Fix bug in SkGifCodec / Switch SkImageDec tests to use Codec

src/codec/SkGifCodec.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 "SkColorPriv.h"
 #include "SkColorTable.h"
@@ skipping 400 matching lines @@
         colorCount = colorMap->ColorCount;
         // giflib guarantees these properties
         SkASSERT(colorCount == (unsigned) (1 << (colorMap->BitsPerPixel)));
         SkASSERT(colorCount <= 256);
         for (uint32_t i = 0; i < colorCount; i++) {
             colorPtr[i] = SkPackARGB32(0xFF, colorMap->Colors[i].Red,
                     colorMap->Colors[i].Green, colorMap->Colors[i].Blue);
         }
     }
 
-    // Gifs have the option to specify the color at a single index of the color
-    // table as transparent.  If the transparent index is greater than the
-    // colorCount, we know that there is no valid transparent color in the color
-    // table.  If there is not valid transparent index, we will try to use the
-    // backgroundIndex as the fill index.  If the backgroundIndex is also not
-    // valid, we will let fFillIndex default to 0 (it is set to zero in the
-    // constructor).  This behavior is not specified but matches
-    // SkImageDecoder_libgif.
-    uint32_t backgroundIndex = fGif->SBackGroundColor;
-    if (fTransIndex < colorCount) {
-        colorPtr[fTransIndex] = SK_ColorTRANSPARENT;
-        fFillIndex = fTransIndex;
-    } else if (backgroundIndex < colorCount) {
-        fFillIndex = backgroundIndex;
-    }
-
     // Fill in the color table for indices greater than color count.
     // This allows for predictable, safe behavior.
-    for (uint32_t i = colorCount; i < maxColors; i++) {
-        colorPtr[i] = colorPtr[fFillIndex];
+    if (colorCount > 0) {
+        // Gifs have the option to specify the color at a single index of the color
+        // table as transparent.  If the transparent index is greater than the
+        // colorCount, we know that there is no valid transparent color in the color
+        // table.  If there is not valid transparent index, we will try to use the
+        // backgroundIndex as the fill index.  If the backgroundIndex is also not
+        // valid, we will let fFillIndex default to 0 (it is set to zero in the
+        // constructor).  This behavior is not specified but matches
+        // SkImageDecoder_libgif.
+        uint32_t backgroundIndex = fGif->SBackGroundColor;
+        if (fTransIndex < colorCount) {
+            colorPtr[fTransIndex] = SK_ColorTRANSPARENT;
+            fFillIndex = fTransIndex;
+        } else if (backgroundIndex < colorCount) {
+            fFillIndex = backgroundIndex;
+        }
+
+        for (uint32_t i = colorCount; i < maxColors; i++) {
+            colorPtr[i] = colorPtr[fFillIndex];
+        }
+    } else {
+        sk_memset32(colorPtr, 0xFF000000, maxColors);
     }
 
     fColorTable.reset(new SkColorTable(colorPtr, maxColors));
     copy_color_table(dstInfo, this->fColorTable, inputColorPtr, inputColorCount);
 }
 
 SkCodec::Result SkGifCodec::prepareToDecode(const SkImageInfo& dstInfo, SkPMColor* inputColorPtr,
         int* inputColorCount, const Options& opts) {
     // Check for valid input parameters
     if (!conversion_possible(dstInfo, this->getInfo())) {
@@ skipping 144 matching lines @@
 int SkGifCodec::onOutputScanline(int inputScanline) const {
     if (fGif->Image.Interlace) {
         if (inputScanline < fFrameRect.top() || inputScanline >= fFrameRect.bottom()) {
             return inputScanline;
         }
         return get_output_row_interlaced(inputScanline - fFrameRect.top(), fFrameRect.height()) +
                 fFrameRect.top();
     }
     return inputScanline;
 }