X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=dither_effect.frag;h=6994e8467f0c9645e47d9f74ff96700028eafddf;hp=9b39553099e314c940fb1401649517346910c6e1;hb=60e4852ff1b04c525a9e3f1c98a1017db28b27bd;hpb=ff9e68a3f5abb179bd7bf9fb84df48327f148583

diff --git a/dither_effect.frag b/dither_effect.frag
index 9b39553..6994e84 100644
--- a/dither_effect.frag
+++ b/dither_effect.frag
@@ -1,9 +1,21 @@
 uniform sampler2D PREFIX(dither_tex);
+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. We currently don't
-	// really handle alpha in any case.
-	return INPUT(tc) + texture2D(PREFIX(dither_tex), tc).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 += texture2D(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.
+#if NEED_EXPLICIT_ROUND
+	result = round(result * vec4(PREFIX(round_fac))) * vec4(PREFIX(inv_round_fac));
+#endif
+
+	return result;
 }