Revert of Change quality settings on SkImageDecoder_libjpeg

src/images/SkImageDecoder_libjpeg.cpp

 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkImageDecoder.h"
 #include "SkImageEncoder.h"
@@ skipping 365 matching lines @@
  *  Common code for setting the error manager.
  */
 static void set_error_mgr(jpeg_decompress_struct* cinfo, skjpeg_error_mgr* errorManager) {
     SkASSERT(cinfo != nullptr);
     SkASSERT(errorManager != nullptr);
     cinfo->err = jpeg_std_error(errorManager);
     errorManager->error_exit = skjpeg_error_exit;
 }
 
 /**
+ *  Common code for turning off upsampling and smoothing. Turning these
+ *  off helps performance without showing noticable differences in the
+ *  resulting bitmap.
+ */
+static void turn_off_visual_optimizations(jpeg_decompress_struct* cinfo) {
+    SkASSERT(cinfo != nullptr);
+    /* this gives about 30% performance improvement. In theory it may
+       reduce the visual quality, in practice I'm not seeing a difference
+     */
+    cinfo->do_fancy_upsampling = 0;
+
+    /* this gives another few percents */
+    cinfo->do_block_smoothing = 0;
+}
+
+/**
  * Common code for setting the dct method.
  */
 static void set_dct_method(const SkImageDecoder& decoder, jpeg_decompress_struct* cinfo) {
     SkASSERT(cinfo != nullptr);
+#ifdef DCT_IFAST_SUPPORTED
+    if (decoder.getPreferQualityOverSpeed()) {
+        cinfo->dct_method = JDCT_ISLOW;
+    } else {
+        cinfo->dct_method = JDCT_IFAST;
+    }
+#else
     cinfo->dct_method = JDCT_ISLOW;
+#endif
 }
 
 SkColorType SkJPEGImageDecoder::getBitmapColorType(jpeg_decompress_struct* cinfo) {
     SkASSERT(cinfo != nullptr);
 
     SrcDepth srcDepth = k32Bit_SrcDepth;
     if (JCS_GRAYSCALE == cinfo->jpeg_color_space) {
         srcDepth = k8BitGray_SrcDepth;
     }
 
@@ skipping 148 matching lines @@
         can) much faster that we, just use their num/denom api to approximate
         the size.
     */
     int sampleSize = this->getSampleSize();
 
     set_dct_method(*this, &cinfo);
 
     SkASSERT(1 == cinfo.scale_num);
     cinfo.scale_denom = sampleSize;
 
+    turn_off_visual_optimizations(&cinfo);
+
     const SkColorType colorType = this->getBitmapColorType(&cinfo);
     const SkAlphaType alphaType = kAlpha_8_SkColorType == colorType ?
                                       kPremul_SkAlphaType : kOpaque_SkAlphaType;
 
     adjust_out_color_space_and_dither(&cinfo, colorType, *this);
 
     if (1 == sampleSize && SkImageDecoder::kDecodeBounds_Mode == mode) {
         // Assume an A8 bitmap is not opaque to avoid the check of each
         // individual pixel. It is very unlikely to be opaque, since
         // an opaque A8 bitmap would not be very interesting.
@@ skipping 305 matching lines @@
     if (!planes || !planes[0] || !rowBytes || !rowBytes[0]) { // Compute size only
         update_components_sizes(cinfo, componentSizes, kSizeForMemoryAllocation_SizeType);
         return true;
     }
 
     set_dct_method(*this, &cinfo);
 
     SkASSERT(1 == cinfo.scale_num);
     cinfo.scale_denom = 1;
 
+    turn_off_visual_optimizations(&cinfo);
+
 #ifdef ANDROID_RGB
     cinfo.dither_mode = JDITHER_NONE;
 #endif
 
     /*  image_width and image_height are the original dimensions, available
         after jpeg_read_header(). To see the scaled dimensions, we have to call
         jpeg_start_decompress(), and then read output_width and output_height.
     */
     if (!jpeg_start_decompress(&cinfo)) {
         return return_false(cinfo, "start_decompress YUV8");
@@ skipping 54 matching lines @@
     jpeg_decompress_struct* cinfo = imageIndex->cinfo();
     // We have a new cinfo, so set the error mgr again.
     set_error_mgr(cinfo, &sk_err);
 
     // FIXME: This sets cinfo->out_color_space, which we may change later
     // based on the config in onDecodeSubset. This should be fine, since
     // jpeg_init_read_tile_scanline will check out_color_space again after
     // that change (when it calls jinit_color_deconverter).
     (void) this->getBitmapColorType(cinfo);
 
+    turn_off_visual_optimizations(cinfo);
+
     // instead of jpeg_start_decompress() we start a tiled decompress
     if (!imageIndex->startTileDecompress()) {
         return false;
     }
 
     SkASSERT(1 == cinfo->scale_num);
     fImageWidth = cinfo->output_width;
     fImageHeight = cinfo->output_height;
 
     if (width) {
@@ skipping 452 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 static SkImageEncoder* sk_libjpeg_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kJPEG_Type == t) ? new SkJPEGImageEncoder : nullptr;
 }
 
 static SkImageDecoder_DecodeReg gDReg(sk_libjpeg_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_jpeg);
 static SkImageEncoder_EncodeReg gEReg(sk_libjpeg_efactory);