ffmpegdecoder: use real colorspace coefficients in shader

app/shaders/yuv2rgb.frag

@@ -3,39 +3,59 @@ uniform sampler2D u_channel;
 uniform sampler2D v_channel;
 
 uniform int bits_per_pixel;
-uniform bool jpeg_range;
+uniform bool full_range;
+
+uniform int yuv_crv;
+uniform int yuv_cgu;
+uniform int yuv_cgv;
+uniform int yuv_cbu;
 
 in vec2 ove_texcoord;
 out vec4 frag_color;
 
-void main() {
-  vec4 rgba;
-
+void main()
+{
+  // Sample YUV planes
   vec3 yuv;
-
   yuv.r = texture(y_channel, ove_texcoord).r;
   yuv.g = texture(u_channel, ove_texcoord).r;
   yuv.b = texture(v_channel, ove_texcoord).r;
 
+  // Pixels will have come in aligned to 16-bit regardless of their actual bit depth, so they must
+  // be scaled as if they were actually 16-bit
   if (bits_per_pixel == 10) {
     yuv *= 64.0;
   } else if (bits_per_pixel == 12) {
     yuv *= 16.0;
   }
 
-  yuv.r = 1.1643 * (yuv.r - 0.0625);
+  // Convert YUV limited range from 16-235 to 0-255
+  yuv.r -= 0.0625; // 16/256
+  yuv.r *= 1.1643; // 255/219
+
+  // Convert 0.0-1.0 to -0.5-0.5
   yuv.g = yuv.g - 0.5;
   yuv.b = yuv.b - 0.5;
 
-  rgba.r = yuv.r + 1.5958 * yuv.b;
-  rgba.g = yuv.r - 0.39173 * yuv.g - 0.81290 * yuv.b;
-  rgba.b = yuv.r + 2.017 * yuv.g;
-  rgba.a = 1.0;
+  // Use coefficients to weigh YUV into RGB
+  float crv = float(yuv_crv) / 65536.0;
+  float cgu = float(yuv_cgu) / 65536.0;
+  float cgv = float(yuv_cgv) / 65536.0;
+  float cbu = float(yuv_cbu) / 65536.0;
 
-  if (jpeg_range) {
-    rgba.rgb *= 219.0 / 255.0;
-    rgba.rgb += 16.0 / 255.0;
+  vec4 rgba;
+  rgba.r = yuv.r + crv * yuv.b;
+  rgba.g = yuv.r - cgu * yuv.g - cgv * yuv.b;
+  rgba.b = yuv.r + cbu * yuv.g;
+
+  // If the expected value is full range, transform to full range here
+  if (full_range) {
+    rgba.rgb /= 1.1643;
+    rgba.rgb += 0.0625;
   }
 
+  // Currently this shader is only used for RGB textures, so just set alpha to 1
+  rgba.a = 1.0;
+
   frag_color = rgba;
 }