Make SkAndroidCodec support ico

src/codec/SkBmpStandardCodec.cpp

Index: src/codec/SkBmpStandardCodec.cpp
diff --git a/src/codec/SkBmpStandardCodec.cpp b/src/codec/SkBmpStandardCodec.cpp
index fd4d6d18bc2d3df2ea6366554dc3bf56ec72700e..5bbdcd25e255cc3c237ea598a2789d2a71bc9f3f 100644
--- a/src/codec/SkBmpStandardCodec.cpp
+++ b/src/codec/SkBmpStandardCodec.cpp
@@ -27,6 +27,7 @@ SkBmpStandardCodec::SkBmpStandardCodec(const SkImageInfo& info, SkStream* stream
     , fSrcRowBytes(SkAlign4(compute_row_bytes(this->getInfo().width(), this->bitsPerPixel())))
     , fSrcBuffer(new uint8_t [fSrcRowBytes])
     , fInIco(inIco)
+    , fAndMaskRowBytes(fInIco ? SkAlign4(compute_row_bytes(this->getInfo().width(), 1)) : 0)
 {}
 
 /*
@@ -60,9 +61,6 @@ SkCodec::Result SkBmpStandardCodec::onGetPixels(const SkImageInfo& dstInfo,
         *rowsDecoded = rows;
         return kIncompleteInput;
     }
-    if (fInIco) {
-        return this->decodeIcoMask(dstInfo, dst, dstRowBytes);
-    }
     return kSuccess;
 }
 
@@ -227,9 +225,8 @@ SkCodec::Result SkBmpStandardCodec::prepareToDecode(const SkImageInfo& dstInfo,
 /*
  * Performs the bitmap decoding for standard input format
  */
-int SkBmpStandardCodec::decodeRows(const SkImageInfo& dstInfo,
-                                               void* dst, size_t dstRowBytes,
-                                               const Options& opts) {
+int SkBmpStandardCodec::decodeRows(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
+        const Options& opts) {
     // Iterate over rows of the image
     const int height = dstInfo.height();
     for (int y = 0; y < height; y++) {
@@ -246,29 +243,77 @@ int SkBmpStandardCodec::decodeRows(const SkImageInfo& dstInfo,
         fSwizzler->swizzle(dstRow, fSrcBuffer.get());
     }
 
-    // Finished decoding the entire image
+    if (fInIco) {
+        const int startScanline = this->currScanline();
+        if (startScanline < 0) {
+            // We are not performing a scanline decode.
+            // Just decode the entire ICO mask and return.
+            decodeIcoMask(this->stream(), dstInfo, dst, dstRowBytes);
+            return height;
+        }
+
+        // In order to perform a scanline ICO decode, we must be able
+        // to skip ahead in the stream in order to apply the AND mask
+        // to the requested scanlines.
+        // We will do this by taking advantage of the fact that
+        // SkIcoCodec always uses a SkMemoryStream as its underlying
+        // representation of the stream.
+        const void* memoryBase = this->stream()->getMemoryBase();
+        SkASSERT(nullptr != memoryBase);
+        SkASSERT(this->stream()->hasLength());
+        SkASSERT(this->stream()->hasPosition());
+
+        const size_t length = this->stream()->getLength();
+        const size_t currPosition = this->stream()->getPosition();
+
+        // Calculate how many bytes we must skip to reach the AND mask.
+        const int remainingScanlines = this->getInfo().height() - startScanline - height;
+        const size_t bytesToSkip = remainingScanlines * fSrcRowBytes +
+                startScanline * fAndMaskRowBytes;
+        const size_t subStreamStartPosition = currPosition + bytesToSkip;
+        if (subStreamStartPosition >= length) {
+            // FIXME: How can we indicate that this decode was actually incomplete?
+            return height;
+        }
+
+        // Create a subStream to pass to decodeIcoMask().  It is useful to encapsulate
+        // the memory base into a stream in order to safely handle incomplete images
+        // without reading out of bounds memory.
+        const void* subStreamMemoryBase = SkTAddOffset<const void>(memoryBase,
+                subStreamStartPosition);
+        const size_t subStreamLength = length - subStreamStartPosition;
+        // This call does not transfer ownership of the subStreamMemoryBase.
+        SkMemoryStream subStream(subStreamMemoryBase, subStreamLength, false);
+
+        // FIXME: If decodeIcoMask does not succeed, is there a way that we can
+        //        indicate the decode was incomplete?
+        decodeIcoMask(&subStream, dstInfo, dst, dstRowBytes);
+    }
+
     return height;
 }
 
-// TODO (msarett): This function will need to be modified in order to perform row by row decodes
-//                 when the Ico scanline decoder is implemented.
-SkCodec::Result SkBmpStandardCodec::decodeIcoMask(const SkImageInfo& dstInfo,
+void SkBmpStandardCodec::decodeIcoMask(SkStream* stream, const SkImageInfo& dstInfo,
         void* dst, size_t dstRowBytes) {
     // BMP in ICO have transparency, so this cannot be 565, and this mask
     // prevents us from using kIndex8. The below code depends on the output
     // being an SkPMColor.
     SkASSERT(dstInfo.colorType() == kN32_SkColorType);
 
-    // The AND mask is always 1 bit per pixel
-    const int width = this->getInfo().width();
-    const size_t rowBytes = SkAlign4(compute_row_bytes(width, 1));
+    // If we are sampling, make sure that we only mask the sampled pixels.
+    // We do not need to worry about sampling in the y-dimension because that
+    // should be handled by SkSampledCodec.
+    const int sampleX = fSwizzler->sampleX();
+    const int sampledWidth = get_scaled_dimension(this->getInfo().width(), sampleX);
+    const int srcStartX = get_start_coord(sampleX);
+
 
     SkPMColor* dstPtr = (SkPMColor*) dst;
     for (int y = 0; y < dstInfo.height(); y++) {
         // The srcBuffer will at least be large enough
-        if (stream()->read(fSrcBuffer.get(), rowBytes) != rowBytes) {
+        if (stream->read(fSrcBuffer.get(), fAndMaskRowBytes) != fAndMaskRowBytes) {
             SkCodecPrintf("Warning: incomplete AND mask for bmp-in-ico.\n");
-            return kIncompleteInput;
+            return;
         }
 
         int row = this->getDstRow(y, dstInfo.height());
@@ -276,17 +321,17 @@ SkCodec::Result SkBmpStandardCodec::decodeIcoMask(const SkImageInfo& dstInfo,
         SkPMColor* dstRow =
                 SkTAddOffset<SkPMColor>(dstPtr, row * dstRowBytes);
 
-        for (int x = 0; x < width; x++) {
+        int srcX = srcStartX;
+        for (int dstX = 0; dstX < sampledWidth; dstX++) {
             int quotient;
             int modulus;
-            SkTDivMod(x, 8, &quotient, &modulus);
+            SkTDivMod(srcX, 8, &quotient, &modulus);
             uint32_t shift = 7 - modulus;
-            uint32_t alphaBit =
-                    (fSrcBuffer.get()[quotient] >> shift) & 0x1;
-            dstRow[x] &= alphaBit - 1;
+            uint32_t alphaBit = (fSrcBuffer.get()[quotient] >> shift) & 0x1;
+            dstRow[dstX] &= alphaBit - 1;
+            srcX += sampleX;
         }
     }
-    return kSuccess;
 }
 
 uint32_t SkBmpStandardCodec::onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const {