Use new jpeg_crop_scanlines() API to optimize jpeg subset decodes

This was adapted from:
https://codereview.chromium.org/1530933003

Subset Decode Runtime (Original / Optimized) on Nexus 6P
TopLeft     0.51x
TopRight    0.56x
Middle      0.71x
BottomLeft  0.79x
BottomRight 0.79x

BUG=skia:4256
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1719073002

Review URL: https://codereview.chromium.org/1719073002

3 files changed, 71 insertions, 4 deletions

diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index c4f7498f79..d7cfb37497 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -354,23 +354,28 @@ void SkCodec::fillIncompleteImage(const SkImageInfo& info, void* dst, size_t row
     const int linesRemaining = linesRequested - linesDecoded;
     SkSampler* sampler = this->getSampler(false);
 
+    int fillWidth = info.width();
+    if (fOptions.fSubset) {
+        fillWidth = fOptions.fSubset->width();
+    }
+
     switch (this->getScanlineOrder()) {
         case kTopDown_SkScanlineOrder:
         case kNone_SkScanlineOrder: {
-            const SkImageInfo fillInfo = info.makeWH(info.width(), linesRemaining);
+            const SkImageInfo fillInfo = info.makeWH(fillWidth, linesRemaining);
             fillDst = SkTAddOffset<void>(dst, linesDecoded * rowBytes);
             fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
             break;
         }
         case kBottomUp_SkScanlineOrder: {
             fillDst = dst;
-            const SkImageInfo fillInfo = info.makeWH(info.width(), linesRemaining);
+            const SkImageInfo fillInfo = info.makeWH(fillWidth, linesRemaining);
             fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
             break;
         }
         case kOutOfOrder_SkScanlineOrder: {
             SkASSERT(1 == linesRequested || this->getInfo().height() == linesRequested);
-            const SkImageInfo fillInfo = info.makeWH(info.width(), 1);
+            const SkImageInfo fillInfo = info.makeWH(fillWidth, 1);
             for (int srcY = linesDecoded; srcY < linesRequested; srcY++) {
                 fillDst = SkTAddOffset<void>(dst, this->outputScanline(srcY) * rowBytes);
                 fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
diff --git a/src/codec/SkJpegCodec.cpp b/src/codec/SkJpegCodec.cpp
index e1440af5c3..d36051511c 100644
--- a/src/codec/SkJpegCodec.cpp
+++ b/src/codec/SkJpegCodec.cpp
@@ -80,6 +80,7 @@ SkJpegCodec::SkJpegCodec(const SkImageInfo& srcInfo, SkStream* stream,
     : INHERITED(srcInfo, stream)
     , fDecoderMgr(decoderMgr)
     , fReadyState(decoderMgr->dinfo()->global_state)
+    , fSwizzlerSubset(SkIRect::MakeEmpty())
 {}
 
 /*
@@ -371,7 +372,16 @@ void SkJpegCodec::initializeSwizzler(const SkImageInfo& dstInfo, const Options&
         srcConfig = SkSwizzler::kRGB;
     }
 
-    fSwizzler.reset(SkSwizzler::CreateSwizzler(srcConfig, nullptr, dstInfo, options));
+    Options swizzlerOptions = options;
+    if (options.fSubset) {
+        // Use fSwizzlerSubset if this is a subset decode.  This is necessary in the case
+        // where libjpeg-turbo provides a subset and then we need to subset it further.
+        // Also, verify that fSwizzlerSubset is initialized and valid.
+        SkASSERT(!fSwizzlerSubset.isEmpty() && fSwizzlerSubset.x() <= options.fSubset->x() &&
+                fSwizzlerSubset.width() == options.fSubset->width());
+        swizzlerOptions.fSubset = &fSwizzlerSubset;
+    }
+    fSwizzler.reset(SkSwizzler::CreateSwizzler(srcConfig, nullptr, dstInfo, swizzlerOptions));
     SkASSERT(fSwizzler);
     fStorage.reset(get_row_bytes(fDecoderMgr->dinfo()));
     fSrcRow = fStorage.get();
@@ -411,12 +421,60 @@ SkCodec::Result SkJpegCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         return kInvalidInput;
     }
 
+    if (options.fSubset) {
+        fSwizzlerSubset = *options.fSubset;
+    }
+
+#ifdef TURBO_HAS_CROP
+    if (options.fSubset) {
+        uint32_t startX = options.fSubset->x();
+        uint32_t width = options.fSubset->width();
+
+        // libjpeg-turbo may need to align startX to a multiple of the IDCT
+        // block size.  If this is the case, it will decrease the value of
+        // startX to the appropriate alignment and also increase the value
+        // of width so that the right edge of the requested subset remains
+        // the same.
+        jpeg_crop_scanline(fDecoderMgr->dinfo(), &startX, &width);
+
+        SkASSERT(startX <= (uint32_t) options.fSubset->x());
+        SkASSERT(width >= (uint32_t) options.fSubset->width());
+        SkASSERT(startX + width >= (uint32_t) options.fSubset->right());
+
+        // Instruct the swizzler (if it is necessary) to further subset the
+        // output provided by libjpeg-turbo.
+        //
+        // We set this here (rather than in the if statement below), so that
+        // if (1) we don't need a swizzler for the subset, and (2) we need a
+        // swizzler for CMYK, the swizzler will still use the proper subset
+        // dimensions.
+        //
+        // Note that the swizzler will ignore the y and height parameters of
+        // the subset.  Since the scanline decoder (and the swizzler) handle
+        // one row at a time, only the subsetting in the x-dimension matters.
+        fSwizzlerSubset.setXYWH(options.fSubset->x() - startX, 0,
+                options.fSubset->width(), options.fSubset->height());
+
+        // We will need a swizzler if libjpeg-turbo cannot provide the exact
+        // subset that we request.
+        if (startX != (uint32_t) options.fSubset->x() ||
+                width != (uint32_t) options.fSubset->width()) {
+            this->initializeSwizzler(dstInfo, options);
+        }
+    }
+
+    // Make sure we have a swizzler if we are converting from CMYK.
+    if (!fSwizzler && JCS_CMYK == fDecoderMgr->dinfo()->out_color_space) {
+        this->initializeSwizzler(dstInfo, options);
+    }
+#else
     // We will need a swizzler if we are performing a subset decode or
     // converting from CMYK.
     J_COLOR_SPACE colorSpace = fDecoderMgr->dinfo()->out_color_space;
     if (options.fSubset || JCS_CMYK == colorSpace || JCS_RGB == colorSpace) {
         this->initializeSwizzler(dstInfo, options);
     }
+#endif
 
     return kSuccess;
 }
diff --git a/src/codec/SkJpegCodec.h b/src/codec/SkJpegCodec.h
index 06685cfd4c..bb5ce75375 100644
--- a/src/codec/SkJpegCodec.h
+++ b/src/codec/SkJpegCodec.h
@@ -115,6 +115,10 @@ private:
     // scanline decoding
     SkAutoTMalloc<uint8_t>     fStorage;    // Only used if sampling is needed
     uint8_t*                   fSrcRow;     // Only used if sampling is needed
+    // libjpeg-turbo provides some subsetting.  In the case that libjpeg-turbo
+    // cannot take the exact the subset that we need, we will use the swizzler
+    // to further subset the output from libjpeg-turbo.
+    SkIRect                    fSwizzlerSubset;
     SkAutoTDelete<SkSwizzler>  fSwizzler;
     
     typedef SkCodec INHERITED;