GLSL ray-sphere intersection

gistfile1.glsl

float raySphereIntersect(vec3 r0, vec3 rd, vec3 s0, float sr) {
    // - r0: ray origin
    // - rd: normalized ray direction
    // - s0: sphere center
    // - sr: sphere radius
    // - Returns distance from r0 to first intersecion with sphere,
    //   or -1.0 if no intersection.
    float a = dot(rd, rd);
    vec3 s0_r0 = r0 - s0;
    float b = 2.0 * dot(rd, s0_r0);
    float c = dot(s0_r0, s0_r0) - (sr * sr);
    if (b*b - 4.0*a*c < 0.0) {
        return -1.0;
    }
    return (-b - sqrt((b*b) - 4.0*a*c))/(2.0*a);
}

lol are we all using this for a shader in unity

Not me, I'm using it for Love2D.