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575b138d0c
In general, the component alpha version of an operator is supposed to
do this:
- multiply source with mask in all channels
- multiply mask with source alpha in all channels
- compute the regular operator in all channels using the
mask value whenever source alpha is called for
The first two steps are usually accomplished with the function
combine_mask_ca(), but for operators where source alpha is not used,
such as SRC, ADD and OUT, the simpler function
combine_mask_value_ca(), which doesn't compute the new mask values,
can be used.
However, the PDF blend modes generally *do* make use of source alpha,
so they can't use combine_mask_value_ca() as they do now. They have to
use combine_mask_ca().
This patch fixes this in combine_multiply_ca() and the CA combiners
generated by PDF_SEPARABLE_BLEND_MODE.