1 #ifndef _OVERLAY_EFFECT_H
2 #define _OVERLAY_EFFECT_H 1
4 // Put one image on top of another, using alpha where appropriate.
5 // (If both images are the same aspect and the top image has alpha=1.0
6 // for all pixels, you will not see anything of the one on the bottom.)
8 // This is the “over” operation from Porter-Duff blending, also used
9 // when merging layers in e.g. GIMP or Photoshop.
11 // The first input is the bottom, and the second is the top.
15 class OverlayEffect : public Effect {
18 virtual std::string effect_type_id() const { return "OverlayEffect"; }
19 std::string output_fragment_shader();
21 virtual bool needs_srgb_primaries() const { return false; }
22 virtual unsigned num_inputs() const { return 2; }
24 // Actually, if either image has blank alpha, our output will have
25 // blank alpha, too. However, understanding that would require changes
26 // to EffectChain, so postpone that optimization for later.
27 virtual AlphaHandling alpha_handling() const { return INPUT_AND_OUTPUT_ALPHA_PREMULTIPLIED; }
30 #endif // !defined(_OVERLAY_EFFECT_H)