Prototype of RAW decoding in Skia.

src/codec/SkCodec.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 "SkBmpCodec.h"
 #include "SkCodec.h"
 #include "SkData.h"
 #include "SkCodec_libgif.h"
 #include "SkCodec_libico.h"
 #include "SkCodec_libpng.h"
 #include "SkCodec_wbmp.h"
 #include "SkCodecPriv.h"
 #if !defined(GOOGLE3)
 #include "SkJpegCodec.h"
 #endif
+#ifdef SK_CODEC_DECODES_RAW
+#include "SkRawCodec.h"
+#endif
 #include "SkStream.h"
 #include "SkWebpCodec.h"
 
 struct DecoderProc {
     bool (*IsFormat)(const void*, size_t);
     SkCodec* (*NewFromStream)(SkStream*);
 };
 
 static const DecoderProc gDecoderProcs[] = {
 #if !defined(GOOGLE3)
@@ skipping 49 matching lines @@
     // But this code follows the same pattern as the loop.
     if (SkPngCodec::IsPng(buffer, bytesRead)) {
         codec.reset(SkPngCodec::NewFromStream(streamDeleter.detach(), chunkReader));
     } else {
         for (DecoderProc proc : gDecoderProcs) {
             if (proc.IsFormat(buffer, bytesRead)) {
                 codec.reset(proc.NewFromStream(streamDeleter.detach()));
                 break;
             }
         }
+
+        // Try to treat the input as RAW if all the other checks failed.
+        if (!codec && streamDeleter) {

[msarett, 2016/01/07 16:39:11]

We check streamDeleter here because one of the other codecs may take ownership,
fail to create a codec (return NULL), and then delete the stream?

I think this is correct, just want to make sure I understand.

[scroggo, 2016/01/07 20:57:42]

I think this is redundant.

If codec is NULL, streamDeleter should not be NULL. Maybe this should
SkASSERT(streamDeleter) instead?

[yujieqin, 2016/01/08 14:00:12]

msarett@, yes, we run into once this issue that other codec.NewFromStream()
already took the ownership but failed to create the codec. In this case, the
(codec == nullptr) and (streamDeleter == nullptr).

scroggo@, do you think the case mentioned above is actually an assert? Just
asking because I think the current skia does not treat this case as an
assertion.

[scroggo, 2016/01/08 17:12:25]

My mistake. It is possible that the first few bytes told us it was a BMP (for
example), so we try to create a BMP codec. But the stream fails shortly
thereafter. BMP still deletes the stream (since we don't need to check if it's
something else), so both are NULL.

But I think you can make it the other way around:

if (streamDeleter) {
    SkASSERT(!codec);
    codec.reset(...);
}

If there is still a stream, to use, there should not be a codec already created.
If there was, we should already have a problem of use after free (streamDeleter
deletes it before codec keeps reading it).

+#ifdef SK_CODEC_DECODES_RAW

[msarett, 2016/01/07 16:39:11]

nit: Can we surround the entire if statement with the #ifdef?

[yujieqin, 2016/01/08 14:00:12]

Done.

+            codec.reset(SkRawCodec::NewFromStream(streamDeleter.detach()));
+#endif
+        }
     }
 
     // Set the max size at 128 megapixels (512 MB for kN32).
     // This is about 4x smaller than a test image that takes a few minutes for
     // dm to decode and draw.
     const int32_t maxSize = 1 << 27;
     if (codec && codec->getInfo().width() * codec->getInfo().height() > maxSize) {
         SkCodecPrintf("Error: Image size too large, cannot decode.\n");
         return nullptr;
     } else {
@@ skipping 276 matching lines @@
             SkASSERT(1 == linesRequested || this->getInfo().height() == linesRequested);
             const SkImageInfo fillInfo = info.makeWH(info.width(), 1);
             for (int srcY = linesDecoded; srcY < linesRequested; srcY++) {
                 fillDst = SkTAddOffset<void>(dst, this->outputScanline(srcY) * rowBytes);
                 fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
             }
             break;
         }
     }
 }