Add subsetting to SkScaledCodec

src/codec/SkJpegCodec.cpp

Index: src/codec/SkJpegCodec.cpp
diff --git a/src/codec/SkJpegCodec.cpp b/src/codec/SkJpegCodec.cpp
index 8c0a5b68931f791e4db2df54301a8739e46c650b..071b9753c23f4086fd1e0b14e34b1d89754ec633 100644
--- a/src/codec/SkJpegCodec.cpp
+++ b/src/codec/SkJpegCodec.cpp
@@ -163,19 +163,19 @@ SkISize SkJpegCodec::onGetScaledDimensions(float desiredScale) const {
     // support these as well
     long num;
     long denom = 8;
-    if (desiredScale > 0.875f) {
+    if (desiredScale >= 0.9375) {

[scroggo, 2015/10/02 18:27:03]

why did this change?

[msarett, 2015/10/06 23:01:27]

IMO, it used to make sense to always round up, since libjpeg-turbo also always
rounds up, we could be consistent in a sense.

Now we have completing scaling strategies, some of which round up and others of
which round down.  I think we should try to get as close as possible to the
requested scale, since we will be comparing this scaling option with other
scaling options, and choosing the best one.

         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;
@@ -368,7 +368,8 @@ SkCodec::Result SkJpegCodec::onGetPixels(const SkImageInfo& dstInfo,
     return kSuccess;
 }
 
-SkCodec::Result SkJpegCodec::initializeSwizzler(const SkImageInfo& info, const Options& options) {
+SkCodec::Result SkJpegCodec::initializeSwizzler(const SkImageInfo& info, const Options& options,
+        int subsetLeft, int subsetWidth) {
     SkSwizzler::SrcConfig srcConfig;
     switch (info.colorType()) {
         case kGray_8_SkColorType:
@@ -388,8 +389,8 @@ SkCodec::Result SkJpegCodec::initializeSwizzler(const SkImageInfo& info, const O
             SkASSERT(false);
     }
 
-    fSwizzler.reset(SkSwizzler::CreateSwizzler(srcConfig, nullptr, info, options.fZeroInitialized, 
-                                               this->getInfo()));
+    fSwizzler.reset(SkSwizzler::CreateSwizzler(srcConfig, nullptr, info, options.fZeroInitialized,
+                                               this->getInfo(), subsetLeft, subsetWidth));
     if (!fSwizzler) {
         return SkCodec::kUnimplemented;
     }
@@ -398,7 +399,8 @@ SkCodec::Result SkJpegCodec::initializeSwizzler(const SkImageInfo& info, const O
 }
 
 SkCodec::Result SkJpegCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
-        const Options& options, SkPMColor ctable[], int* ctableCount) {
+        const Options& options, SkPMColor ctable[], int* ctableCount, int subsetLeft,
+        int subsetWidth) {
     // Set the jump location for libjpeg errors
     if (setjmp(fDecoderMgr->getJmpBuf())) {
         SkCodecPrintf("setjmp: Error from libjpeg\n");
@@ -417,13 +419,29 @@ SkCodec::Result SkJpegCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         if (!SkScaledCodec::DimensionsSupportedForSampling(this->getInfo(), dstInfo)) {
             return kInvalidScale;
         }
+
         // create swizzler for sampling
-        Result result = this->initializeSwizzler(dstInfo, options);
-        if (kSuccess != result) {
+        SkCodec::Result result = this->initializeSwizzler(dstInfo, options, subsetLeft,
+                subsetWidth);
+        if (SkCodec::kSuccess != result) {
+            SkCodecPrintf("failed to initialize the swizzler.\n");
+            return result;
+        }
+        fStorage.reset(get_row_bytes(this->fDecoderMgr->dinfo()));
+        fSrcRow = static_cast<uint8_t*>(fStorage.get());
+    } else if (0 != subsetLeft || dstInfo.width() != subsetWidth) {
+        // TODO (msarett): If we implement a read partial scanlines API in libjpeg-turbo, we
+        //                 won't need to use the swizzler here.
+        // Create swizzler for subsetting.  We pass in the original info because scaling is
+        // handlded natively.
+        SkCodec::Result result = this->initializeSwizzler(
+                dstInfo.makeWH(this->getInfo().width(), this->getInfo().height()), options,
+                subsetLeft, subsetWidth);
+        if (SkCodec::kSuccess != result) {
             SkCodecPrintf("failed to initialize the swizzler.\n");
             return result;
         }
-        fStorage.reset(get_row_bytes(fDecoderMgr->dinfo()));
+        fStorage.reset(get_row_bytes(this->fDecoderMgr->dinfo()));
         fSrcRow = static_cast<uint8_t*>(fStorage.get());
     } else {
         fSrcRow = nullptr;