Merge pull request #39 from emilianavt/master

Implement correctly blended premultiplied alpha
Off-World-Live · Apr 6, 2022 · 51c8411 · 51c8411
2 parents f49b0e4 + 9e238a6
commit 51c8411
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Showing 2 changed files with 17 additions and 2 deletions.
diff --git a/data/locale/en-US.ini b/data/locale/en-US.ini
@@ -5,8 +5,9 @@ spoutsenders="Spout Senders"
 sourcename="Spout2 Capture"
 compositemode="Composite mode"
 compositemodeopaque="Opaque"
-compositemodealpha="Premultiplied Alpha"
+compositemodealpha="Converted Premultiplied Alpha (legacy)"
 compositemodedefault="Default"
+compositemodepremultiplied="Premultiplied Alpha"
 tickspeedlimit="Poll time for new senders"
 tickspeedcrazy="crazy"
 tickspeedfast="fast"

diff --git a/source/win-spout-source.cpp b/source/win-spout-source.cpp
@@ -31,6 +31,7 @@
 #define COMPOSITE_MODE_OPAQUE 1
 #define COMPOSITE_MODE_ALPHA 2
 #define COMPOSITE_MODE_DEFAULT 3
+#define COMPOSITE_MODE_PREMULTIPLIED 4
 
 struct spout_source {
 	obs_source_t *source;
@@ -302,7 +303,13 @@ static void win_spout_source_render(void *data, gs_effect_t *effect)
 		effect = obs_get_base_effect(OBS_EFFECT_OPAQUE);
 		break;
 	case COMPOSITE_MODE_ALPHA:
-		effect = obs_get_base_effect(OBS_EFFECT_PREMULTIPLIED_ALPHA);
+		effect = obs_get_base_effect(OBS_EFFECT_PREMULTIPLIED_ALPHA); // Converts premultiplied to regular alpha before blending it as regular transparency.
+		break;
+	case COMPOSITE_MODE_PREMULTIPLIED:
+		effect = obs_get_base_effect(OBS_EFFECT_DEFAULT);
+		// Proper blending of premultiplied alpha needs a modified blend function and then works with the default blending effect.
+		gs_blend_state_push();
+		gs_blend_function(GS_BLEND_ONE, GS_BLEND_INVSRCALPHA);
 		break;
 	case COMPOSITE_MODE_DEFAULT:
 		effect = obs_get_base_effect(OBS_EFFECT_DEFAULT);
@@ -315,6 +322,10 @@ static void win_spout_source_render(void *data, gs_effect_t *effect)
 	while (gs_effect_loop(effect, "Draw")) {
 		obs_source_draw(context->texture, 0, 0, 0, 0, false);
 	}
+
+	if (context->composite_mode == COMPOSITE_MODE_PREMULTIPLIED) {
+		gs_blend_state_pop();
+	}
 }
 
 /**
@@ -416,6 +427,9 @@ static obs_properties_t *win_spout_properties(void *data)
 	obs_property_list_add_int(composite_mode_list,
 				  obs_module_text("compositemodedefault"),
 				  COMPOSITE_MODE_DEFAULT);
+	obs_property_list_add_int(composite_mode_list,
+				  obs_module_text("compositemodepremultiplied"),
+				  COMPOSITE_MODE_PREMULTIPLIED);
 
 	obs_property_t *tick_speed_limit_list = obs_properties_add_list(
 		props, SPOUT_TICK_SPEED_LIMIT,