X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=overlay_effect.h;h=64224afe572b9a7e738af3ab0a72fe8bb61a15ea;hp=06ff7939128257e9ccc006e3076b3e91b29aaeb5;hb=ad27ef8410ceeabbadd57ace746867f04337844b;hpb=5e05605a85a15944b95d7000745446756cdcbfa8

diff --git a/overlay_effect.h b/overlay_effect.h
index 06ff793..64224af 100644
--- a/overlay_effect.h
+++ b/overlay_effect.h
@@ -5,7 +5,7 @@
 // (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.
@@ -20,6 +20,11 @@ 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. However, understanding that would require changes
+	// to EffectChain, so postpone that optimization for later.
+	virtual AlphaHandling alpha_handling() const { return INPUT_AND_OUTPUT_ALPHA_PREMULTIPLIED; }
 };
 
 #endif // !defined(_OVERLAY_EFFECT_H)