1 files changed, 22 insertions, 1 deletions
diff --git a/servers/rendering/rasterizer_rd/shaders/tonemap.glsl b/servers/rendering/rasterizer_rd/shaders/tonemap.glsl
index 74449496f6..341cdab1ef 100644
--- a/servers/rendering/rasterizer_rd/shaders/tonemap.glsl
+++ b/servers/rendering/rasterizer_rd/shaders/tonemap.glsl
@@ -48,7 +48,7 @@ layout(push_constant, binding = 1, std430) uniform Params {
 
 	vec2 pixel_size;
 	bool use_fxaa;
-	uint pad;
+	bool use_debanding;
 }
 params;
 
@@ -157,6 +157,10 @@ vec3 tonemap_aces(vec3 color, float white) {
 }
 
 vec3 tonemap_reinhard(vec3 color, float white) {
+	// Ensure color values are positive.
+	// They can be negative in the case of negative lights, which leads to undesired behavior.
+	color = max(vec3(0.0), color);
+
 	return (white * color + color) / (color * white + white);
 }
 
@@ -301,6 +305,18 @@ vec3 do_fxaa(vec3 color, float exposure, vec2 uv_interp) {
 	}
 }
 
+// From http://alex.vlachos.com/graphics/Alex_Vlachos_Advanced_VR_Rendering_GDC2015.pdf
+// and https://www.shadertoy.com/view/MslGR8 (5th one starting from the bottom)
+// NOTE: `frag_coord` is in pixels (i.e. not normalized UV).
+vec3 screen_space_dither(vec2 frag_coord) {
+	// Iestyn's RGB dither (7 asm instructions) from Portal 2 X360, slightly modified for VR.
+	vec3 dither = vec3(dot(vec2(171.0, 231.0), frag_coord));
+	dither.rgb = fract(dither.rgb / vec3(103.0, 71.0, 97.0));
+
+	// Subtract 0.5 to avoid slightly brightening the whole viewport.
+	return (dither.rgb - 0.5) / 255.0;
+}
+
 void main() {
 	vec3 color = textureLod(source_color, uv_interp, 0.0f).rgb;
 
@@ -324,6 +340,11 @@ void main() {
 	if (params.use_fxaa) {
 		color = do_fxaa(color, exposure, uv_interp);
 	}
+	if (params.use_debanding) {
+		// For best results, debanding should be done before tonemapping.
+		// Otherwise, we're adding noise to an already-quantized image.
+		color += screen_space_dither(gl_FragCoord.xy);
+	}
 	color = apply_tonemapping(color, params.white);
 
 	color = linear_to_srgb(color); // regular linear -> SRGB conversion