Fisheye to spherical conversion shader

fisheye2spherical.frag

// Fisheye to spherical conversion
// Assumes the fisheye image is square, centered, and the circle fills the image.
// Output (spherical) image should have 2:1 aspect.
// Strange (but helpful) that atan() == atan2(), normally they are different.
//Refer http://blog.yeezia.com/?post=91
kernel vec4 fish2sphere(sampler src)
{
 vec2 pfish;
 float theta,phi,r;
 vec3 psph;
 float FOV = 3.141592654; // FOV of the fisheye, eg: 180 degrees
 float width = samplerSize(src).x;
 float height = samplerSize(src).y;
 // Polar angles
 theta = 2.0 * 3.14159265 * (destCoord().x / width - 0.5); // -pi to pi
 phi = 3.14159265 * (destCoord().y / height - 0.5); // -pi/2 to pi/2
 // Vector in 3D space
 psph.x = cos(phi) * sin(theta);
 psph.y = cos(phi) * cos(theta);
 psph.z = sin(phi);
 // Calculate fisheye angle and radius
 theta = atan(psph.z,psph.x);
 phi = atan(sqrt(psph.x*psph.x+psph.z*psph.z),psph.y);
 r = width * phi / FOV; 
 // Pixel in fisheye space
 pfish.x = 0.5 * width + r * cos(theta);
 pfish.y = 0.5 * width + r * sin(theta);
 return sample(src, pfish);
}