Refactor SkBitmapRegionDecoderInterface for Android

tools/SkBitmapRegionCanvas.cpp

Index: tools/SkBitmapRegionCanvas.cpp
diff --git a/tools/SkBitmapRegionCanvas.cpp b/tools/SkBitmapRegionCanvas.cpp
index f9c9573c445c2c3e7a86704cbf09fd11c7fa611b..3b1a039a73e0666d41a89f1edbe71ff7e6472b16 100644
--- a/tools/SkBitmapRegionCanvas.cpp
+++ b/tools/SkBitmapRegionCanvas.cpp
@@ -15,125 +15,101 @@ SkBitmapRegionCanvas::SkBitmapRegionCanvas(SkCodec* decoder)
     , fDecoder(decoder)
 {}
 
-/*
- * 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) {
+bool SkBitmapRegionCanvas::prepareRegion(const SkIRect& desiredSubset,
+                                         int sampleSize,
+                                         SkColorType dstColorType,
+                                         bool requireUnpremul,
+                                         SkImageInfo* outInfo) {
     // Reject color types not supported by this method
     if (kIndex_8_SkColorType == dstColorType || kGray_8_SkColorType == dstColorType) {

[scroggo, 2015/10/27 15:00:50]

Should we also check for requireUnpremul here? I suppose it could be fine if we
end up not needing to do any drawing? And maybe we could even do index 8 if we
don't need to call cropBitmap? May not be worth doing all the special casing?

         SkCodecPrintf("Error: Color type not supported.\n");
-        return nullptr;
+        return false;
     }
 
     // Fix the input sampleSize if necessary.
     if (sampleSize < 1) {
         sampleSize = 1;
     }
+    fSampleSize = sampleSize;
 
-    // The size of the output bitmap is determined by the size of the
-    // requested subset, not by the size of the intersection of the subset
-    // and the image dimensions.
-    // If inputX is negative, we will need to place decoded pixels into the
-    // output bitmap starting at a left offset.  Call this outX.
-    // If outX is non-zero, subsetX must be zero.
-    // If inputY is negative, we will need to place decoded pixels into the
-    // output bitmap starting at a top offset.  Call this outY.
-    // If outY is non-zero, subsetY must be zero.
-    int outX;
-    int outY;
-    SkIRect subset = SkIRect::MakeXYWH(inputX, inputY, inputWidth, inputHeight);
-    SubsetType type = adjust_subset_rect(fDecoder->getInfo().dimensions(), &subset, &outX, &outY);
-    if (SubsetType::kOutside_SubsetType == type) {
-        return nullptr;
+    fSubset = desiredSubset;
+    fSubsetType = adjust_subset_rect(fDecoder->getInfo().dimensions(), &fSubset, &fOutX, &fOutY);
+    if (SubsetType::kOutside_SubsetType == fSubsetType) {
+        return false;
     }
 
-    // Create the image info for the decode
+    // Create the image info.
     SkAlphaType dstAlphaType = fDecoder->getInfo().alphaType();
-    if (kUnpremul_SkAlphaType == dstAlphaType) {
-        dstAlphaType = kPremul_SkAlphaType;
+    if (kOpaque_SkAlphaType != dstAlphaType) {
+        dstAlphaType = requireUnpremul ? kUnpremul_SkAlphaType : kPremul_SkAlphaType;
+    }
+    fOutInfo = SkImageInfo::Make(get_scaled_dimension(desiredSubset.width(), sampleSize),
+            get_scaled_dimension(desiredSubset.height(), sampleSize), dstColorType, dstAlphaType);
+    *outInfo = fOutInfo;
+
+    // The decoder does not know anything about the scale that we are applying.
+    fDecodeInfo = fOutInfo.makeWH(this->width(), this->height());
+
+    // Check that we can convert to the requested color and alpha types.
+    return conversion_possible(fOutInfo, fDecoder->getInfo());
+}
+
+bool SkBitmapRegionCanvas::decodeRegion(SkBitmap& bitmap) {
+    if (fOutInfo.isEmpty()) {
+        SkCodecPrintf("Error: Call prepareRegion() first.");
+        return false;
+    }
+
+    if (bitmap.width() < fOutInfo.width() || bitmap.height() < fOutInfo.height() ||
+            bitmap.colorType() != fOutInfo.colorType()) {
+        SkCodecPrintf("Error: Invalid size or color type for input bitmap.");
+        return false;
     }
-    SkImageInfo decodeInfo = SkImageInfo::Make(this->width(), this->height(),
-            dstColorType, dstAlphaType);
+    bitmap.setAlphaType(fOutInfo.alphaType());
 
