SkScaledCodec class

src/codec/SkCodec_libpng.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 "SkCodec_libpng.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 453 matching lines @@
             }
             break;
         default:
             //would have exited before now if the colorType was supported by png
             SkASSERT(false);
     }  
 
     // 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;
     }
     return kSuccess;
 }
 
 
 bool SkPngCodec::handleRewind() {
     switch (this->rewindIfNeeded()) {
@@ skipping 102 matching lines @@
     return kSuccess;
 }
 
 class SkPngScanlineDecoder : public SkScanlineDecoder {
 public:
     SkPngScanlineDecoder(const SkImageInfo& dstInfo, SkPngCodec* codec)
         : INHERITED(dstInfo)
         , 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());
     }
 
     SkCodec::Result onGetScanlines(void* dst, int count, size_t rowBytes) override {
         if (setjmp(png_jmpbuf(fCodec->fPng_ptr))) {
             SkCodecPrintf("setjmp long jump!\n");
             return SkCodec::kInvalidInput;
         }
 
         for (int i = 0; i < count; i++) {
@@ skipping 16 matching lines @@
         //calling png_read_rows in a loop is insignificantly slower than calling it once with count 
         //as png_read_rows has it's own loop which calls png_read_row count times.
         for (int i = 0; i < count; i++) {
             png_read_rows(fCodec->fPng_ptr, &fSrcRow, png_bytepp_NULL, 1);
         }
         return SkCodec::kSuccess;
     }
 
     bool onReallyHasAlpha() const override { return fHasAlpha; }
 
+    bool onIsHardToSample() override {
+        return false;
+    }
+
 private:
     SkAutoTDelete<SkPngCodec>   fCodec;
     bool                        fHasAlpha;
     SkAutoMalloc                fStorage;
     uint8_t*                    fSrcRow;
 
     typedef SkScanlineDecoder INHERITED;
 };
 
 
 class SkPngInterlacedScanlineDecoder : public SkScanlineDecoder {
 public:
     SkPngInterlacedScanlineDecoder(const SkImageInfo& dstInfo, SkPngCodec* codec)
         : INHERITED(dstInfo)
         , fCodec(codec)
         , fHasAlpha(false)
         , 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());
     }
 
     SkCodec::Result onGetScanlines(void* dst, int count, size_t dstRowBytes) override {
         //rewind stream if have previously called onGetScanlines, 
         //since we need entire progressive image to get scanlines
         if (!fCodec->handleRewind()) {
             return SkCodec::kCouldNotRewind;
         }
@@ skipping 34 matching lines @@
     }
 
     SkCodec::Result onSkipScanlines(int count) override {
         //when ongetScanlines is called it will skip to fCurrentRow
         fCurrentRow += count;
         return SkCodec::kSuccess;
     }
 
     bool onReallyHasAlpha() const override { return fHasAlpha; }
 
+    bool onIsHardToSample() override {
+        return true;
+    }
+
 private:
     SkAutoTDelete<SkPngCodec>   fCodec;
     bool                        fHasAlpha;
     int                         fCurrentRow;
     int                         fHeight;
     size_t                      fSrcRowBytes;
     SkAutoMalloc                fGarbageRow;
     uint8_t*                    fGarbageRowPtr;
 
     typedef SkScanlineDecoder INHERITED;
 };
 
 
 SkScanlineDecoder* SkPngCodec::onGetScanlineDecoder(const SkImageInfo& dstInfo,
         const Options& options, SkPMColor ctable[], int* ctableCount) {
     if (!conversion_possible(dstInfo, this->getInfo())) {
         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();
     if (!stream) {
         return NULL;
     }
     SkAutoTDelete<SkPngCodec> codec (static_cast<SkPngCodec*>(SkPngCodec::NewFromStream(stream)));
     if (!codec) {
         return NULL;
     }
 
     // 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;
     }
 
     SkASSERT(codec->fNumberPasses != INVALID_NUMBER_PASSES);
     if (codec->fNumberPasses > 1) {
         // interlaced image
         return SkNEW_ARGS(SkPngInterlacedScanlineDecoder, (dstInfo, codec.detach()));
     }
 
     return SkNEW_ARGS(SkPngScanlineDecoder, (dstInfo, codec.detach()));
 }