diff options
Diffstat (limited to 'converter/other/pngx.c')
| -rw-r--r-- | converter/other/pngx.c | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/converter/other/pngx.c b/converter/other/pngx.c index 4bb09421..7840b2da 100644 --- a/converter/other/pngx.c +++ b/converter/other/pngx.c @@ -24,7 +24,7 @@ errorHandler(png_structp const png_ptr, jmp_buf * jmpbufP; - /* this function, aside from the extra step of retrieving the "error + /* This function, aside from the extra step of retrieving the "error pointer" (below) and the fact that it exists within the application rather than within libpng, is essentially identical to libpng's default error handler. The second point is critical: since both @@ -416,6 +416,26 @@ void pngx_setFilter(struct pngx * const pngxP, int const filterSet) { + /* This sets the allowed filters in the compressor. The filters, and thus + the interpretation of 'filterSet', is specific to a filter method (aka + filter type), which you set with pngx_setIhdr. There is only one + filter method defined today, though (PNG_FILTER_TYPE_BASE). + + For filter method Base, 'filterSet' is the OR of the following masks, + each one allowing the compressor to use one filter. Not that the + compressor decides on a row-by-row basis what filter to use. + + PNG_FILTER_NONE + PNG_FILTER_SUB + PNG_FILTER_UP + PNG_FILTER_AVG + PNG_FILTER_PAETH + + There are also + + PNG_NO_FILTERS + PNG_ALL_FILTERS + */ png_set_filter(pngxP->png_ptr, 0, filterSet); } |