Update Subset benches to support interlacing and fix bugs

bench/subset/SubsetZoomBench.cpp

Index: bench/subset/SubsetZoomBench.cpp
diff --git a/bench/subset/SubsetZoomBench.cpp b/bench/subset/SubsetZoomBench.cpp
index ffd86703ec2271e40fdc27c1679fe914f4b958ac..901fbb6082c4b83dc776228d6db33cafb7708378 100644
--- a/bench/subset/SubsetZoomBench.cpp
+++ b/bench/subset/SubsetZoomBench.cpp
@@ -62,14 +62,20 @@ void SubsetZoomBench::onDraw(int n, SkCanvas* canvas) {
         for (int count = 0; count < n; count++) {
             SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(fStream->duplicate()));
             const SkImageInfo info = codec->getInfo().makeColorType(fColorType);
-            SkAutoTDeleteArray<uint8_t> row(new uint8_t[info.minRowBytes()]);
-            codec->startScanlineDecode(info, nullptr, colors, &colorCount);
+            SkAutoTDeleteArray<uint8_t> row(nullptr);
+            if (codec->getScanlineOrder() == SkCodec::kTopDown_SkScanlineOrder) {
+                row.reset(new uint8_t[info.minRowBytes()]);
+            }
 
             const int centerX = info.width() / 2;
             const int centerY = info.height() / 2;
             int w = fSubsetWidth;
             int h = fSubsetHeight;
             do {
+                SkDEBUGCODE(SkCodec::Result result = )
+                codec->startScanlineDecode(info, nullptr, colors, &colorCount);
+                SkASSERT(SkCodec::kSuccess == result);
+
                 const int subsetStartX = SkTMax(0, centerX - w / 2);
                 const int subsetStartY = SkTMax(0, centerY - h / 2);
                 const int subsetWidth = SkTMin(w, info.width() - subsetStartX);
@@ -81,12 +87,44 @@ void SubsetZoomBench::onDraw(int n, SkCanvas* canvas) {
                 alloc_pixels(&bitmap, subsetInfo, colors, colorCount);

[scroggo, 2015/10/08 18:29:08]

Since we do a new allocation each time, we can always do this after
startScanlineDecode, so colorCount (as well as colors) is always initialized.

[msarett, 2015/10/08 18:52:42]

Acknowledged.

 
                 uint32_t bpp = info.bytesPerPixel();
-                codec->skipScanlines(subsetStartY);
-                for (int y = 0; y < subsetHeight; y++) {
-                    codec->getScanlines(row.get(), 1, 0);
-                    memcpy(bitmap.getAddr(0, y), row.get() + subsetStartX * bpp,
-                            subsetWidth * bpp);
+
+                SkDEBUGCODE(result = ) codec->skipScanlines(subsetStartY);
+                SkASSERT(SkCodec::kSuccess == result);
+
+                switch (codec->getScanlineOrder()) {
+                    case SkCodec::kTopDown_SkScanlineOrder:
+                        for (int y = 0; y < subsetHeight; y++) {
+                            SkDEBUGCODE(result = ) codec->getScanlines(row.get(), 1, 0);
+                            SkASSERT(SkCodec::kSuccess == result);
+
+                            memcpy(bitmap.getAddr(0, y), row.get() + subsetStartX * bpp,
+                                    subsetWidth * bpp);
+                        }
+                        break;
+                    case SkCodec::kNone_SkScanlineOrder: {
+                        // decode all scanlines that intersect the subset, and copy the subset
+                        // into the output.
+                        SkImageInfo stripeInfo = info.makeWH(info.width(), subsetHeight);
+                        SkBitmap stripeBm;
+                        alloc_pixels(&stripeBm, stripeInfo, colors, colorCount);

[scroggo, 2015/10/08 18:29:08]

Here and in SubsetTranslateBench, we're doing some extra work to create a bitmap
plus its colortable (in index8). We could instead just do some kind of malloc.
Then we'd have to write more code to do all the calculations that bitmap does
for us. I went with the simpler option, since this test had errors in the
past...

[msarett, 2015/10/08 18:52:41]

This is probably the right decision.

In general, I don't like SkBitmap and SkColorTable and use them as little as
possible.  I think we are stuck with Bitmaps anyway for the Android API so we
might as well benchmark them.

+
+                        SkDEBUGCODE(result = ) codec->getScanlines(stripeBm.getPixels(),
+                                subsetHeight, stripeBm.rowBytes());
+                        SkASSERT(SkCodec::kSuccess == result);
+
+                        for (int y = 0; y < subsetHeight; y++) {
+                            memcpy(bitmap.getAddr(0, y),
+                                   stripeBm.getAddr(subsetStartX, y),
+                                   subsetWidth * bpp);
+                        }
+                        break;
+                    }
+                    default:
+                        // We currently are only testing kTopDown and kNone, which are the only
+                        // two used by the subsets we care about. skbug.com/4428
+                        SkASSERT(false);
                 }
+
                 w <<= 1;
                 h <<= 1;
             } while (w < 2 * info.width() || h < 2 * info.height());
@@ -95,7 +133,7 @@ void SubsetZoomBench::onDraw(int n, SkCanvas* canvas) {
         for (int count = 0; count < n; count++) {
             int width, height;
             SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(fStream));
-            decoder->buildTileIndex(fStream->duplicate(), &width, &height);
+            SkAssertResult(decoder->buildTileIndex(fStream->duplicate(), &width, &height));
 
             const int centerX = width / 2;
             const int centerY = height / 2;
@@ -109,7 +147,7 @@ void SubsetZoomBench::onDraw(int n, SkCanvas* canvas) {
                 SkBitmap bitmap;
                 SkIRect rect = SkIRect::MakeXYWH(subsetStartX, subsetStartY, subsetWidth,
                         subsetHeight);
-                decoder->decodeSubset(&bitmap, rect, fColorType);
+                SkAssertResult(decoder->decodeSubset(&bitmap, rect, fColorType));
                 w <<= 1;
                 h <<= 1;
             } while (w < 2 * width || h < 2 * height);