Create an SkAndroidCodec API separate from SkCodec

src/codec/SkScaledCodec.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 "SkCodec.h"
 #include "SkCodecPriv.h"
 #include "SkScaledCodec.h"
-#include "SkStream.h"
-#include "SkWebpCodec.h"
-
-
-SkCodec* SkScaledCodec::NewFromStream(SkStream* stream) {
-    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(stream));
-    if (nullptr == codec) {
-        return nullptr;
-    }
-
-    switch (codec->getEncodedFormat()) {
-        case kWEBP_SkEncodedFormat:
-            // Webp codec supports scaling and subsetting natively
-            return codec.detach();
-        case kPNG_SkEncodedFormat:
-        case kJPEG_SkEncodedFormat:
-            // wrap in new SkScaledCodec
-            return new SkScaledCodec(codec.detach());
-        default:
-            // FIXME: SkScaledCodec is temporarily disabled for other formats
-            // while focusing on the formats that are supported by
-            // BitmapRegionDecoder.
-            return nullptr;
-    }
-}
-
-SkCodec* SkScaledCodec::NewFromData(SkData* data) {
-    if (!data) {
-        return nullptr;
-    }
-    return NewFromStream(new SkMemoryStream(data));
-}
-
-SkScaledCodec::SkScaledCodec(SkCodec* codec)
-    : INHERITED(codec->getInfo(), nullptr)
+
+SkSampledCodec::SkSampledCodec(SkCodec* codec)
+    : INHERITED(codec->getInfo())
     , fCodec(codec)
 {}
 
