From 6dbc310df4aa2ad24cef47781c07f0818fca465b Mon Sep 17 00:00:00 2001
From: outfoxxed <outfoxxed@outfoxxed.me>
Date: Sat, 17 May 2025 17:03:03 -0700
Subject: [PATCH] widgets/cliprect: fix premultiplied alpha blending

---
 src/widgets/shaders/cliprect.frag | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/widgets/shaders/cliprect.frag b/src/widgets/shaders/cliprect.frag
index f1c004a1..2b8db2a8 100644
--- a/src/widgets/shaders/cliprect.frag
+++ b/src/widgets/shaders/cliprect.frag
@@ -14,11 +14,12 @@ layout(binding = 2) uniform sampler2D content;
 
 vec4 overlay(vec4 base, vec4 overlay) {
 	if (overlay.a == 0.0) return base;
+	if (base.a == 0.0) return overlay;
 
-	float baseMul = 1.0 - overlay.a;
-	float newAlpha = overlay.a + base.a * baseMul;
-	vec3 rgb = (overlay.rgb * overlay.a + base.rgb * base.a * baseMul) / newAlpha;
-	return vec4(rgb, newAlpha);
+	vec3 rgb = overlay.rgb + base.rgb * (1.0 - overlay.a);
+	float a = overlay.a + base.a * (1.0 - overlay.a);
+
+	return vec4(rgb, a);
 }
 
 void main() {