DPTLib > framebuf > composite
"composite" is a sub-library of DPTLib for performing Porter-Duff bitmap compositing.
The code is written to make use of degenerate cases where pixels are fully transparent or fully opaque.
Given input source src and destination dst bitmaps every pixel is composited according to the chosen rule and written back to dst.
The bitmaps given must have alpha channels: pixelfmt_rgba8888 and pixelfmt_bgra8888 formats are currently supported.
result_t composite(composite_rule_t rule,
const bitmap_t *src,
bitmap_t *dst);composite_RULE_CLEAR- [0, 0]
composite_RULE_SRC- [Sa, Sc]
composite_RULE_DST- [Da, Dc]
composite_RULE_SRC_OVER- [Sa + Da·(1 – Sa), Sc + Dc·(1 – Sa)]
composite_RULE_DST_OVER- [Da + Sa·(1 – Da), Dc + Sc·(1 – Da)]
composite_RULE_SRC_IN- [Sa·Da, Sc·Da]
composite_RULE_DST_IN- [Da·Sa, Dc·Sa]
composite_RULE_SRC_OUT- [Sa·(1 – Da), Sc·(1 – Da)]
composite_RULE_DST_OUT- [Da·(1 – Sa), Dc·(1 – Sa)]
composite_RULE_SRC_ATOP- [Da, Sc·Da + Dc·(1 – Sa)]
composite_RULE_DST_ATOP- [Sa, Dc·Sa + Sc·(1 – Da)]
composite_RULE_XOR- [Sa + Da – 2·Sa·Da, Sc·(1 – Da) + Dc·(1 – Sa)]
The 'destination out' rule can presently suffer with some distortions.