Use preprocessor to select the yuv color matrix in ps_yuv_image shader.

webrender/res/ps_yuv_image.fs.glsl

@@ -3,6 +3,33 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+// The constants added to the Y, U and V components are applied in the fragment shader.
+#if defined(WR_FEATURE_YUV_REC601)
+// From Rec601:
+// [R]   [1.1643835616438356,  0.0,                 1.5960267857142858   ]   [Y -  16]
+// [G] = [1.1643835616438358, -0.3917622900949137, -0.8129676472377708   ] x [U - 128]
+// [B]   [1.1643835616438356,  2.017232142857143,   8.862867620416422e-17]   [V - 128]
+//
+// For the range [0,1] instead of [0,255].
+const mat3 YuvColorMatrix = mat3(
+    1.16438,  0.0,      1.59603,
+    1.16438, -0.39176, -0.81297,
+    1.16438,  2.01723,  0.0
+);
+#elif defined(WR_FEATURE_YUV_REC709)
+// From Rec709:
+// [R]   [1.1643835616438356,  4.2781193979771426e-17, 1.7927410714285714]   [Y -  16]
+// [G] = [1.1643835616438358, -0.21324861427372963,   -0.532909328559444 ] x [U - 128]
+// [B]   [1.1643835616438356,  2.1124017857142854,     0.0               ]   [V - 128]
+//
+// For the range [0,1] instead of [0,255]:
+const mat3 YuvColorMatrix = mat3(
+    1.16438,  0.0,      1.79274,
+    1.16438, -0.21325, -0.53291,
+    1.16438,  2.11240,  0.0
+);
+#endif
+
 void main(void) {
 #ifdef WR_FEATURE_TRANSFORM
     float alpha = 0.0;
@@ -33,7 +60,7 @@ void main(void) {
     float u = textureLod(sColor1, st_u, 0.0).r;
     float v = textureLod(sColor2, st_v, 0.0).r;
 
-    // See the vertex shader for an explanation of where the constants come from.
-    vec3 rgb = vYuvColorMatrix * vec3(y - 0.06275, u - 0.50196, v - 0.50196);
+    // See the YuvColorMatrix definition for an explanation of where the constants come from.
+    vec3 rgb = YuvColorMatrix * vec3(yuv_value.x - 0.06275, yuv_value.y - 0.50196, yuv_value.z - 0.50196);
     oFragColor = vec4(rgb, alpha);
 }

webrender/res/ps_yuv_image.glsl

@@ -11,8 +11,6 @@ flat varying vec2 vStretchSize;
 flat varying vec2 vHalfTexelY;     // Normalized length of the half of a Y texel.
 flat varying vec2 vHalfTexelUv;    // Normalized length of the half of u and v texels.
 
-flat varying mat3 vYuvColorMatrix;
-
 #ifdef WR_FEATURE_TRANSFORM
 varying vec3 vLocalPos;
 flat varying RectWithSize vLocalRect;

webrender/res/ps_yuv_image.vs.glsl

@@ -53,32 +53,6 @@ void main(void) {
     vHalfTexelY = vec2(0.5) / y_texture_size;
     vHalfTexelUv = vec2(0.5) / uv_texture_size;
 
-    // The constants added to the Y, U and V components are applied in the fragment shader.
-    if (image.color_space == YUV_REC601) {
-        // From Rec601:
-        // [R]   [1.1643835616438356,  0.0,                 1.5960267857142858   ]   [Y -  16]
-        // [G] = [1.1643835616438358, -0.3917622900949137, -0.8129676472377708   ] x [U - 128]
-        // [B]   [1.1643835616438356,  2.017232142857143,   8.862867620416422e-17]   [V - 128]
-        //
-        // For the range [0,1] instead of [0,255].
-        vYuvColorMatrix = mat3(
-            1.16438,  0.0,      1.59603,
-            1.16438, -0.39176, -0.81297,
-            1.16438,  2.01723,  0.0
-        );
-    } else { // if (image.color_space == YUV_REC709)
-        // From Rec709:
-        // [R]   [1.1643835616438356,  4.2781193979771426e-17, 1.7927410714285714]   [Y -  16]
-        // [G] = [1.1643835616438358, -0.21324861427372963,   -0.532909328559444 ] x [U - 128]
-        // [B]   [1.1643835616438356,  2.1124017857142854,     0.0               ]   [V - 128]
-        //
-        // For the range [0,1] instead of [0,255]:
-        vYuvColorMatrix = mat3(
-            1.16438,  0.0,      1.79274,
-            1.16438, -0.21325, -0.53291,
-            1.16438,  2.11240,  0.0
-        );
-    }
 
     write_clip(vi.screen_pos, prim.clip_area);