X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=dither_effect.frag;h=3b6b892d7606937867b4ab0c2b749926034d9f29;hp=f9c6ad13c443e1919c4506790159c9134106d8a7;hb=refs%2Fheads%2Fepoxy;hpb=271fa61d1251144b5558555ec9873e9f24a13a70

diff --git a/dither_effect.frag b/dither_effect.frag
index f9c6ad1..3b6b892 100644
--- a/dither_effect.frag
+++ b/dither_effect.frag
@@ -3,10 +3,13 @@ uniform vec2 PREFIX(tc_scale);
 uniform float PREFIX(round_fac), PREFIX(inv_round_fac);
 
 vec4 FUNCNAME(vec2 tc) {
-	// We also choose to dither alpha, just in case.
-	// Maybe it should in theory have a separate dither,
-	// but I doubt it matters much.
-	vec4 result = INPUT(tc) + texture2D(PREFIX(dither_tex), tc * PREFIX(tc_scale)).xxxx;
+	vec4 result = INPUT(tc);
+
+	// Don't dither alpha; the case of alpha=255 (1.0) is very important to us,
+	// and if there's any inaccuracy earlier in the chain so that it becomes e.g.
+	// 254.8, it's better to just get it rounded off than to dither and have it
+	// possibly get down to 254. This is not the case for the color components.
+	result.rgb += tex2D(PREFIX(dither_tex), tc * PREFIX(tc_scale)).xxx;
 
 	// NEED_EXPLICIT_ROUND will be #defined to 1 if the GPU has inaccurate
 	// fp32 -> int8 framebuffer rounding, and 0 otherwise.