     // Start the scanline decoder
-    SkCodec::Result r = fDecoder->startScanlineDecode(decodeInfo);
+    SkCodec::Result r = fDecoder->startScanlineDecode(fDecodeInfo);
     if (SkCodec::kSuccess != r) {
         SkCodecPrintf("Error: Could not start scanline decoder.\n");
-        return nullptr;
+        return false;
     }
 
     // Allocate a bitmap for the unscaled decode
     SkBitmap tmp;
-    SkImageInfo tmpInfo = decodeInfo.makeWH(this->width(), subset.height());
+    SkImageInfo tmpInfo = fDecodeInfo.makeWH(this->width(), fSubset.height());
     if (!tmp.tryAllocPixels(tmpInfo)) {
         SkCodecPrintf("Error: Could not allocate pixels.\n");
-        return nullptr;
+        return false;
     }
 
     // Skip the unneeded rows
-    if (!fDecoder->skipScanlines(subset.y())) {
+    if (!fDecoder->skipScanlines(fSubset.y())) {
         SkCodecPrintf("Error: Failed to skip scanlines.\n");
-        return nullptr;
+        return false;
     }
 
     // Decode the necessary rows
-    fDecoder->getScanlines(tmp.getAddr(0, 0), subset.height(), tmp.rowBytes());
-
-    // Calculate the size of the output
-    const int outWidth = get_scaled_dimension(inputWidth, sampleSize);
-    const int outHeight = get_scaled_dimension(inputHeight, sampleSize);
-
-    // Initialize the destination bitmap
-    SkAutoTDelete<SkBitmap> bitmap(new SkBitmap());
-    SkImageInfo dstInfo = decodeInfo.makeWH(outWidth, outHeight);
-    if (!bitmap->tryAllocPixels(dstInfo)) {
-        SkCodecPrintf("Error: Could not allocate pixels.\n");
-        return nullptr;
-    }
+    fDecoder->getScanlines(tmp.getAddr(0, 0), fSubset.height(), tmp.rowBytes());
 
     // 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 (SubsetType::kPartiallyInside_SubsetType == type) {
-        bitmap->eraseColor(0);
+    if (SubsetType::kPartiallyInside_SubsetType == fSubsetType) {
+        bitmap.eraseColor(0);
     }
 
     // Use a canvas to crop and scale to the destination bitmap
-    SkCanvas canvas(*bitmap);
+    SkCanvas canvas(bitmap);
     // TODO (msarett): Maybe we can take advantage of the fact that SkRect uses floats?
-    SkRect src = SkRect::MakeXYWH((SkScalar) subset.x(), (SkScalar) 0,
-            (SkScalar) subset.width(), (SkScalar) subset.height());
-    SkRect dst = SkRect::MakeXYWH((SkScalar) (outX / sampleSize), (SkScalar) (outY / sampleSize),
-            (SkScalar) get_scaled_dimension(subset.width(), sampleSize),
-            (SkScalar) get_scaled_dimension(subset.height(), sampleSize));
+    SkRect src = SkRect::MakeXYWH((SkScalar) fSubset.x(), (SkScalar) 0,
+            (SkScalar) fSubset.width(), (SkScalar) fSubset.height());
+    SkRect dst = SkRect::MakeXYWH((SkScalar) (fOutX / fSampleSize),
+            (SkScalar) (fOutY / fSampleSize),
+            (SkScalar) get_scaled_dimension(fSubset.width(), fSampleSize),
+            (SkScalar) get_scaled_dimension(fSubset.height(), fSampleSize));
     SkPaint paint;
     // Overwrite the dst with the src pixels
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     // TODO (msarett): Test multiple filter qualities.  kNone is the default.
     canvas.drawBitmapRect(tmp, src, dst, &paint);
 
-    return bitmap.detach();
-}
-
-bool SkBitmapRegionCanvas::conversionSupported(SkColorType colorType) {
-    // 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());
+    return true;
 }