qcam: viewfinder_gl: Add shader to render packed YUV formats

The shader supports all 4 packed 8-bit YUV variants.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

2 files changed, 83 insertions, 0 deletions

diff --git a/src/qcam/assets/shader/YUV_packed.frag b/src/qcam/assets/shader/YUV_packed.frag
new file mode 100644
index 00000000..224dfafe
--- /dev/null
+++ b/src/qcam/assets/shader/YUV_packed.frag
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Laurent Pinchart <laurent.pinchart@ideasonboard.com>
+ *
+ * YUV_packed.frag - Fragment shader code for YUYV packed formats
+ */
+
+#ifdef GL_ES
+precision mediump float;
+#endif
+
+varying vec2 textureOut;
+
+uniform sampler2D tex_y;
+uniform float tex_stepx;
+
+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
+	 * interpolate manually.
+	 *
+	 * In integer texture coordinates, the Y values are layed out in the
+	 * texture memory as follows:
+	 *
+	 * ...| Y  U  Y  V | Y  U  Y  V | Y  U  Y  V |...
+	 * ...| R  G  B  A | R  G  B  A | R  G  B  A |...
+	 *      ^     ^      ^     ^      ^     ^
+	 *      |     |      |     |      |     |
+	 *     n-1  n-0.5    n   n+0.5   n+1  n+1.5
+	 *
+	 * For a texture location x in the interval [n, n+1[, sample the left
+	 * and right pixels at n and n+1, and interpolate them with
+	 *
+	 * left.r * (1 - a) + left.b * a	if fract(x) < 0.5
+	 * left.b * (1 - a) + right.r * a	if fract(x) >= 0.5
+	 *
+	 * with a = fract(x * 2) which can also be written
+	 *
+	 * a = fract(x) * 2			if fract(x) < 0.5
+	 * a = fract(x) * 2 - 1			if fract(x) >= 0.5
+	 */
+	vec2 pos = textureOut;
+	float f_x = fract(pos.x / tex_stepx);
+
+	vec4 left = texture2D(tex_y, vec2(pos.x - f_x * tex_stepx, pos.y));
+	vec4 right = texture2D(tex_y, vec2(pos.x + (1.0 - f_x) * tex_stepx , pos.y));
+
+#if defined(YUV_PATTERN_UYVY)
+	float y_left = mix(left.g, left.a, f_x * 2.0);
+	float y_right = mix(left.a, right.g, f_x * 2.0 - 1.0);
+	vec2 uv = mix(left.rb, right.rb, f_x);
+#elif defined(YUV_PATTERN_VYUY)
+	float y_left = mix(left.g, left.a, f_x * 2.0);
+	float y_right = mix(left.a, right.g, f_x * 2.0 - 1.0);
+	vec2 uv = mix(left.br, right.br, f_x);
+#elif defined(YUV_PATTERN_YUYV)
+	float y_left = mix(left.r, left.b, f_x * 2.0);
+	float y_right = mix(left.b, right.r, f_x * 2.0 - 1.0);
+	vec2 uv = mix(left.ga, right.ga, f_x);
+#elif defined(YUV_PATTERN_YVYU)
+	float y_left = mix(left.r, left.b, f_x * 2.0);
+	float y_right = mix(left.b, right.r, f_x * 2.0 - 1.0);
+	vec2 uv = mix(left.ag, right.ag, f_x);
+#else
+#error Invalid pattern
+#endif
+
+	float y = mix(y_left, y_right, step(0.5, f_x));
+
+	vec3 rgb = yuv2rgb_bt601_mat * (vec3(y, uv) - yuv2rgb_bt601_offset);
+
+	gl_FragColor = vec4(rgb, 1.0);
+}
diff --git a/src/qcam/assets/shader/shaders.qrc b/src/qcam/assets/shader/shaders.qrc
index 7010d843..857ed9fd 100644
--- a/src/qcam/assets/shader/shaders.qrc
+++ b/src/qcam/assets/shader/shaders.qrc
@@ -4,5 +4,6 @@
 	<file>YUV.vert</file>
 	<file>YUV_2_planes.frag</file>
 	<file>YUV_3_planes.frag</file>
+	<file>YUV_packed.frag</file>
 </qresource>
 </RCC>