Fix T56992: OpenGL Render Engine ignores Transparent Background

Correct the outline blending for alpha 0 background.

1 files changed, 5 insertions, 1 deletions

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_deferred_composite_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_deferred_composite_frag.glsl
index bf856fbb212..a5e81526216 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_deferred_composite_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_deferred_composite_frag.glsl
@@ -44,7 +44,11 @@ void main()
 			fragColor = vec4(background, world_data.background_alpha);
 		}
 		else {
-			fragColor = vec4(mix(world_data.object_outline_color.rgb, background, object_outline), clamp(world_data.background_alpha, 1.0, object_outline));
+			/* Do correct alpha blending. */
+			vec4 background_color = vec4(background, 1.0);
+			vec4 outline_color = vec4(world_data.object_outline_color.rgb, 1.0) * world_data.background_alpha;
+			fragColor = mix(outline_color, background_color, object_outline);
+			fragColor = vec4(fragColor.rgb / max(1e-8, fragColor.a), fragColor.a);
 		}
 		return;
 	}