Implement GPU-side dither

Summary:
Uses some magic pseudo-random which is actually a
texture coordinate hashing function.

TODOs:
- Dither noise is the same for all the frames.
- It's different from Floyd's dither we've been
  using before.
- Currently CPU and GPU dithering used different
  implementation. Ideally we need to use the same
  dither in CPU.

Reviewers: brecht

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D58

1 files changed, 39 insertions, 1 deletions

diff --git a/intern/opencolorio/gpu_shader_display_transform.glsl b/intern/opencolorio/gpu_shader_display_transform.glsl
index 6ba3fa55e8f..8a85d6cbffe 100644
--- a/intern/opencolorio/gpu_shader_display_transform.glsl
+++ b/intern/opencolorio/gpu_shader_display_transform.glsl
@@ -2,6 +2,10 @@ uniform sampler2D image_texture;
 uniform sampler3D lut3d_texture;
 uniform bool predivide;
 
+#ifdef USE_DITHER
+uniform float dither;
+#endif
+
 #ifdef USE_CURVE_MAPPING
 /* Curve mapping parameters
  *
@@ -102,6 +106,33 @@ vec4 curvemapping_evaluate_premulRGBF(vec4 col)
 }
 #endif
 
+#ifdef USE_DITHER
+float dither_random_value(vec2 co)
+{
+	return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453) * 0.005 * dither;
+}
+
+vec2 round_to_pixel(vec2 st)
+{
+	vec2 result;
+	vec2 size = textureSize(image_texture, 0);
+	result.x = float(int(st.x * size.x)) / size.x;
+	result.y = float(int(st.y * size.y)) / size.y;
+	return result;
+}
+
+vec4 apply_dither(vec2 st, vec4 col)
+{
+	vec4 result;
+	float random_value = dither_random_value(round_to_pixel(st));
+	result.r = col.r + random_value;
+	result.g = col.g + random_value;
+	result.b = col.b + random_value;
+	result.a = col.a;
+	return result;
+}
+#endif
+
 void main()
 {
 	vec4 col = texture2D(image_texture, gl_TexCoord[0].st);
@@ -119,5 +150,12 @@ void main()
 	 *       and the reason is simple -- opengl is always configured
 	 *       for straight alpha at this moment
 	 */
-	gl_FragColor = OCIODisplay(col, lut3d_texture);
+
+	vec4 result = OCIODisplay(col, lut3d_texture);
+
+#ifdef USE_DITHER
+	result = apply_dither(gl_TexCoord[0].st, result);
+#endif
+
+	gl_FragColor = result;
 }