improve chromatic abberation shader

shaders/postfx_chromaticaberration.frag

@@ -3,19 +3,55 @@ in vec2 f_coords;
 layout(location = 0) out vec4 out_color;
 
 #texture (color_tex, 0, RGB)
+
 uniform sampler2D iChannel0;
 
+vec2 barrelDistortion(vec2 f_coords, float amt) {
+	vec2 cc = f_coords - 0.5;
+	float dist = dot(cc, cc);
+	return f_coords + cc * dist * amt;
+}
+
+float sat( float t )
+{
+	return clamp( t, 0.0, 1.0 );
+}
+
+float linterp( float t ) {
+	return sat( 1.0 - abs( 1.0*t - 1.0 ) );
+}
+
+float remap( float t, float a, float b ) {
+	return sat( (t - a) / (b - a) );
+}
+
+vec4 spectrum_offset( float t ) {
+	vec4 ret;
+	float lo = step(t,0.5);
+	float hi = 1.0-lo;
+	float w = linterp( remap( t, 1.0/6.0, 5.0/6.0 ) );
+	ret = vec4(lo,1.0,hi, 1.) * vec4(1.0-w, w, 1.0-w, 1.);
+
+	return pow( ret, vec4(1.0/2.2) );
+}
+
+const float max_distort = 0.05;
+const int num_iter = 10;
+const float reci_num_iter_f = 1.0 / float(num_iter);
+
 void main()
 {	
-	float amount = 0.001;
+	vec2 uv=f_coords.xy;
 
-	vec2 uv = f_coords;
-	vec3 col;
-	col.r = texture( iChannel0, vec2(uv.x+amount,uv.y) ).r;
-	col.g = texture( iChannel0, uv ).g;
-	col.b = texture( iChannel0, vec2(uv.x-amount,uv.y) ).b;
-
-	col *= (1.0 - amount * 0.5);
-	
-	out_color = vec4(col,1.0);
+	vec4 sumcol = vec4(0.0);
+	vec4 sumw = vec4(0.0);	
+	for ( int i=0; i<num_iter;++i )
+	{
+		float t = float(i) * reci_num_iter_f;
+		vec4 w = spectrum_offset( t );
+		sumw += w;
+		sumcol += w * texture( iChannel0, barrelDistortion(uv, .6 * max_distort*t ) );
+	}
+		
+	out_color = sumcol / sumw;
 }