-SkScaledCodec::~SkScaledCodec() {}
-
-bool SkScaledCodec::onRewind() {
-    return fCodec->onRewind();
-}
-
-static SkISize best_scaled_dimensions(const SkISize& origDims, const SkISize& nativeDims,
-                                      const SkISize& scaledCodecDims, float desiredScale) {
-    if (nativeDims == scaledCodecDims) {
-        // does not matter which to return if equal. Return here to skip below calculations
-        return nativeDims;
-    }
-    float idealWidth = origDims.width() * desiredScale;
-    float idealHeight = origDims.height() * desiredScale;
-
-    // calculate difference between native dimensions and ideal dimensions
-    float nativeWDiff = SkTAbs(idealWidth - nativeDims.width());
-    float nativeHDiff = SkTAbs(idealHeight - nativeDims.height());
-    float nativeDiff = nativeWDiff + nativeHDiff;
-
-    // Native scaling is preferred to sampling.  If we can scale natively to
-    // within one of the ideal value, we should choose to scale natively.
-    if (nativeWDiff < 1.0f && nativeHDiff < 1.0f) {
-        return nativeDims;
-    }
-
-    // calculate difference between scaledCodec dimensions and ideal dimensions
-    float scaledCodecWDiff = SkTAbs(idealWidth - scaledCodecDims.width());
-    float scaledCodecHDiff = SkTAbs(idealHeight - scaledCodecDims.height());
-    float scaledCodecDiff = scaledCodecWDiff + scaledCodecHDiff;
-
-    // return dimensions closest to ideal dimensions.
-    // If the differences are equal, return nativeDims, as native scaling is more efficient.
-    return nativeDiff > scaledCodecDiff ? scaledCodecDims : nativeDims;
-}
-
-/*
- * Return a valid set of output dimensions for this decoder, given an input scale
- */
-SkISize SkScaledCodec::onGetScaledDimensions(float desiredScale) const {
-    SkISize nativeDimensions = fCodec->getScaledDimensions(desiredScale);
-    // support scaling down by integer numbers. Ex: 1/2, 1/3, 1/4 ...
-    SkISize scaledCodecDimensions;
-    if (desiredScale > 0.5f) {
-        // sampleSize = 1
-        scaledCodecDimensions = fCodec->getInfo().dimensions();
-    }
-    // sampleSize determines the step size between samples
-    // Ex: sampleSize = 2, sample every second pixel in x and y directions
-    int sampleSize = int ((1.0f / desiredScale) + 0.5f);
-
-    int scaledWidth = get_scaled_dimension(this->getInfo().width(), sampleSize);
-    int scaledHeight = get_scaled_dimension(this->getInfo().height(), sampleSize);
-
-    // Return the calculated output dimensions for the given scale
-    scaledCodecDimensions = SkISize::Make(scaledWidth, scaledHeight);
-
-    return best_scaled_dimensions(this->getInfo().dimensions(), nativeDimensions,
-                                  scaledCodecDimensions, desiredScale);
-}
-
-// check if scaling to dstInfo size from srcInfo size using sampleSize is possible
-static bool scaling_supported(const SkISize& dstDim, const SkISize& srcDim,
-                              int* sampleX, int* sampleY) {
-    SkScaledCodec::ComputeSampleSize(dstDim, srcDim, sampleX, sampleY);
-    const int dstWidth = dstDim.width();
-    const int dstHeight = dstDim.height();
-    const int srcWidth = srcDim.width();
-    const int srcHeight = srcDim.height();
-     // only support down sampling, not up sampling
-    if (dstWidth > srcWidth || dstHeight  > srcHeight) {
-        return false;
-    }
-    // check that srcWidth is scaled down by an integer value
-    if (get_scaled_dimension(srcWidth, *sampleX) != dstWidth) {
-        return false;
-    }
-    // check that src height is scaled down by an integer value
-    if (get_scaled_dimension(srcHeight, *sampleY) != dstHeight) {
-        return false;
-    }
-    // sampleX and sampleY should be equal unless the original sampleSize requested was larger
-    // than srcWidth or srcHeight. If so, the result of this is dstWidth or dstHeight = 1.
-    // This functionality allows for tall thin images to still be scaled down by scaling factors.
-    if (*sampleX != *sampleY){
-        if (1 != dstWidth && 1 != dstHeight) {
-            return false;
-        }
-    }
-    return true;
-}
-
-bool SkScaledCodec::onDimensionsSupported(const SkISize& dim) {
-    // Check with fCodec first. No need to call the non-virtual version, which
-    // just checks if it matches the original, since a match means this method
-    // will not be called.
-    if (fCodec->onDimensionsSupported(dim)) {
-        return true;
-    }
-
-    // FIXME: These variables are unused, but are needed by scaling_supported.
-    // This class could also cache these values, and avoid calling this in
-    // onGetPixels (since getPixels already calls it).
-    int sampleX;
-    int sampleY;
-    return scaling_supported(dim, this->getInfo().dimensions(), &sampleX, &sampleY);
-}
-
-// calculates sampleSize in x and y direction
-void SkScaledCodec::ComputeSampleSize(const SkISize& dstDim, const SkISize& srcDim,
-                                      int* sampleXPtr, int* sampleYPtr) {
-    int srcWidth = srcDim.width();
-    int dstWidth = dstDim.width();
-    int srcHeight = srcDim.height();
-    int dstHeight = dstDim.height();
-
-    int sampleX = srcWidth / dstWidth;
-    int sampleY = srcHeight / dstHeight;
-
-    // only support down sampling, not up sampling
-    SkASSERT(dstWidth <= srcWidth);
-    SkASSERT(dstHeight <= srcHeight);
-
-    // sampleX and sampleY should be equal unless the original sampleSize requested was
-    // larger than srcWidth or srcHeight.
-    // If so, the result of this is dstWidth or dstHeight = 1. This functionality
-    // allows for tall thin images to still be scaled down by scaling factors.
-
-    if (sampleX != sampleY){
-        if (1 != dstWidth && 1 != dstHeight) {
-
-            // rounding during onGetScaledDimensions can cause different sampleSizes
-            // Ex: srcWidth = 79, srcHeight = 20, sampleSize = 10
-            // dstWidth = 7, dstHeight = 2, sampleX = 79/7 = 11, sampleY = 20/2 = 10
-            // correct for this rounding by comparing width to sampleY and height to sampleX
-
-            if (get_scaled_dimension(srcWidth, sampleY) == dstWidth) {
-                sampleX = sampleY;
-            } else if (get_scaled_dimension(srcHeight, sampleX) == dstHeight) {
-                sampleY = sampleX;
-            }
-        }
-    }
-
-    if (sampleXPtr) {
-        *sampleXPtr = sampleX;
-    }
-    if (sampleYPtr) {
-        *sampleYPtr = sampleY;
-    }
-}
-
-// TODO: Implement subsetting in onGetPixels which works when and when not sampling 
-
-SkCodec::Result SkScaledCodec::onGetPixels(const SkImageInfo& requestedInfo, void* dst,
-                                           size_t rowBytes, const Options& options,
-                                           SkPMColor ctable[], int* ctableCount,
-                                           int* rowsDecoded) {
-
+static bool is_in_range(int coord, int offset, int length) {

[scroggo, 2015/10/16 21:13:55]

I still need to look over this file in more detail...

