gistfile1.txt

varying highp vec2 textureCoordinate;

uniform sampler2D inputImageTexture;

#define M_PI 3.1415926535897932384626433832795

void main()
{
    highp vec2 centered = textureCoordinate - vec2(0.5, 0.5);
    
    highp float angle = atan(centered.y, centered.x) / (M_PI * 2.0) + 0.5;
    highp float mag   = length(centered) * 2.0;
    
    gl_FragColor = texture2D(inputImageTexture, vec2(angle, mag));
}