SkScaledCodec class

src/codec/SkCodec_libpng.cpp

Index: src/codec/SkCodec_libpng.cpp
diff --git a/src/codec/SkCodec_libpng.cpp b/src/codec/SkCodec_libpng.cpp
index 553233de12117ea8ccebcdfd261a720b8e721412..79b2c0ea35d18ad27d7db73a600d8c973faac9e0 100644
--- a/src/codec/SkCodec_libpng.cpp
+++ b/src/codec/SkCodec_libpng.cpp
@@ -471,10 +471,12 @@ SkCodec::Result SkPngCodec::initializeSwizzler(const SkImageInfo& requestedInfo,
     // Copy the color table to the client if they request kIndex8 mode
     copy_color_table(requestedInfo, fColorTable, ctable, ctableCount);
 
+    int sampleX = this->getInfo().width() / requestedInfo.width();

[scroggo, 2015/07/30 17:53:01]

This should also be in some central place, to be shared with other decoders.

+
     // Create the swizzler.  SkPngCodec retains ownership of the color table.
     const SkPMColor* colors = fColorTable ? fColorTable->readColors() : NULL;
     fSwizzler.reset(SkSwizzler::CreateSwizzler(fSrcConfig, colors, requestedInfo,
-            dst, rowBytes, options.fZeroInitialized));
+            dst, rowBytes, options.fZeroInitialized, sampleX));
     if (!fSwizzler) {
         // FIXME: CreateSwizzler could fail for another reason.
         return kUnimplemented;
@@ -597,7 +599,7 @@ public:
         , fCodec(codec)
         , fHasAlpha(false)
     {
-        fStorage.reset(dstInfo.width() * SkSwizzler::BytesPerPixel(fCodec->fSrcConfig));
+        fStorage.reset(fCodec->getInfo().width() * SkSwizzler::BytesPerPixel(fCodec->fSrcConfig));
         fSrcRow = static_cast<uint8_t*>(fStorage.get());
     }
 
@@ -634,6 +636,10 @@ public:
 
     bool onReallyHasAlpha() const override { return fHasAlpha; }
 
+    bool onIsHardToSample() override {
+        return false;
+    }
+
 private:
     SkAutoTDelete<SkPngCodec>   fCodec;
     bool                        fHasAlpha;
@@ -653,7 +659,7 @@ public:
         , fCurrentRow(0)
         , fHeight(dstInfo.height())
     {
-        fSrcRowBytes = dstInfo.width() * SkSwizzler::BytesPerPixel(fCodec->fSrcConfig);
+        fSrcRowBytes = codec->getInfo().width() * SkSwizzler::BytesPerPixel(fCodec->fSrcConfig);
         fGarbageRow.reset(fSrcRowBytes);
         fGarbageRowPtr = static_cast<uint8_t*>(fGarbageRow.get());
     }
@@ -708,6 +714,10 @@ public:
 
     bool onReallyHasAlpha() const override { return fHasAlpha; }
 
+    bool onIsHardToSample() override {
+        return true;
+    }
+
 private:
     SkAutoTDelete<SkPngCodec>   fCodec;
     bool                        fHasAlpha;
@@ -727,9 +737,14 @@ SkScanlineDecoder* SkPngCodec::onGetScanlineDecoder(const SkImageInfo& dstInfo,
         SkCodecPrintf("no conversion possible\n");
         return NULL;
     }
+    Options scaledOptions = options;

[scroggo, 2015/07/30 17:53:01]

It looks like we do not modify scaledOptions, so we could just use options.

[emmaleer, 2015/07/30 22:27:55]

Acknowledged.

     // Check to see if scaling was requested.
-    if (dstInfo.dimensions() != this->getInfo().dimensions()) {
-        return NULL;
+    if(dstInfo.dimensions() != this->getInfo().dimensions()) {
+        // the caller is sampling
+        // heights must be equal as SkCodec_libpng has no native y sampling

[scroggo, 2015/07/30 17:53:01]

What about widths? We don't want them to request a width that is greater than
getInfo().width(), for example. Can we support all widths that are smaller?

[emmaleer, 2015/07/30 22:27:55]

Good point. I've added a check to only allow smaller or equal widths.

+        if (dstInfo.height() != this->getInfo().height()) {
+            return NULL;
+        }
     }
     // Create a new SkPngCodec, to be owned by the scanline decoder.
     SkStream* stream = this->stream()->duplicate();
@@ -744,7 +759,7 @@ SkScanlineDecoder* SkPngCodec::onGetScanlineDecoder(const SkImageInfo& dstInfo,
     // Note: We set dst to NULL since we do not know it yet. rowBytes is not needed,
     // since we'll be manually updating the dstRow, but the SkSwizzler requires it to
     // be at least dstInfo.minRowBytes.
-    if (codec->initializeSwizzler(dstInfo, NULL, dstInfo.minRowBytes(), options, ctable,
+    if (codec->initializeSwizzler(dstInfo, NULL, dstInfo.minRowBytes(), scaledOptions, ctable,
             ctableCount) != kSuccess) {
         SkCodecPrintf("failed to initialize the swizzler.\n");
         return NULL;