Add subsetting to SkScanlineDecoder

src/codec/SkJpegCodec.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.h"
 #include "SkJpegCodec.h"
 #include "SkJpegDecoderMgr.h"
@@ skipping 159 matching lines @@
 }
 
 /*
  * Return a valid set of output dimensions for this decoder, given an input scale
  */
 SkISize SkJpegCodec::onGetScaledDimensions(float desiredScale) const {
     // libjpeg-turbo supports scaling by 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8, and 1/1, so we will
     // support these as well
     unsigned int num;
     unsigned int denom = 8;
-    if (desiredScale > 0.875f) {
+    if (desiredScale >= 0.9375) {
         num = 8;
-    } else if (desiredScale > 0.75f) {
+    } else if (desiredScale >= 0.8125) {
         num = 7;
-    } else if (desiredScale > 0.625f) {
+    } else if (desiredScale >= 0.6875f) {
         num = 6;
-    } else if (desiredScale > 0.5f) {
+    } else if (desiredScale >= 0.5625f) {
         num = 5;
-    } else if (desiredScale > 0.375f) {
+    } else if (desiredScale >= 0.4375f) {
         num = 4;
-    } else if (desiredScale > 0.25f) {
+    } else if (desiredScale >= 0.3125f) {
         num = 3;
-    } else if (desiredScale > 0.125f) {
+    } else if (desiredScale >= 0.1875f) {
         num = 2;
     } else {
         num = 1;
     }
 
     // Set up a fake decompress struct in order to use libjpeg to calculate output dimensions
     jpeg_decompress_struct dinfo;
     sk_bzero(&dinfo, sizeof(dinfo));
     dinfo.image_width = this->getInfo().width();
     dinfo.image_height = this->getInfo().height();
@@ skipping 170 matching lines @@
             convert_CMYK_to_RGBA(dstRow, dstInfo.width());
         }
 
         // Move to the next row
         dstRow = SkTAddOffset<JSAMPLE>(dstRow, dstRowBytes);
     }
 
     return kSuccess;
 }
 
-SkSampler* SkJpegCodec::getSampler(bool createIfNecessary) {
-    if (!createIfNecessary || fSwizzler) {
-        SkASSERT(!fSwizzler || (fSrcRow && static_cast<uint8_t*>(fStorage.get()) == fSrcRow));
-        return fSwizzler;
-    }
-
-    const SkImageInfo& info = this->dstInfo();
+void SkJpegCodec::initializeSwizzler(const SkImageInfo& dstInfo, const Options& options) {
     SkSwizzler::SrcConfig srcConfig;
-    switch (info.colorType()) {
+    switch (dstInfo.colorType()) {
         case kGray_8_SkColorType:
             srcConfig = SkSwizzler::kGray;
             break;
         case kRGBA_8888_SkColorType:
             srcConfig = SkSwizzler::kRGBX;
             break;
         case kBGRA_8888_SkColorType:
             srcConfig = SkSwizzler::kBGRX;
             break;
         case kRGB_565_SkColorType:
             srcConfig = SkSwizzler::kRGB_565;
             break;
         default:
             // This function should only be called if the colorType is supported by jpeg
             SkASSERT(false);
     }
 
-    fSwizzler.reset(SkSwizzler::CreateSwizzler(srcConfig, nullptr, info,
-                                               this->options().fZeroInitialized));
-    if (!fSwizzler) {
-        return nullptr;
+    fSwizzler.reset(SkSwizzler::CreateSwizzler(srcConfig, nullptr, dstInfo, options));
+    fStorage.reset(get_row_bytes(fDecoderMgr->dinfo()));
+    fSrcRow = static_cast<uint8_t*>(fStorage.get());
+}
+
+SkSampler* SkJpegCodec::getSampler(bool createIfNecessary) {
+    if (!createIfNecessary || fSwizzler) {
+        SkASSERT(!fSwizzler || (fSrcRow && static_cast<uint8_t*>(fStorage.get()) == fSrcRow));
+        return fSwizzler;
     }
 
-    fStorage.reset(get_row_bytes(fDecoderMgr->dinfo()));
-    fSrcRow = static_cast<uint8_t*>(fStorage.get());
+    this->initializeSwizzler(this->dstInfo(), this->options());
     return fSwizzler;
 }
 
 SkCodec::Result SkJpegCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         const Options& options, SkPMColor ctable[], int* ctableCount) {
     // Set the jump location for libjpeg errors
     if (setjmp(fDecoderMgr->getJmpBuf())) {
         SkCodecPrintf("setjmp: Error from libjpeg\n");
         return kInvalidInput;
     }
 
     // Check if we can decode to the requested destination and set the output color space
     if (!this->setOutputColorSpace(dstInfo)) {
         return kInvalidConversion;
     }
 
     // Remove objects used for sampling.
     fSwizzler.reset(nullptr);
     fSrcRow = nullptr;
     fStorage.free();
 
     // Now, given valid output dimensions, we can start the decompress
     if (!jpeg_start_decompress(fDecoderMgr->dinfo())) {
         SkCodecPrintf("start decompress failed\n");
         return kInvalidInput;
     }
 
+    // We will need a swizzler if we are performing a subset decode
+    if (options.fSubset) {
+        this->initializeSwizzler(dstInfo, options);
+    }
+
     return kSuccess;
 }
 
 int SkJpegCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {
     // Set the jump location for libjpeg errors
     if (setjmp(fDecoderMgr->getJmpBuf())) {
         return fDecoderMgr->returnFailure("setjmp", kInvalidInput);
     }
     // Read rows one at a time
     JSAMPLE* dstRow;
     if (fSwizzler) {
-        // write data to storage row, then sample using swizzler         
+        // write data to storage row, then sample using swizzler
         dstRow = fSrcRow;
     } else {
         // write data directly to dst
         dstRow = (JSAMPLE*) dst;
     }
 
     for (int y = 0; y < count; y++) {
         // Read row of the image
         uint32_t rowsDecoded = jpeg_read_scanlines(fDecoderMgr->dinfo(), &dstRow, 1);
         if (rowsDecoded != 1) {
@@ skipping 29 matching lines @@
 #endif
 
 bool SkJpegCodec::onSkipScanlines(int count) {
     // Set the jump location for libjpeg errors
     if (setjmp(fDecoderMgr->getJmpBuf())) {
         return fDecoderMgr->returnFalse("setjmp");
     }
 
     return count == jpeg_skip_scanlines(fDecoderMgr->dinfo(), count);
 }