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[libpng16] Better documentation of unknown handling API interactions.

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This commit is contained in:
John Bowler
2013-03-02 17:59:43 -06:00
committed by Glenn Randers-Pehrson
parent e57f094fd6
commit e15b537825
5 changed files with 41 additions and 16 deletions
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17
libpng.3
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@@ -1031,9 +1031,14 @@ you can retrieve with
png_get_user_chunk_ptr(png_ptr);
If you call the png_set_read_user_chunk_fn() function, then all unknown
chunks will be saved when read, in case your callback function will need
one or more of them. This behavior can be changed with the
png_set_keep_unknown_chunks() function, described below.
chunks which the callback does not handle will be saved when read. You can
cause them to be discarded by returning '1' ("handled") instead of '0'. This
behavior will change in libpng 1.7 and the default handling set by the
png_set_keep_unknown_chunks() function, described below, will be used when the
callback returns 0. If you want the existing behavior you should set the global
default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
At this point, you can set up a callback function that will be
called after each row has been read, which you can use to control
@@ -1132,8 +1137,10 @@ callback function:
...
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
/* ignore all unknown chunks: */
png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
/* ignore all unknown chunks
* (use global setting "2" for libpng16 and earlier):
*/
png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
/* except for vpAg: */
png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);