From 3aed5599c3f73cbfa53b0249795e76ab07cf9ecd Mon Sep 17 00:00:00 2001
From: Yuxuan Shui <yshuiv7@gmail.com>
Date: Mon, 8 May 2023 14:58:20 +0100
Subject: [PATCH] glx: calculate residual in both directions

We only considered residual in the positive direction, i.e. we would set
dithering to zero if the color is (whole number + 0.0001). But we should
also set dithering to zero if color is (whole number - 0.0001).

Fixes #1064
---
 src/backend/gl/shaders.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/backend/gl/shaders.c b/src/backend/gl/shaders.c
index 90f636b7..96e385b1 100644
--- a/src/backend/gl/shaders.c
+++ b/src/backend/gl/shaders.c
@@ -202,7 +202,8 @@ const char dither_glsl[] = GLSL(330,
 	}
 	vec4 dither(vec4 c, vec2 coord) {
 		vec4 residual = mod(c, 1.0 / 255.0);
-		vec4 dithered = vec4(greaterThan(residual, vec4(1e-4)));
+		residual = min(residual, vec4(1.0 / 255.0) - residual);
+		vec4 dithered = vec4(greaterThan(residual, vec4(1.0 / 65535.0)));
 		return vec4(c + dithered * bayer(coord) / 255.0);
 	}
 );