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);
}

In your comment it says rd: normalized ray direction, but then you compute dot(rd, rd) which is always one. So either rd should not be normalized or your code is doing unnecessary operations.

lol are we all using this for a shader in unity

lol are we all using this for a shader in unity

Not me, I'm using it for Love2D.