Fill incomplete images in SkCodec parent class

src/codec/SkCodec_libgif.cpp

Index: src/codec/SkCodec_libgif.cpp
diff --git a/src/codec/SkCodec_libgif.cpp b/src/codec/SkCodec_libgif.cpp
index e6d1141669b69ee122053a61b80bcf643b54b6ea..f72150a19bea6fdb363a30f27c1720f757c4334f 100644
--- a/src/codec/SkCodec_libgif.cpp
+++ b/src/codec/SkCodec_libgif.cpp
@@ -96,31 +96,6 @@ static uint32_t find_trans_index(const SavedImage& image) {
     return SK_MaxU32;
 }
 
-static inline uint32_t ceil_div(uint32_t a, uint32_t b) {
-    return (a + b - 1) / b;
-}
-
-/*
- * Gets the output row corresponding to the encoded row for interlaced gifs
- */
-static uint32_t get_output_row_interlaced(uint32_t encodedRow, uint32_t height) {
-    SkASSERT(encodedRow < height);
-    // First pass
-    if (encodedRow * 8 < height) {
-        return encodedRow * 8;
-    }
-    // Second pass
-    if (encodedRow * 4 < height) {
-        return 4 + 8 * (encodedRow - ceil_div(height, 8));
-    }
-    // Third pass
-    if (encodedRow * 2 < height) {
-        return 2 + 4 * (encodedRow - ceil_div(height, 4));
-    }
-    // Fourth pass
-    return 1 + 2 * (encodedRow - ceil_div(height, 2));
-}
-
 /*
  * This function cleans up the gif object after the decode completes
  * It is used in a SkAutoTCallIProc template
@@ -492,11 +467,8 @@ SkCodec::Result SkGifCodec::initializeSwizzler(const SkImageInfo& dstInfo,
     return kUnimplemented;
 }
 
-SkCodec::Result SkGifCodec::readRow() {
-    if (GIF_ERROR == DGifGetLine(fGif, fSrcBuffer.get(), fFrameDims.width())) {
-        return kIncompleteInput;
-    }
-    return kSuccess;
+bool SkGifCodec::readRow() {
+    return GIF_ERROR != DGifGetLine(fGif, fSrcBuffer.get(), fFrameDims.width());
 }
 
 /*
@@ -506,7 +478,8 @@ SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
                                         void* dst, size_t dstRowBytes,
                                         const Options& opts,
                                         SkPMColor* inputColorPtr,
-                                        int* inputColorCount) {
+                                        int* inputColorCount,
+                                        int* rowsDecoded) {
     Result result = this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, opts);
     if (kSuccess != result) {
         return result;
@@ -525,8 +498,8 @@ SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
 
         // Fill the background
         const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
-        SkSwizzler::Fill(dst, dstInfo, dstRowBytes, this->getInfo().height(),
-                fFillIndex, colorPtr, opts.fZeroInitialized);
+        SkSwizzler::Fill(dst, dstInfo, dstRowBytes, this->getFillValue(dstInfo.colorType(),
+                dstInfo.alphaType()), opts.fZeroInitialized);
 
         // Modify the dst pointer
         const int32_t dstBytesPerPixel = SkColorTypeBytesPerPixel(dstInfo.colorType());
@@ -538,49 +511,29 @@ SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
         }
     }
 
-    // Check the interlace flag and iterate over rows of the input
+    // Iterate over rows of the input
     uint32_t width = fFrameDims.width();
     uint32_t height = fFrameDims.height();
-    if (fGif->Image.Interlace) {
-        // In interlace mode, the rows of input are rearranged in
-        // the output image.  We a helper function to help us
-        // rearrange the decoded rows.
-        for (uint32_t y = 0; y < height; y++) {
-            if (kSuccess != this->readRow()) {
-                // Recover from error by filling remainder of image
-                memset(fSrcBuffer.get(), fFillIndex, width);
-                for (; y < height; y++) {
-                    void* dstRow = SkTAddOffset<void>(dst,
-                            dstRowBytes * get_output_row_interlaced(y, height));
-                    fSwizzler->swizzle(dstRow, fSrcBuffer.get());
-                }
-                return gif_error("Could not decode line.\n", kIncompleteInput);
-            }
-            void* dstRow = SkTAddOffset<void>(dst,
-                    dstRowBytes * get_output_row_interlaced(y, height));
-            fSwizzler->swizzle(dstRow, fSrcBuffer.get());
-        }
-    } else {
-        // Standard mode
-        void* dstRow = dst;
-        for (uint32_t y = 0; y < height; y++) {
-            if (kSuccess != this->readRow()) {
-                const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
-                SkSwizzler::Fill(dstRow, dstInfo, dstRowBytes,
-                        height - y, fFillIndex, colorPtr, opts.fZeroInitialized);
-                return gif_error("Could not decode line\n", kIncompleteInput);
-            }
-            fSwizzler->swizzle(dstRow, fSrcBuffer.get());
-            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
+    for (uint32_t y = 0; y < height; y++) {
+        if (!this->readRow()) {
+            *rowsDecoded = y;
+            return gif_error("Could not decode line.\n", kIncompleteInput);
         }
+        void* dstRow = SkTAddOffset<void>(dst, dstRowBytes * this->nextScanline(y));
+        fSwizzler->swizzle(dstRow, fSrcBuffer.get());
     }
     return kSuccess;
 }
 