+    return coord >= offset && coord < offset + length;
+}
+
+SkISize SkSampledCodec::onGetSampledDimensions(int sampleSize) const {
+    // Fast path for when we are not scaling.
+    if (1 == sampleSize) {
+        return fCodec->getInfo().dimensions();
+    }
+
+    const int width = fCodec->getInfo().width();
+    const int height = fCodec->getInfo().height();
+
+    // Check if the codec can provide the scaling natively.
+    float scale = get_scale_from_sample_size(sampleSize);
+    SkSize idealSize = SkSize::Make(scale * (float) width, scale * (float) height);
+    SkISize nativeSize = fCodec->getScaledDimensions(scale);
+    float widthDiff = SkTAbs(((float) nativeSize.width()) - idealSize.width());
+    float heightDiff = SkTAbs(((float) nativeSize.height()) - idealSize.height());
+    if (widthDiff < 1.0f && heightDiff < 1.0f) {
+        return nativeSize;
+    }
+
+    // Provide the scaling by sampling.
+    return SkISize::Make(get_scaled_dimension(width, sampleSize),
+            get_scaled_dimension(height, sampleSize));
+}
+
+SkISize SkSampledCodec::onGetSampledSubsetDimensions(int sampleSize, const SkIRect& subset) const {

[scroggo, 2015/10/19 20:03:20]

Interesting - this function is no longer virtual (this code is just inside
getSampledSubsetDimensions directly). Probably makes sense since we only have
two implementations and they're happy with the same answer. It might be a little
weird though, since it makes an assumption about what its subclass can do.

[msarett, 2015/10/19 21:39:21]

Yeah I agree that it makes sense but is a little weird.

My other concern was that it's not as maintainable.  If/when we decide to
add/change a subclass, I'll get to add the virtual back in :).

