fisheye.cikernel

kernel vec4 fisheye(sampler img, float signcurvature, float lensradius)
{
    // no constants/defines?
    float EPSILON = 0.000011;
    float otherConst = 1.4427;


    float curvature = abs(signcurvature);
    float extent = lensradius;
    float optics = extent / log2(curvature * extent + 1.0) / otherConst;
    
    vec2 normalizeTD = samplerCoord( img ) / samplerSize( img );

    vec2 PP = normalizeTD - vec2(0.5,0.5);
    float P0 = PP[0];
    float P1 = PP[1];
    float radius = sqrt(P0 * P0 + P1 * P1);

    float cosangle = P0 / radius;
    float sinangle = P1 / radius;

    float rad1, rad2, newradius;
    rad1 = (exp2((radius / optics) * otherConst) - 1.0) / curvature;
    rad2 = optics * log2(1.0 + curvature * radius) / otherConst;
    newradius = signcurvature > 0.0 ? rad1 : rad2;

    vec2 FE = vec2(newradius * cosangle + 0.5,newradius * sinangle + 0.5);
    FE = radius <= extent ? FE : normalizeTD;
    FE = curvature < EPSILON ? normalizeTD : FE;

    vec2 xformedCoord = FE * samplerSize( img );
    return sample(img, xformedCoord);
}