From 1a9569912879f52c69a6f301719e5b543fe86cc6 Mon Sep 17 00:00:00 2001
From: datenwolf <@datenwolf.net>
Date: Thu, 3 Jul 2025 00:19:42 +0200
Subject: base commit, SDL2, EGL and OpenGL-ES 2 setup, texture upload and
 basic de-Bayer

---
 debayer.fs.glsl | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 debayer.fs.glsl

(limited to 'debayer.fs.glsl')

diff --git a/debayer.fs.glsl b/debayer.fs.glsl
new file mode 100644
index 0000000..e6eace4
--- /dev/null
+++ b/debayer.fs.glsl
@@ -0,0 +1,41 @@
+uniform sampler2D u_sampler;
+uniform highp mat4 u_coef_r;
+uniform highp mat4 u_coef_g;
+uniform highp mat4 u_coef_b;
+varying highp vec2 v_position;
+
+/* Evaluate power serial polynomial of degree 16, with 0-th order term 0 */
+highp float polyeval(highp mat4 c, highp float x){
+	highp float y = c[3][3];
+	for(int i=4, j=3; 0<i; --i, j=4){ for(; 0<j; --j){
+		y = y*x + c[i-1][j-1];
+	}}
+	return y*x;
+}
+
+void main(){
+	/* Even and odd rows each contain alternating primitives of the
+	 * Bayer pattern;
+	 * RGRGRGRGRG
+	 * GBGBGBGBGB
+	 * RGRGRGRGRG
+	 * GBGBGBGBGB
+	 * ...
+	 *
+	 * The pixel data was uploaded to the texture in
+	 * a way, that the even rows are in 0<x<0.5 and the odd rows
+	 * in 0.5<x<1, i.e. we end up with
+	 * RGRGRGRGRG GBGBGBGBGB
+	 * RGRGRGRGRG GBGBGBGBGB
+	 * ...
+	 *
+	 * Also OpenGL assumes texture origin lower left, so flip y here */
+	lowp vec2 v_pos_even = vec2(0.5*(   v_position.x), 1.-v_position.y);
+	lowp vec2 v_pos_odd  = vec2(0.5*(1.+v_position.x), 1.-v_position.y);
+	highp vec4 rggb = vec4(texture2D(u_sampler, v_pos_even).wx, texture2D(u_sampler, v_pos_odd ).wx);
+	highp vec3 rgb  = vec3(
+	       polyeval(u_coef_r, rggb[0]),
+	       mix(polyeval(u_coef_g, rggb[1]), polyeval(u_coef_g, rggb[2]), 0.5),
+	       polyeval(u_coef_b, rggb[3]) );
+	gl_FragColor = vec4(rgb, 1.);
+}
-- 
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