Provides multiple implementations of Android's SkBitmapRegionDecoder

src/utils/SkBitmapRegionCanvas.cpp

Index: src/utils/SkBitmapRegionCanvas.cpp
diff --git a/src/utils/SkBitmapRegionCanvas.cpp b/src/utils/SkBitmapRegionCanvas.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..d6cf36bf3905c32000f31ddd2e9ae03ac214ef88
--- /dev/null
+++ b/src/utils/SkBitmapRegionCanvas.cpp
@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "SkBitmapRegionCanvas.h"
+#include "SkCanvas.h"
+#include "SkScanlineDecoder.h"
+
+SkBitmapRegionCanvas::SkBitmapRegionCanvas(SkScanlineDecoder* decoder)
+    : INHERITED(decoder->getInfo().width(), decoder->getInfo().height())
+    , fDecoder(decoder)
+{}
+
+/*
+ * This has several key differences from the Android version:
+ *     Returns a Skia bitmap instead of an Android bitmap.
+ *     Android version attempts to reuse a recycled bitmap.
+ */
+SkBitmap* SkBitmapRegionCanvas::decodeRegion(int input_x, int input_y,
+                                             int input_w, int input_h,
+                                             int sampleSize,
+                                             SkColorType colorType) {

[scroggo, 2015/08/13 16:53:07]

nit: Maybe this should be dstColorType?

[msarett, 2015/08/13 18:10:23]

Done.

+    // Reject color types not supported by this method
+    if (kIndex_8_SkColorType == colorType || kGray_8_SkColorType == colorType) {
+        SkDebugf("Error: Color type not supported.\n");
+        return NULL;
+    }
+
+    // Correct the output region if necessary
+    int left = SkTMax(0, input_x);
+    int leftOffset = left - input_x;
+    int top = SkTMax(0, input_y);
+    int topOffset = top - input_y;
+    int width = SkTMin(this->width() - left, input_w - leftOffset);
+    int height = SkTMin(this->height() - top, input_h - topOffset);
+    if (width <= 0 || height <= 0) {
+        SkDebugf("Error: Region must intersect part of the image.\n");
+        return NULL;
+    }
+
+    // Create the image info the decode
+    SkAlphaType alphaType = fDecoder->getInfo().alphaType();
+    if (kUnpremul_SkAlphaType == alphaType) {
+        alphaType = kPremul_SkAlphaType;
+    }
+    SkImageInfo decodeInfo = SkImageInfo::Make(this->width(), this->height(),
+            colorType, alphaType);
+    
+    // Start the scanline decoder
+    SkCodec::Result r = fDecoder->start(decodeInfo);
+    if (SkCodec::kSuccess != r) {
+        SkDebugf("Error: Could not start scanline decoder.\n");
+        return NULL;
+    }
+
+    // Allocate a bitmap for the unscaled decode
+    SkBitmap tmp;
+    SkImageInfo tmpInfo = decodeInfo.makeWH(this->width(), height);
+    if (!tmp.tryAllocPixels(tmpInfo)) {
+        SkDebugf("Error: Could not allocate pixels.\n");
+        return NULL;
+    }
+
+    // Skip the unneeded rows
+    SkCodec::Result result =
+            fDecoder->skipScanlines(top);
+    switch (result) {
+        case SkCodec::kSuccess:
+        case SkCodec::kIncompleteInput:

[scroggo, 2015/08/13 16:53:07]

It seems like if we got incomplete at this point, we have failed?

[msarett, 2015/08/13 18:10:23]

Agreed.  Changing this.

+            break;
+        default:
+            SkDebugf("Error: Failed to skip scanlines.\n");
+            return NULL;
+    }
+
+    // Decode the necessary rows
+    result = fDecoder->getScanlines(tmp.getAddr(0, 0), height,
+            tmp.rowBytes());
+    switch (result) {
+        case SkCodec::kSuccess:
+        case SkCodec::kIncompleteInput:
+            break;
+        default:
+            SkDebugf("Error: Failed to get scanlines.\n");
+            return NULL;
+    }
+
+    // Calculate the size of the output
+    int outWidth = SkTMax(1, input_w / sampleSize);
+    int outHeight = SkTMax(1, input_h / sampleSize);
+
+    // Initialize the destination bitmap
+    SkAutoTDelete<SkBitmap> bitmap(SkNEW(SkBitmap));
+    SkImageInfo dstInfo = decodeInfo.makeWH(outWidth, outHeight);
+    if (!bitmap->tryAllocPixels(dstInfo)) {
+        SkDebugf("Error: Could not allocate pixels.\n");
+        return NULL;
+    }
+    bitmap->eraseColor(0);

[msarett, 2015/08/13 15:16:34]

This was necessary for images with transparency.  Without this line, partially
transparent images are blended with the uninitialized memory already in the
bitmap.

I plan to explore if there is some mode I can change to make it overwrite the
bitmap completely.

I also need to figure out how to adjust the quality modes on drawBitmapRect.

[scroggo, 2015/08/13 16:53:07]

Seems like a good candidate for a FIXME.
How about SkXfermode::kSrc_Mode?
Do you mean the SkFilterQuality on the SkPaint?

[msarett, 2015/08/13 18:10:23]

Yes on all counts.  This has been added.  SkFilterQuality defaults to None but
we may want to test all of them at some point.

+
+    // Use a canvas to crop and scale to the destination bitmap
+    SkAutoTDelete<SkCanvas> canvas(SkNEW_ARGS(SkCanvas, (*bitmap)));
+    SkRect src = SkRect::MakeXYWH(left, 0, width, height);
+    SkRect dst = SkRect::MakeXYWH(leftOffset / sampleSize, topOffset / sampleSize,
+            SkTMax(1, width / sampleSize), SkTMax(1, height / sampleSize));
+    canvas->drawBitmapRect(tmp, src, dst, NULL);
+
+    return bitmap.detach();
+}