qcam: viewfinder_gl: Take color space into account for YUV rendering

Update the YUV shaders and the viewfinder_gl to correctly take the
Y'CbCr encoding and the quantization range into account when rendering
YUV formats to RGB. Support for the primaries and transfer function will
be added in a subsequent step.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Kunal Agarwal <kunalagarwal1072002@gmail.com>

3 files changed, 40 insertions, 33 deletions

diff --git a/src/qcam/assets/shader/YUV_2_planes.frag b/src/qcam/assets/shader/YUV_2_planes.frag
index 254463c0..da8dbcc5 100644
--- a/src/qcam/assets/shader/YUV_2_planes.frag
+++ b/src/qcam/assets/shader/YUV_2_planes.frag
@@ -13,27 +13,30 @@ varying vec2 textureOut;
 uniform sampler2D tex_y;
 uniform sampler2D tex_u;
 
+const mat3 yuv2rgb_matrix = mat3(
+	YUV2RGB_MATRIX
+);
+
+const vec3 yuv2rgb_offset = vec3(
+	YUV2RGB_Y_OFFSET / 255.0, 128.0 / 255.0, 128.0 / 255.0
+);
+
 void main(void)
 {
 	vec3 yuv;
-	vec3 rgb;
-	mat3 yuv2rgb_bt601_mat = mat3(
-		vec3(1.164,  1.164, 1.164),
-		vec3(0.000, -0.392, 2.017),
-		vec3(1.596, -0.813, 0.000)
-	);
-
-	yuv.x = texture2D(tex_y, textureOut).r - 0.063;
+
+	yuv.x = texture2D(tex_y, textureOut).r;
 #if defined(YUV_PATTERN_UV)
-	yuv.y = texture2D(tex_u, textureOut).r - 0.500;
-	yuv.z = texture2D(tex_u, textureOut).a - 0.500;
+	yuv.y = texture2D(tex_u, textureOut).r;
+	yuv.z = texture2D(tex_u, textureOut).a;
 #elif defined(YUV_PATTERN_VU)
-	yuv.y = texture2D(tex_u, textureOut).a - 0.500;
-	yuv.z = texture2D(tex_u, textureOut).r - 0.500;
+	yuv.y = texture2D(tex_u, textureOut).a;
+	yuv.z = texture2D(tex_u, textureOut).r;
 #else
 #error Invalid pattern
 #endif
 
-	rgb = yuv2rgb_bt601_mat * yuv;
+	vec3 rgb = yuv2rgb_matrix * (vec3(y, uv) - yuv2rgb_offset);
+
 	gl_FragColor = vec4(rgb, 1.0);
 }
diff --git a/src/qcam/assets/shader/YUV_3_planes.frag b/src/qcam/assets/shader/YUV_3_planes.frag
index 2be74b5d..e754129d 100644
--- a/src/qcam/assets/shader/YUV_3_planes.frag
+++ b/src/qcam/assets/shader/YUV_3_planes.frag
@@ -14,20 +14,23 @@ uniform sampler2D tex_y;
 uniform sampler2D tex_u;
 uniform sampler2D tex_v;
 
+const mat3 yuv2rgb_matrix = mat3(
+	YUV2RGB_MATRIX
+);
+
+const vec3 yuv2rgb_offset = vec3(
+	YUV2RGB_Y_OFFSET / 255.0, 128.0 / 255.0, 128.0 / 255.0
+);
+
 void main(void)
 {
 	vec3 yuv;
-	vec3 rgb;
-	mat3 yuv2rgb_bt601_mat = mat3(
-		vec3(1.164,  1.164, 1.164),
-		vec3(0.000, -0.392, 2.017),
-		vec3(1.596, -0.813, 0.000)
-	);
-
-	yuv.x = texture2D(tex_y, textureOut).r - 0.063;
-	yuv.y = texture2D(tex_u, textureOut).r - 0.500;
-	yuv.z = texture2D(tex_v, textureOut).r - 0.500;
-
-	rgb = yuv2rgb_bt601_mat * yuv;
+
+	yuv.x = texture2D(tex_y, textureOut).r;
+	yuv.y = texture2D(tex_u, textureOut).r;
+	yuv.z = texture2D(tex_v, textureOut).r;
+
+	vec3 rgb = yuv2rgb_matrix * (vec3(y, uv) - yuv2rgb_offset);
+
 	gl_FragColor = vec4(rgb, 1.0);
 }
diff --git a/src/qcam/assets/shader/YUV_packed.frag b/src/qcam/assets/shader/YUV_packed.frag
index d6efd4ce..b9ef9d41 100644
--- a/src/qcam/assets/shader/YUV_packed.frag
+++ b/src/qcam/assets/shader/YUV_packed.frag
@@ -14,15 +14,16 @@ varying vec2 textureOut;
 uniform sampler2D tex_y;
 uniform vec2 tex_step;
 
+const mat3 yuv2rgb_matrix = mat3(
+	YUV2RGB_MATRIX
+);
+
+const vec3 yuv2rgb_offset = vec3(
+	YUV2RGB_Y_OFFSET / 255.0, 128.0 / 255.0, 128.0 / 255.0
+);
+
 void main(void)
 {
-	mat3 yuv2rgb_bt601_mat = mat3(
-		vec3(1.164,  1.164, 1.164),
-		vec3(0.000, -0.392, 2.017),
-		vec3(1.596, -0.813, 0.000)
-	);
-	vec3 yuv2rgb_bt601_offset = vec3(0.063, 0.500, 0.500);
-
 	/*
 	 * The sampler won't interpolate the texture correctly along the X axis,
 	 * as each RGBA pixel effectively stores two pixels. We thus need to
@@ -76,7 +77,7 @@ void main(void)
 
 	float y = mix(y_left, y_right, step(0.5, f_x));
 
-	vec3 rgb = yuv2rgb_bt601_mat * (vec3(y, uv) - yuv2rgb_bt601_offset);
+	vec3 rgb = yuv2rgb_matrix * (vec3(y, uv) - yuv2rgb_offset);
 
 	gl_FragColor = vec4(rgb, 1.0);
 }