+    // This call is less expensive than onGetSampledDimensions() because, regardless
+    // of the scaling method, we are free to choose how many of the pixels that we
+    // want to clip.
+    // Alternatively, we could call onGetSampledDimensions(), calculate the scale
+    // as a float and do our best to apply an identical scale here.  But I'm not
+    // sure that there is any added benefit to that approach.
+
+    // We should, however, be sure that if the subset specifies the entire image,
+    // we will perform a full image decode.
+    if (fCodec->getInfo().dimensions() == subset.size()) {
+        return onGetSampledDimensions(sampleSize);
+    }
+
+    return SkISize::Make(get_scaled_dimension(subset.width(), sampleSize),
+                get_scaled_dimension(subset.height(), sampleSize));
+}
+
+SkCodec::Result SkSampledCodec::onGetAndroidPixels(const SkImageInfo& info, void* pixels,
+        size_t rowBytes, AndroidOptions& options) {
+    // Create an Options struct for the codec.
+    SkCodec::Options codecOptions;
+    codecOptions.fZeroInitialized = options.fZeroInitialized;
+
+    SkIRect* subset = options.fSubset;
+    if (!subset || subset->size() == fCodec->getInfo().dimensions()) {
+        // Try to use the native codec to perform the decode.
+        SkCodec::Result result = fCodec->getPixels(info, pixels, rowBytes, &codecOptions,
+                options.fColorPtr, options.fColorCount);
+
+        if (SkCodec::kInvalidScale != result) {
+            return result;
+        }
+
+        // If the native codec does not support the requested scale, scale by sampling.
+        return sampledDecode(info, pixels, rowBytes, options);
+    }
+
+    // We are performing a subset decode.
+    // First attempt to use the native codec.  The native codec needs to know the scaled size
+    // of the image and the subset.
+    int sampleSize = options.fSampleSize;
+    // FIXME: We already make this same function call in getAndroidPixels().
+    SkISize scaledSize = this->onGetSampledDimensions(sampleSize);
+    int scaledSubsetX = subset->x() / sampleSize;
+    int scaledSubsetY = subset->y() / sampleSize;
+    int scaledSubsetWidth = info.width();
+    int scaledSubsetHeight = info.height();
+
+    // The scanline decoder only needs to be aware of scaledSubsetX and scaledSubestWidth.
+    // We will handling subsetting in the y-dimension by skipping scanlines.
+    SkIRect scanlineSubset = SkIRect::MakeXYWH(scaledSubsetX, 0, scaledSubsetWidth,
+            scaledSize.height());
+    codecOptions.fSubset = &scanlineSubset;
+    SkCodec::Result result = fCodec->startScanlineDecode(info.makeWH(scaledSize.width(),
+            scaledSize.height()), &codecOptions, options.fColorPtr, options.fColorCount);
+    switch (result) {
+        case SkCodec::kSuccess:
+            break;
+        case SkCodec::kInvalidScale:
+            // If the native codec does not support the requested scale, scale by sampling.
+            return sampledDecode(info, pixels, rowBytes, options);
+        default:
+            return result;
+    }
+
+    switch (fCodec->getScanlineOrder()) {
+        case SkCodec::kTopDown_SkScanlineOrder:
+        case SkCodec::kNone_SkScanlineOrder: {
+            if (!fCodec->skipScanlines(scaledSubsetY)) {
+                fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                        scaledSubsetHeight, 0);
+                return SkCodec::kIncompleteInput;
+            }
+
+            int decodedLines = fCodec->getScanlines(pixels, scaledSubsetHeight, rowBytes);
+            if (decodedLines != scaledSubsetHeight) {
+                return SkCodec::kIncompleteInput;
+            }
+            return SkCodec::kSuccess;
+        }
+        case SkCodec::kBottomUp_SkScanlineOrder:
+        case SkCodec::kOutOfOrder_SkScanlineOrder: {
+            for (int y = 0; y < scaledSize.height(); y++) {
+                int dstY = fCodec->nextScanline();
+                if (is_in_range(dstY, scaledSubsetY, scaledSubsetHeight)) {
+                    void* pixelsPtr = SkTAddOffset<void>(pixels, rowBytes * (dstY - scaledSubsetY));
+                    if (1 != fCodec->getScanlines(pixelsPtr, 1, rowBytes)) {
+                        // FIXME: Fill incomplete images skbug.com/4428
+                        return SkCodec::kIncompleteInput;
+                    }
+                } else {
+                    if (!fCodec->skipScanlines(1)) {
+                        // FIXME: Fill incomplete images skbug.com/4428
+                        return SkCodec::kIncompleteInput;
+                    }
+                }
+            }
+            return SkCodec::kSuccess;
+        }
+        default:
+            SkASSERT(false);
+            return SkCodec::kUnimplemented;
+    }
+}
+
+
+SkCodec::Result SkSampledCodec::sampledDecode(const SkImageInfo& info, void* pixels,
+        size_t rowBytes, AndroidOptions& options) {
+    // Create options struct for the codec.
+    SkCodec::Options sampledOptions;
+    sampledOptions.fZeroInitialized = options.fZeroInitialized;
+
+    // Check if there is a subset.
+    SkIRect subset;
+    int subsetY = 0;
+    int subsetWidth = fCodec->getInfo().width();
+    int subsetHeight = fCodec->getInfo().height();
     if (options.fSubset) {
-        // Subsets are not supported.
-        return kUnimplemented;
-    }
-
-    if (fCodec->dimensionsSupported(requestedInfo.dimensions())) {
-        // Make sure that the parent class does not fill on an incomplete decode, since
-        // fCodec will take care of filling the uninitialized lines.
-        *rowsDecoded = requestedInfo.height();
-        return fCodec->getPixels(requestedInfo, dst, rowBytes, &options, ctable, ctableCount);
-    }
-
-    // scaling requested
-    int sampleX;
-    int sampleY;
-    if (!scaling_supported(requestedInfo.dimensions(), fCodec->getInfo().dimensions(),
-                           &sampleX, &sampleY)) {
-        // onDimensionsSupported would have returned false, meaning we should never reach here.
-        SkASSERT(false);
-        return kInvalidScale;
-    }
-
-    // set first sample pixel in y direction
-    const int Y0 = get_start_coord(sampleY);
-
-    const int dstHeight = requestedInfo.height();
-    const int srcWidth = fCodec->getInfo().width();
-    const int srcHeight = fCodec->getInfo().height();
-
-    const SkImageInfo info = requestedInfo.makeWH(srcWidth, srcHeight);
-
-    Result result = fCodec->startScanlineDecode(info, &options, ctable, ctableCount);
-
-    if (kSuccess != result) {
+        // We will need to know about subsetting in the y-dimension in order to use the
+        // scanline decoder.
+        SkIRect* subsetPtr = options.fSubset;
+        subsetY = subsetPtr->y();
+        subsetWidth = subsetPtr->width();
+        subsetHeight = subsetPtr->height();
+
+        // The scanline decoder only needs to be aware of subsetting in the x-dimension.
+        subset.setXYWH(subsetPtr->x(), 0, subsetWidth, fCodec->getInfo().height());
+        sampledOptions.fSubset = &subset;
+    }
+
+    // Start the scanline decode.
+    SkCodec::Result result = fCodec->startScanlineDecode(
+            info.makeWH(fCodec->getInfo().width(), fCodec->getInfo().height()), &sampledOptions,
+            options.fColorPtr, options.fColorCount);
+    if (SkCodec::kSuccess != result) {
+        // If scaling is not supported, we should have caught the error
+        // in getAndroidPixels().
+        SkASSERT(SkCodec::kInvalidScale != result);
         return result;
     }
 
