It works!

data/blit.frag

@@ -0,0 +1,11 @@
+precision mediump float;
+
+uniform sampler2D texture;
+
+varying vec2 uv;
+
+#define fetch(p) texture2D(texture, p).r
+
+void main() {
+	gl_FragColor = texture2D(texture, uv);
+}

data/blit.vert

@@ -0,0 +1,12 @@
+precision mediump float;
+
+attribute vec2 vert;
+attribute vec2 tex_coord;
+
+varying vec2 uv;
+
+void main() {
+	uv = tex_coord;
+
+	gl_Position = vec4(vert, 0, 1);
+}

data/debayer.frag

@@ -1,36 +1,43 @@
-precision mediump float;
+precision highp float;
 
 uniform sampler2D texture;
-// uniform sampler2D srgb_map;
+uniform sampler2D pixel_layout;
 uniform mat3 color_matrix;
 
-varying vec2 uv1;
-varying vec2 uv2;
-varying vec2 pixel_coord;
+uniform vec2 pixel_size;
+
+// varying vec2 uv1;
+// varying vec2 uv2;
+varying vec2 top_left_uv;
+varying vec2 top_right_uv;
+varying vec2 bottom_left_uv;
+varying vec2 bottom_right_uv;
+varying vec2 half_pixel_coord;
 
 #define fetch(p) texture2D(texture, p).r
 
 void main() {
 	vec4 pixels = vec4(
-		fetch(uv1),
-		fetch(vec2(uv1.x, uv2.y)),
-		fetch(uv2),
-		fetch(vec2(uv2.x, uv1.y)));
+		fetch(top_left_uv),
+		fetch(top_right_uv),
+		fetch(bottom_right_uv),
+		fetch(bottom_left_uv));
 
-	vec2 arrangement = mod(pixel_coord, 2.0);
+	vec2 arrangement = floor(half_pixel_coord);
 
-	vec2 is_top_left = step(1.0, arrangement);
+	vec2 is_bottom_left = step(1.0, arrangement);
 
-	vec3 color = mix(
-		mix(pixels.zyx, pixels.wzy, is_top_left.y),
-		mix(pixels.yzw, pixels.xyz, is_top_left.y),
-		is_top_left.x);
+	// vec3 color = mix(
+	// 	mix(pixels.xyz, pixels.yzw, is_bottom_left.y),
+	// 	mix(pixels.wzy, pixels.zyx, is_bottom_left.y),
+	// 	is_bottom_left.x);
+	vec3 color = pixels.zyx;
 
-	vec3 srgb_color = pow(color, vec3(1.0 / 2.2));
-	// vec3 srgb_color = vec3(
-	// 	texture2D(srgb_map, vec2(color.r, 0)).r,
-	// 	texture2D(srgb_map, vec2(color.g, 0)).r,
-	// 	texture2D(srgb_map, vec2(color.b, 0)).r);
+	// Fast SRGB estimate. See https://mimosa-pudica.net/fast-gamma/
+	vec3 srgb_color = (vec3(1.138) * inversesqrt(color) - vec3(0.138)) * color;
 
-	gl_FragColor = vec4((color_matrix * srgb_color).bgr, 0);
+	// Slow SRGB estimate
+	// vec3 srgb_color = pow(color, vec3(1.0 / 2.2));
+
+	gl_FragColor = vec4(color_matrix * srgb_color, 0);
 }

data/debayer.vert

@@ -1,21 +1,32 @@
-precision mediump float;
+precision highp float;
 
 attribute vec2 vert;
 attribute vec2 tex_coord;
 
 uniform mat3 transform;
 uniform vec2 pixel_size;
+uniform vec2 half_image_size;
 
-varying vec2 uv1;
-varying vec2 uv2;
-varying vec2 pixel_coord;
+// varying vec2 uv1;
+// varying vec2 uv2;
+
+varying vec2 top_left_uv;
+varying vec2 top_right_uv;
+varying vec2 bottom_left_uv;
+varying vec2 bottom_right_uv;
+varying vec2 half_pixel_coord;
 
 void main() {
-	uv1 = tex_coord - pixel_size / 2.0;
-	uv2 = tex_coord + pixel_size / 2.0;
-	uv1 += pixel_size;
-	uv2 += pixel_size;
-	pixel_coord = uv1 / pixel_size;
+	top_left_uv = tex_coord - pixel_size / 2.0;
+	bottom_right_uv = tex_coord + pixel_size / 2.0;
+	top_right_uv = vec2(top_left_uv.x, bottom_right_uv.y);
+	bottom_left_uv = vec2(bottom_right_uv.x, top_left_uv.y);
+
+	// uv1 = tex_coord - pixel_size / 2.0;
+	// uv2 = tex_coord + pixel_size / 2.0;
+	// uv1 += pixel_size;
+	// uv2 += pixel_size;
+	half_pixel_coord = top_left_uv * half_image_size;
 
 	gl_Position = vec4(transform * vec3(vert, 1), 1);
 }