Implementation of SkBitmapRegionDecoder using SkAndroidCodec

tools/SkBitmapRegionCanvas.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 "SkBitmapRegionCanvas.h"
 #include "SkCanvas.h"
 #include "SkCodecPriv.h"
 #include "SkCodecTools.h"
 
 SkBitmapRegionCanvas::SkBitmapRegionCanvas(SkCodec* decoder)
     : INHERITED(decoder->getInfo().width(), decoder->getInfo().height())
     , fDecoder(decoder)
 {}
 
 /*
- * Chooses the correct image subset offsets and dimensions for the partial decode.

[msarett, 2015/10/12 18:42:36]

Moved to SkCodecTools.h

The only change is that this is now "inline" instead of "static".

- *
- * @return true if the subset is completely contained within the image
- *         false otherwise
- */
-static bool set_subset_region(int inputOffset, int inputDimension,
-        int imageOriginalDimension, int* imageSubsetOffset, int* outOffset,
-        int* imageSubsetDimension) {
-
-    // This must be at least zero, we can't start decoding the image at a negative coordinate.
-    *imageSubsetOffset = SkTMax(0, inputOffset);
-
-    // If inputOffset is less than zero, we decode to an offset location in the output bitmap.
-    *outOffset = *imageSubsetOffset - inputOffset;
-
-    // Use imageSusetOffset to make sure we don't decode pixels past the edge of the image.
-    // Use outOffset to make sure we don't decode pixels past the edge of the region.
-    *imageSubsetDimension = SkTMin(imageOriginalDimension - *imageSubsetOffset,
-            inputDimension - *outOffset);
-
-    return (*outOffset == 0) && (*imageSubsetDimension == inputDimension);
-}
-
-/*
  * Three differences from the Android version:
  *     Returns a Skia bitmap instead of an Android bitmap.
  *     Android version attempts to reuse a recycled bitmap.
  *     Removed the options object and used parameters for color type and
  *     sample size.
  */
 SkBitmap* SkBitmapRegionCanvas::decodeRegion(int inputX, int inputY,
                                              int inputWidth, int inputHeight,
                                              int sampleSize,
                                              SkColorType dstColorType) {
     // Reject color types not supported by this method
     if (kIndex_8_SkColorType == dstColorType || kGray_8_SkColorType == dstColorType) {
         SkCodecPrintf("Error: Color type not supported.\n");
         return nullptr;
     }
 
+    // Fix the input sampleSize if necessary.

[msarett, 2015/10/12 18:42:36]

Android does not set a default sampleSize.  We should fix this is Android, but
also catch it here to be robust.

+    if (sampleSize < 1) {
+        sampleSize = 1;
+    }
+
     // The client may not necessarily request a region that is fully within
     // the image.  We may need to do some calculation to determine what part
     // of the image to decode.
 
     // The left offset of the portion of the image we want, where zero
     // indicates the left edge of the image.
     int imageSubsetX;
 
     // The size of the output bitmap is determined by the size of the
     // requested region, not by the size of the intersection of the region
@@ skipping 32 matching lines @@
         return nullptr;
     }
 
     // Create the image info for the decode
     SkAlphaType dstAlphaType = fDecoder->getInfo().alphaType();
     if (kUnpremul_SkAlphaType == dstAlphaType) {
         dstAlphaType = kPremul_SkAlphaType;
     }
     SkImageInfo decodeInfo = SkImageInfo::Make(this->width(), this->height(),
             dstColorType, dstAlphaType);
-    
+
     // Start the scanline decoder
     SkCodec::Result r = fDecoder->startScanlineDecode(decodeInfo);
     if (SkCodec::kSuccess != r) {
         SkCodecPrintf("Error: Could not start scanline decoder.\n");
         return nullptr;
     }
 
     // Allocate a bitmap for the unscaled decode
     SkBitmap tmp;
     SkImageInfo tmpInfo = decodeInfo.makeWH(this->width(), imageSubsetHeight);
@@ skipping 23 matching lines @@
         return nullptr;
     }
 
     // Zero the bitmap if the region is not completely within the image.
     // TODO (msarett): Can we make this faster by implementing it to only
     //                 zero parts of the image that we won't overwrite with
     //                 pixels?
     // TODO (msarett): This could be skipped if memory is zero initialized.
     //                 This would matter if this code is moved to Android and
     //                 uses Android bitmaps.
-    if (imageContainsEntireSubset) {
+    if (!imageContainsEntireSubset) {

[msarett, 2015/10/12 18:42:36]

Oops.

         bitmap->eraseColor(0);
     }
 
     // Use a canvas to crop and scale to the destination bitmap
     SkCanvas canvas(*bitmap);
     // TODO (msarett): Maybe we can take advantage of the fact that SkRect uses floats?
     SkRect src = SkRect::MakeXYWH((SkScalar) imageSubsetX, (SkScalar) 0,
             (SkScalar) imageSubsetWidth, (SkScalar) imageSubsetHeight);
     SkRect dst = SkRect::MakeXYWH((SkScalar) (outX / sampleSize), (SkScalar) (outY / sampleSize),
             (SkScalar) get_scaled_dimension(imageSubsetWidth, sampleSize),
@@ skipping 11 matching lines @@
     // SkCanvas does not draw to these color types.
     if (kIndex_8_SkColorType == colorType || kGray_8_SkColorType == colorType) {
         return false;
     }
 
     // FIXME: Call virtual function when it lands.
     SkImageInfo info = SkImageInfo::Make(0, 0, colorType, fDecoder->getInfo().alphaType(),
             fDecoder->getInfo().profileType());
     return conversion_possible(info, fDecoder->getInfo());
 }