     SkSampler* sampler = fCodec->getSampler(true);
     if (!sampler) {
-        return kUnimplemented;
-    }
-
-    if (sampler->setSampleX(sampleX) != requestedInfo.width()) {
-        return kInvalidScale;
-    }
-
+        return SkCodec::kUnimplemented;
+    }
+
+    // Since we guarantee that output dimensions are always at least one (even if the sampleSize
+    // is greater than a given dimension), the input sampleSize is not always the sampleSize that
+    // we use in practice.
+    int sampleX = subsetWidth / info.width();
+    int sampleY = subsetHeight / info.height();
+    if (sampler->setSampleX(sampleX) != info.width()) {
+        SkASSERT(false);
+        return SkCodec::kInvalidScale;
+    }
+
+    int y0 = get_start_coord(sampleY);
+    int dstHeight = info.height();
     switch(fCodec->getScanlineOrder()) {
         case SkCodec::kTopDown_SkScanlineOrder: {
-            if (!fCodec->skipScanlines(Y0)) {
-                *rowsDecoded = 0;
-                return kIncompleteInput;
-            }
+            if (!fCodec->skipScanlines(y0 + subsetY)) {
+                fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                        dstHeight, 0);
+                return SkCodec::kIncompleteInput;
+            }
+            void* pixelPtr = pixels;
             for (int y = 0; y < dstHeight; y++) {
-                if (1 != fCodec->getScanlines(dst, 1, rowBytes)) {
-                    // The failed call to getScanlines() will take care of
-                    // filling the failed row, so we indicate that we have
-                    // decoded (y + 1) rows.
-                    *rowsDecoded = y + 1;
-                    return kIncompleteInput;
-                }
-                if (y < dstHeight - 1) {
-                    if (!fCodec->skipScanlines(sampleY - 1)) {
-                        *rowsDecoded = y + 1;
-                        return kIncompleteInput;
-                    }
-                }
-                dst = SkTAddOffset<void>(dst, rowBytes);
-            }
-            return kSuccess;
+                if (1 != fCodec->getScanlines(pixelPtr, 1, rowBytes)) {
+                    fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                            dstHeight, y + 1);
+                    return SkCodec::kIncompleteInput;
+                }
+                int linesToSkip = SkTMin(sampleY - 1, dstHeight - y - 1);
+                if (!fCodec->skipScanlines(linesToSkip)) {
+                    fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                            dstHeight, y + 1);
+                    return SkCodec::kIncompleteInput;
+                }
+                pixelPtr = SkTAddOffset<void>(pixelPtr, rowBytes);
+            }
+            return SkCodec::kSuccess;
         }
         case SkCodec::kBottomUp_SkScanlineOrder:
         case SkCodec::kOutOfOrder_SkScanlineOrder: {
-            Result result = kSuccess;
+            SkCodec::Result result = SkCodec::kSuccess;
             int y;
-            for (y = 0; y < srcHeight; y++) {
+            for (y = 0; y < fCodec->getInfo().height(); y++) {
                 int srcY = fCodec->nextScanline();
-                if (is_coord_necessary(srcY, sampleY, dstHeight)) {
-                    void* dstPtr = SkTAddOffset<void>(dst, rowBytes * get_dst_coord(srcY, sampleY));
-                    if (1 != fCodec->getScanlines(dstPtr, 1, rowBytes)) {
-                        result = kIncompleteInput;
+                if (is_coord_necessary(srcY, sampleY, dstHeight, subsetY)) {
+                    void* pixelPtr = SkTAddOffset<void>(pixels,
+                            rowBytes * get_dst_coord(srcY, sampleY));
+                    if (1 != fCodec->getScanlines(pixelPtr, 1, rowBytes)) {
+                        result = SkCodec::kIncompleteInput;
                         break;
                     }
                 } else {
                     if (!fCodec->skipScanlines(1)) {
-                        result = kIncompleteInput;
+                        result = SkCodec::kIncompleteInput;
                         break;
                     }
                 }
             }
 
