp, origWidth, origHeight);
 }
 
+typedef uint32_t (*PackColorProc)(U8CPU a, U8CPU r, U8CPU g, U8CPU b);
+
 bool SkPNGImageDecoder::decodePalette(png_structp png_ptr, png_infop info_ptr,
-                                      bool *hasAlphap, bool *reallyHasAlphap,
-                                      SkColorTable **colorTablep) {
+                                      SkBitmap::Config finalConfig, bool *hasAlphap,
+                                      bool *reallyHasAlphap, SkColorTable **colorTablep) {
     int numPalette;
     png_colorp palette;
     png_bytep trans;
@@ -587,9 +594,17 @@ bool SkPNGImageDecoder::decodePalette(png_structp png_ptr, png_infop info_ptr,
     int index = 0;
     int transLessThanFF = 0;
 
+    // Choose which function to use to create the color table. If the final destination's
+    // config is unpremultiplied, the color table will store unpremultiplied colors.
+    PackColorProc proc;
+    if (SkBitmap::kARGB_8888_Config == finalConfig && this->getRequestUnpremultipliedColors()) {
+        proc = &SkPackARGB32NoCheck;
+    } else {
+        proc = &SkPreMultiplyARGB;
+    }
     for (; index < numTrans; index++) {
         transLessThanFF |= (int)*trans - 0xFF;
-        *colorPtr++ = SkPreMultiplyARGB(*trans++, palette->red, palette->green, palette->blue);
+        *colorPtr++ = proc(*trans++, palette->red, palette->green, palette->blue);
         palette++;
     }
     reallyHasAlpha |= (transLessThanFF < 0);
@@ -679,7 +694,11 @@ bool SkPNGImageDecoder::onDecodeSubset(SkBitmap* bm, const SkIRect& region) {
     SkScaledBitmapSampler sampler(origWidth, rect.height(), sampleSize);
 
     SkBitmap decodedBitmap;
-    decodedBitmap.setConfig(config, sampler.scaledWidth(), sampler.scaledHeight(), 0);
+    bool premul = true;
+    if (SkBitmap::kARGB_8888_Config == config && this->getRequestUnpremultipliedColors()) {
+        premul = false;
+    }
+    decodedBitmap.setConfig(config, sampler.scaledWidth(), sampler.scaledHeight(), 0, premul);
 
     // from here down we are concerned with colortables and pixels
 
@@ -690,7 +709,7 @@ bool SkPNGImageDecoder::onDecodeSubset(SkBitmap* bm, const SkIRect& region) {
     SkColorTable* colorTable = NULL;
 
     if (colorType == PNG_COLOR_TYPE_PALETTE) {
-        decodePalette(png_ptr, info_ptr, &hasAlpha, &reallyHasAlpha, &colorTable);
+        decodePalette(png_ptr, info_ptr, config, &hasAlpha, &reallyHasAlpha, &colorTable);
     }
 
     SkAutoUnref aur(colorTable);