X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=overlay_effect.h;h=66ff31b94be55d19ffacb7714051baa2c785493c;hp=06ff7939128257e9ccc006e3076b3e91b29aaeb5;hb=ad66f9714e4a36008c341355700272a52484a785;hpb=5e05605a85a15944b95d7000745446756cdcbfa8

diff --git a/overlay_effect.h b/overlay_effect.h
index 06ff793..66ff31b 100644
--- a/overlay_effect.h
+++ b/overlay_effect.h
@@ -5,11 +5,13 @@
 // (If both images are the same aspect and the top image has alpha=1.0
 // for all pixels, you will not see anything of the one on the bottom.)
 //
-// This is the “atop” operation from Porter-Duff blending, also used
+// This is the “over” operation from Porter-Duff blending, also used
 // when merging layers in e.g. GIMP or Photoshop.
 //
 // The first input is the bottom, and the second is the top.
 
+#include <string>
+
 #include "effect.h"
 
 class OverlayEffect : public Effect {
@@ -20,6 +22,13 @@ public:
 
 	virtual bool needs_srgb_primaries() const { return false; }
 	virtual unsigned num_inputs() const { return 2; }
+
+	// Actually, if _either_ image has blank alpha, our output will have
+	// blank alpha, too (this only tells the framework that having _both_
+	// images with blank alpha would result in blank alpha).
+	// However, understanding that would require changes
+	// to EffectChain, so postpone that optimization for later.
+	virtual AlphaHandling alpha_handling() const { return INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK; }
 };
 
 #endif // !defined(_OVERLAY_EFFECT_H)