/usr/share/movit/overlay_effect.frag is in libmovit8 1.6.1-1.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | // It's actually (but surprisingly) not correct to do a mix() here;
// it would be if we had postmultiplied alpha and didn't have to worry
// about alpha in the bottom layer, but given that we use premultiplied
// alpha all over, top shouldn't actually be multiplied by anything.
//
// These formulas come from Wikipedia:
//
// http://en.wikipedia.org/wiki/Alpha_compositing
//
// We use the associative version given. However, note that since we want
// _output_ to be premultiplied, C_o from Wikipedia is not what we want,
// but rather c_o (which is not explicitly given, but obviously is just
// C_o without the division by alpha_o).
vec4 FUNCNAME(vec2 tc) {
// SWAP_INPUTS will be #defined to 1 if we want to swap the two inputs,
#if SWAP_INPUTS
vec4 bottom = INPUT2(tc);
vec4 top = INPUT1(tc);
#else
vec4 bottom = INPUT1(tc);
vec4 top = INPUT2(tc);
#endif
return top + (1.0 - top.a) * bottom;
}
#undef SWAP_INPUTS
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