X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=overlay_effect.h;h=444fe3f67298c33acc0ec12c4287210802458c65;hp=06ff7939128257e9ccc006e3076b3e91b29aaeb5;hb=88ee2edc41d536c7057424df185fc6b49f993896;hpb=5e05605a85a15944b95d7000745446756cdcbfa8

diff --git a/overlay_effect.h b/overlay_effect.h
index 06ff793..444fe3f 100644
--- a/overlay_effect.h
+++ b/overlay_effect.h
@@ -1,15 +1,17 @@
-#ifndef _OVERLAY_EFFECT_H
-#define _OVERLAY_EFFECT_H 1
+#ifndef _MOVIT_OVERLAY_EFFECT_H
+#define _MOVIT_OVERLAY_EFFECT_H 1
 
 // Put one image on top of another, using alpha where appropriate.
 // (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)
+#endif // !defined(_MOVIT_OVERLAY_EFFECT_H)