Add subsetting to SkScaledCodec

src/codec/SkBmpCodec.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 "SkBmpCodec.h"
 #include "SkBmpMaskCodec.h"
 #include "SkBmpRLECodec.h"
@@ skipping 517 matching lines @@
         return codec;
     }
     return nullptr;
 }
 
 SkBmpCodec::SkBmpCodec(const SkImageInfo& info, SkStream* stream,
         uint16_t bitsPerPixel, SkCodec::SkScanlineOrder rowOrder)
     : INHERITED(info, stream)
     , fBitsPerPixel(bitsPerPixel)
     , fRowOrder(rowOrder)
+    , fSubsetLeft(0)
+    , fSubsetWidth(this->getInfo().width())
 {}
 
 bool SkBmpCodec::onRewind() {
-    return SkBmpCodec::ReadHeader(this->stream(), this->inIco(), nullptr);
+    if (!SkBmpCodec::ReadHeader(this->stream(), this->inIco(), nullptr)) {
+        return false;
+    }
+
+    fSubsetLeft = 0;
+    fSubsetWidth = this->getInfo().width();
+    return true;
 }
 
 int32_t SkBmpCodec::getDstRow(int32_t y, int32_t height) const {
     if (SkCodec::kTopDown_SkScanlineOrder == fRowOrder) {
         return y;
     }
     SkASSERT(SkCodec::kBottomUp_SkScanlineOrder == fRowOrder);
     return height - y - 1;
 }
 
 /*
  * Compute the number of colors in the color table
  */
 uint32_t SkBmpCodec::computeNumColors(uint32_t numColors) {
     // Zero is a default for maxColors
     // Also set numColors to maxColors when it is too large
     uint32_t maxColors = 1 << fBitsPerPixel;
     if (numColors == 0 || numColors >= maxColors) {
         return maxColors;
     }
     return numColors;
 }
 
 SkCodec::Result SkBmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
-        const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount) {
+        const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount,
+        int subsetLeft, int subsetWidth) {
     if (options.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
     }
     if (!conversion_possible(dstInfo, this->getInfo())) {
         SkCodecPrintf("Error: cannot convert input type to output type.\n");
         return kInvalidConversion;
     }
 
-    return prepareToDecode(dstInfo, options, inputColorPtr, inputColorCount);
+    this->fSubsetLeft = subsetLeft;
+    this->fSubsetWidth = subsetWidth;
+    return this->prepareToDecode(dstInfo, options, inputColorPtr, inputColorCount);
 }
 
 int SkBmpCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {
     // Create a new image info representing the portion of the image to decode
     SkImageInfo rowInfo = this->dstInfo().makeWH(this->dstInfo().width(), count);
 
     // Decode the requested rows
     return this->decodeRows(rowInfo, dst, rowBytes, this->options());
 }