-            // We handle filling uninitialized memory here instead of in the parent class.
-            // The parent class does not know that we are sampling.
-            if (kIncompleteInput == result) {
-                const uint32_t fillValue = fCodec->getFillValue(requestedInfo.colorType(),
-                        requestedInfo.alphaType());
-                for (; y < srcHeight; y++) {
+            // We handle filling uninitialized memory here instead of using fCodec.
+            // fCodec does not know that we are sampling.
+            if (SkCodec::kIncompleteInput == result) {
+                const uint32_t fillValue = fCodec->getFillValue(info.colorType(),
+                        info.alphaType());
+                for (; y < fCodec->getInfo().height(); y++) {
                     int srcY = fCodec->outputScanline(y);
-                    if (is_coord_necessary(srcY, sampleY, dstHeight)) {
-                        void* dstRow = SkTAddOffset<void>(dst,
+                    if (is_coord_necessary(srcY, sampleY, dstHeight, subsetY)) {
+                        void* pixelPtr = SkTAddOffset<void>(pixels,
                                 rowBytes * get_dst_coord(srcY, sampleY));
-                        SkSampler::Fill(requestedInfo.makeWH(requestedInfo.width(), 1), dstRow,
-                                rowBytes, fillValue, options.fZeroInitialized);
-                    }
-                }
-                *rowsDecoded = dstHeight;
+                        SkSampler::Fill(info.makeWH(info.width(), 1), pixelPtr, rowBytes, fillValue,
+                                options.fZeroInitialized);
+                    }
+                }
             }
             return result;
         }
         case SkCodec::kNone_SkScanlineOrder: {
-            SkAutoMalloc storage(srcHeight * rowBytes);
+            SkAutoMalloc storage((subsetHeight - y0) * rowBytes);
             uint8_t* storagePtr = static_cast<uint8_t*>(storage.get());
-            int scanlines = fCodec->getScanlines(storagePtr, srcHeight, rowBytes);
-            storagePtr += Y0 * rowBytes;
-            scanlines -= Y0;
+            if (!fCodec->skipScanlines(subsetY + y0)) {
+                fCodec->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                        dstHeight, 0);
+                return SkCodec::kIncompleteInput;
+            }
+            int scanlines = fCodec->getScanlines(storagePtr, subsetHeight - y0, rowBytes);
             int y = 0;
-            while (y < dstHeight && scanlines > 0) {
-                memcpy(dst, storagePtr, rowBytes);
+            void* pixelPtr = pixels;
+            while (y < dstHeight) {
+                memcpy(pixelPtr, storagePtr, info.minRowBytes());
                 storagePtr += sampleY * rowBytes;
-                dst = SkTAddOffset<void>(dst, rowBytes);
-                scanlines -= sampleY;
+                pixelPtr = SkTAddOffset<void>(pixelPtr, rowBytes);
                 y++;
             }
-            if (y < dstHeight) {
+            if (scanlines < dstHeight) {
                 // fCodec has already handled filling uninitialized memory.
-                *rowsDecoded = dstHeight;
-                return kIncompleteInput;
-            }
-            return kSuccess;
+                return SkCodec::kIncompleteInput;
+            }
+            return SkCodec::kSuccess;
         }
         default:
             SkASSERT(false);
-            return kUnimplemented;
-    }
-}
-
-uint32_t SkScaledCodec::onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const {
-    return fCodec->onGetFillValue(colorType, alphaType);
-}
-
-SkCodec::SkScanlineOrder SkScaledCodec::onGetScanlineOrder() const {
-    return fCodec->onGetScanlineOrder();
-}
+            return SkCodec::kUnimplemented;
+    }
+}