Support for libpng > 1.2.

Support for libpng > 1.2.

  * Add conditional defines for deprecated NULL type casts.
  * Use wrapper functions for accessing png_structp & png_infop fields
    (direct access is deprecated).

Tested on Fedora 17 (libpng 1.5) and Ubuntu 12.04 (libpng 1.2).

Note: there is one png_structp direct field acces left in
SkPNGImageDecoder::onDecodeRegion() for which libpng does not provide a
wrapper method (png_ptr->pass = 0). That should be OK for now as the code
is only enabled when SK_BUILD_FOR_ANDROID is set, and the Android libpng
version is striclty controlled. But it may become an issue in the future
when/if Android decides to update libpng, so we should investigate a
solution.


R=scroggo@google.com

Committed: http://code.google.com/p/skia/source/detail?r=8956

[scroggo, 2013-05-01 16:09:52]

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
File src/images/SkImageDecoder_libpng.cpp (right):

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
src/images/SkImageDecoder_libpng.cpp:260:
png_set_expand_gray_1_2_4_to_8(png_ptr);
Recently Derek upstreamed changes from Android that changed this from
png_set_expand_gray to png_set_gray.

Derek, do you know why they made this change?

It appears that png_set_gray is an alias?

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
src/images/SkImageDecoder_libpng.cpp:730: // and no wrapper method is provided
for resetting the interlace pass.
Would it be possible to check the PNG version here?

[fmalita_google_do_not_use, 2013-05-01 16:20:44]

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
File src/images/SkImageDecoder_libpng.cpp (right):

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
src/images/SkImageDecoder_libpng.cpp:260:
png_set_expand_gray_1_2_4_to_8(png_ptr);
On 2013/05/01 16:09:53, scroggo wrote:
> It appears that png_set_gray is an alias?
Right, it's a deprecated alias (marked as such in libpng 1.2 and completely
removed in later versions):

#if defined(PNG_1_0_X) || defined (PNG_1_2_X)
/* Deprecated */
extern PNG_EXPORT(void,png_set_gray_1_2_4_to_8) PNGARG((png_structp
    png_ptr)) PNG_DEPRECATED;
#endif

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
src/images/SkImageDecoder_libpng.cpp:730: // and no wrapper method is provided
for resetting the interlace pass.
On 2013/05/01 16:09:53, scroggo wrote:
> Would it be possible to check the PNG version here?

Sure, but then I wonder what (if anything) will break for Android + libpng >
1.2. I don't really understand why we're resetting the pass here - can it be
avoided altogether?

[scroggo, 2013-05-01 17:35:03]

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
File src/images/SkImageDecoder_libpng.cpp (right):

https://codereview.chromium.org/14645018/diff/1/src/images/SkImageDecoder_lib...
src/images/SkImageDecoder_libpng.cpp:730: // and no wrapper method is provided
for resetting the interlace pass.
On 2013/05/01 16:20:44, fmalita wrote:
> On 2013/05/01 16:09:53, scroggo wrote:
> > Would it be possible to check the PNG version here?
> 
> Sure, but then I wonder what (if anything) will break for Android + libpng >
> 1.2. I don't really understand why we're resetting the pass here - can it be
> avoided altogether?

Good question. I'm guessing this is for consecutive calls to onDecodeRegion,
which may have left pass set to a higher value? The line appears to have been
inserted into code that was otherwise taken from example.c

[scroggo, 2013-05-02 00:01:00]

lgtm

[commit-bot: I haz the power, 2013-05-02 13:33:19]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/fmalita@google.com/14645018/11001

[commit-bot: I haz the power, 2013-05-02 13:41:37]

Change committed as 8956

[scroggo, 2013-05-02 15:06:37]

https://chromiumcodereview.appspot.com/14645018/diff/11001/src/images/SkImage...
File src/images/SkImageDecoder_libpng.cpp (right):

https://chromiumcodereview.appspot.com/14645018/diff/11001/src/images/SkImage...
src/images/SkImageDecoder_libpng.cpp:732: png_ptr->pass = 0;
There is a function call png_set_interlaced_pass, which sets png_ptr->pass. It
also sets png_ptr->iwidth, which is probably the correct thing to do, but I'm
not sure yet.