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Change option (SUPPORTED) names, dummy code

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The filter selection options are made more intuitive (IMO, but I am not an
Intuitive User).  Dummy code added for methodical filter selection.

Signed-off-by: John Bowler <jbowler@acm.org>
This commit is contained in:
John Bowler
2015-12-02 19:03:28 -08:00
parent 71c5123a4d
commit 9fce04fcd6
5 changed files with 102 additions and 61 deletions
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38
png.h
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@@ -1661,22 +1661,26 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
* ignored if SUB is set; this is because these filter pairs are equivalent
* when there is no previous row.
*
* PNG_WRITE_OPTIMIZE_FITLER_SUPPORTED:
* 2) If WRITE_OPTIMIZE_FILTER is supported and it has not been disabled by
* png_set_option(PNG_DISABLE_OPTIMIZE_FILTER, PNG_OPTION_ON) libpng tries
* all the filters in the list and selects the one which gives the shortest
* compressed row, favoring earlier filters.
* 2) PNG_SELECT_FILTER_METHODICALLY_SUPPORTED:
* If SELECT_FILTER_METHODICALLY is 'on' libpng tries all the filters in the
* list and selects the one which gives the shortest compressed row, favoring
* earlier filters.
*
* PNG_WRITE_HEURISTIC_FITLER_SUPPORTED:
* 3) If not (2) an WRITE_HEURISTIC_FILTER is supported and has not been
* disabled by png_set_option(PNG_DISABLE_HEURISTIC_FILTER, PNG_OPTION_ON)
* libpng tests the start of each row (a few thousand bytes at most) to see
* which filter is likely to produce best compression.
* 3) PNG_SELECT_FILTER_HEURISTICALLY_SUPPORTED:
* If SELECT_FILTER_HEURISTICALLY is 'on' libpng tests the start of each row
* (a few thousand bytes at most) to see which filter is likely to produce
* best compression.
*
* 4) If neither (2) nor (3) libpng selects the first filter in the list (there
* is no warning that this will happen - check the #defines if you need to
* know.)
*
* The seletion options are turned 'on' using png_set_option(method,
* PNG_OPTION_ON) and turned off with PNG_OPTION_OFF. If a selection method is
* turned off it will never be used, if neither option is turned on or off (i.e.
* if png_set_option is not called) the first supported option (2) or (3) will
* be used.
*
* If you intend to use 'previous row' filters in an image set either the UP or
* PAETH filter before the first call to png_write_row, depending on whether you
* want to use NONE or SUB on the first row.
@@ -1685,11 +1689,11 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
* preceding byte as a predictor and is not likely to have very good
* performance.
*
* The WRITE_OPTIMIZE_FILTER option is slow and memory intensive, but it is
* likely to produce the smallest PNG file. Depending on the image data the
* HEURISTIC option may improve results and has little overall effect on
* compression speed, however it can sometimes produce larger files than not
* using any filtering.
* The SELECT_FILTER_METHODICALLY option is slow and memory intensive, but it is
* almost certain to produce the smallest PNG file. Depending on the image data
* the HEURISTIC option may improve results significantly over the NONE filter
* and it has little overall effect on compression speed, however it can
* sometimes produce larger files than not using any filtering.
*/
PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
int filters));
@@ -3491,8 +3495,8 @@ PNG_EXPORT(240, int, png_image_write_to_stdio, (png_imagep image, FILE *file,
#define PNG_EXTENSIONS 0 /* BOTH: enable or disable extensions */
#define PNG_MAXIMUM_INFLATE_WINDOW 2 /* SOFTWARE: force maximum window */
#define PNG_SKIP_sRGB_CHECK_PROFILE 4 /* SOFTWARE: Check ICC profile for sRGB */
#define PNG_DISABLE_HEURISTIC_FILTER 6 /* SOFTWARE: see png_set_filter */
#define PNG_DISABLE_OPTIMIZE_FILTER 8 /* SOFTWARE: see png_set_filter */
#define PNG_SELECT_FILTER_HEURISTICALLY 6 /* SOFTWARE: see png_set_filter */
#define PNG_SELECT_FILTER_METHODICALLY 8 /* SOFTWARE: see png_set_filter */
#define PNG_OPTION_NEXT 10 /* Next option - numbers must be even */
/* Return values: NOTE: there are four values and 'off' is *not* zero */