+uint32_t SkGifCodec::onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const {
+    const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
+    return get_color_table_fill_value(colorType, colorPtr, fFillIndex);
+}
+
 SkCodec::Result SkGifCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options& opts, SkPMColor inputColorPtr[], int* inputColorCount) {
-    Result result = this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount,
-                                          this->options());
+
+    Result result = this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, this->options());
     if (kSuccess != result) {
         return result;
     }
@@ -611,60 +564,43 @@ SkCodec::Result SkGifCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
     return kSuccess;
 }
 
-SkCodec::Result SkGifCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {
+uint32_t SkGifCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {
+    int rowsBeforeFrame = 0;
+    int rowsAfterFrame = 0;
     if (fFrameIsSubset) {
         // Fill the requested rows
-        const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
-        SkSwizzler::Fill(dst, this->dstInfo(), rowBytes, count, fFillIndex,
-                         colorPtr, this->options().fZeroInitialized);
+        SkSwizzler::Fill(dst, this->dstInfo().makeWH(this->dstInfo().width(), count), rowBytes,
+                this->onGetFillValue(this->dstInfo().colorType(), this->dstInfo().alphaType()),
+                this->options().fZeroInitialized);
 
         // Do nothing for rows before the image frame
-        // FIXME: nextScanline is not virtual, so using "INHERITED" does not change
-        // behavior. Was the intent to call this->INHERITED::onNextScanline()? Same
-        // for the next call down below.
-        int rowsBeforeFrame = fFrameDims.top() - this->INHERITED::nextScanline();
-        if (rowsBeforeFrame > 0) {
-            count = SkTMin(0, count - rowsBeforeFrame);
-            dst = SkTAddOffset<void>(dst, rowBytes * rowsBeforeFrame);
-        }
+        // FIXME: Do we handle fFrameIsSubset properly for interlaced images?
+        rowsBeforeFrame = SkTMax(0, fFrameDims.top() - this->nextScanline());
+        count = SkTMax(0, count - rowsBeforeFrame);
+        dst = SkTAddOffset<void>(dst, rowBytes * rowsBeforeFrame);
 
         // Do nothing for rows after the image frame
-        int rowsAfterFrame = this->INHERITED::nextScanline() + count - fFrameDims.bottom();
-        if (rowsAfterFrame > 0) {
-            count = SkTMin(0, count - rowsAfterFrame);
-        }
+        rowsAfterFrame = SkTMax(0, this->nextScanline() + count - fFrameDims.bottom());
+        count = SkTMax(0, count - rowsAfterFrame);
 
-            // Adjust dst pointer for left offset
+        // Adjust dst pointer for left offset
         int bpp = SkColorTypeBytesPerPixel(this->dstInfo().colorType()) * fFrameDims.left();
         dst = SkTAddOffset<void>(dst, bpp);
     }
 
     for (int i = 0; i < count; i++) {
-        if (kSuccess != this->readRow()) {
-            const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
-            SkSwizzler::Fill(dst, this->dstInfo(), rowBytes, count - i, fFillIndex, colorPtr,
-                             this->options().fZeroInitialized);
-            return gif_error("Could not decode line\n", SkCodec::kIncompleteInput);
+        if (!this->readRow()) {
+            return i + rowsBeforeFrame;
         }
         fSwizzler->swizzle(dst, fSrcBuffer.get());
         dst = SkTAddOffset<void>(dst, rowBytes);
     }
-    return SkCodec::kSuccess;
+    return count + rowsBeforeFrame + rowsAfterFrame;
 }
 
 SkCodec::SkScanlineOrder SkGifCodec::onGetScanlineOrder() const {
     if (fGif->Image.Interlace) {
         return kOutOfOrder_SkScanlineOrder;
-    } else {
-        return kTopDown_SkScanlineOrder;
     }
+    return kTopDown_SkScanlineOrder;
 }
-
-int SkGifCodec::onNextScanline() const {
-    if (fGif->Image.Interlace) {
-        return get_output_row_interlaced(this->INHERITED::onNextScanline(), this->dstInfo().height());
-    } else {
-        return this->INHERITED::onNextScanline();
-    }
-}
-