From 70f50ddc5e97020d64ea0702748a00eddebc2473 Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@nand.wakku.to>
Date: Wed, 26 Mar 2014 01:46:38 +0100
Subject: video: Add support for non-BT.709 primaries

This add support for reading primary information from lavc, categorized
into BT.601-525, BT.601-625, BT.709 and BT.2020; and passes it on to the
vo. In vo_opengl, we always generate the 3dlut against the wider BT.2020
and transform our source into this colorspace in the shader.
---
 video/out/gl_video_shaders.glsl | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

(limited to 'video/out/gl_video_shaders.glsl')

diff --git a/video/out/gl_video_shaders.glsl b/video/out/gl_video_shaders.glsl
index b0058f8ca6..a6ecc2eeeb 100644
--- a/video/out/gl_video_shaders.glsl
+++ b/video/out/gl_video_shaders.glsl
@@ -56,6 +56,13 @@ vec3 bt2020_expand(vec3 v)
 }
 #endif
 
+// Constant matrix for conversion from BT.2020 to sRGB
+const mat3 srgb_matrix = mat3(
+     1.6604910, -0.1245505, -0.0181508,
+    -0.5876411,  1.1328999, -0.1005789,
+    -0.0728499, -0.0083494,  1.1187297
+);
+
 #!section vertex_all
 
 #if __VERSION__ < 130
@@ -66,6 +73,7 @@ vec3 bt2020_expand(vec3 v)
 
 uniform mat3 transform;
 uniform sampler3D lut_3d;
+uniform mat3 cms_matrix; // transformation from file's gamut to bt.2020
 
 in vec2 vertex_position;
 in vec4 vertex_color;
@@ -89,12 +97,17 @@ void main() {
     // NOTE: This always applies the true BT2020, maybe we need to use
     // approx-gamma here too?
 #endif
+#ifdef USE_OSD_CMS_MATRIX
+    // Convert to the right target gamut first (to BT.709 for sRGB,
+    // and to BT.2020 for 3DLUT).
+    color.rgb = clamp(cms_matrix * color.rgb, 0, 1);
+#endif
 #ifdef USE_OSD_3DLUT
     color.rgb = pow(color.rgb, vec3(1/2.4)); // linear -> 2.4 3DLUT space
     color = vec4(texture3D(lut_3d, color.rgb).rgb, color.a);
 #endif
 #ifdef USE_OSD_SRGB
-    color.rgb = srgb_compand(color.rgb);
+    color.rgb = srgb_compand(clamp(srgb_matrix * color.rgb, 0, 1));
 #endif
 
     texcoord = vertex_texcoord;
@@ -136,6 +149,7 @@ uniform sampler2D lut_l_2d;
 uniform sampler3D lut_3d;
 uniform sampler2D dither;
 uniform mat4x3 colormatrix;
+uniform mat3 cms_matrix;
 uniform mat2 dither_trafo;
 uniform vec3 inv_gamma;
 uniform float input_gamma;
@@ -406,16 +420,28 @@ void main() {
     // User-defined gamma correction factor (via the gamma sub-option)
     color = pow(color, inv_gamma);
 #endif
+#ifdef USE_CMS_MATRIX
+    // Convert to the right target gamut first (to BT.709 for sRGB,
+    // and to BT.2020 for 3DLUT).
+    color = cms_matrix * color;
+#endif
 #ifdef USE_3DLUT
     // For the 3DLUT we are arbitrarily using 2.4 as input gamma to reduce
     // the amount of rounding errors, so we pull up to that space first and
     // then pass it through the 3D texture.
-    color = pow(color, vec3(1/2.4));
+    //
+    // The value is clamped to [0,1] first because the gamma function is not
+    // well-defined outside it. This should not be a problem because the 3dlut
+    // is not defined for values outside its boundaries either way, and no
+    // media can possibly exceed its BT.2020 source gamut either way due to
+    // that being the biggest taggable color space. This is just to avoid
+    // numerical quirks like -1e-30 turning into NaN.
+    color = pow(clamp(color, 0, 1), vec3(1/2.4));
     color = texture3D(lut_3d, color).rgb;
 #endif
 #ifdef USE_SRGB
-    // Compand from the linear scaling gamma to the sRGB output gamma
-    color = srgb_compand(color.rgb);
+    // Adapt and compand from the linear BT2020 source to the sRGB output
+    color = srgb_compand(clamp(srgb_matrix * color, 0, 1));
 #endif
 #ifdef USE_DITHER
     vec2 dither_pos = gl_FragCoord.xy / dither_size;
-- 
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