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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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