wimmel.frag: Discard fragment early if difference is to significant

1 files changed, 6 insertions, 3 deletions

diff --git a/wimmel.frag b/wimmel.frag
index d3cf745..b9271d7 100644
--- a/wimmel.frag
+++ b/wimmel.frag
@@ -12,16 +12,19 @@ main()
 	float height = search_rect[3];
 	int diff = 0;
 
-	for (i = 0.0; i < width && diff < barrier; i += pixelsize.x) {
-		for (j = 0.0; j < height && diff < barrier; j += pixelsize.y) {
+	for (i = 0.0; i < width; i += pixelsize.x) {
+		for (j = 0.0; j < height; j += pixelsize.y) {
 			vec4 match = texture2D(tex, search_rect.xy + vec2(i,j));
 			vec4 orig = texture2D(tex, v_texcoord + vec2(i,j));
 
 			diff += int(any(greaterThan(abs(orig - match), vec4(0.2))));
+			if (diff >= barrier)
+				discard;
 		}
 	}
 
-	gl_FragColor = vec4(float(diff < barrier), 0.0, 0.0, 1.0);
+	/* Only written if fragment is NOT discarded in loop */
+	gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
 }
 
 // vim:ft=c: