sphere.glsl

struct Ray {
    vec3 origin;
    vec3 direction;
};

    
bool intersectRaySphere(out vec3 intersection, in Ray ray, in vec3 center, in float radius) {
    vec3 o = center - ray.origin;
    float d2 = dot(ray.direction, ray.direction);
    float r2 = radius * radius;
    float l2 = dot(o, o);
    float dp = dot(ray.direction, o);
    float delta = dp * dp / d2 - l2 + r2;

    if (delta < 0.0) {
        return false;
    }

    float lambda = dp / d2 - sqrt(delta / d2);
    intersection = ray.origin + lambda * ray.direction;
    return true;
}


void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
	vec2 uv = fragCoord.xy / iResolution.xy;
	fragColor = vec4(uv,0.5+0.5*sin(iTime),1.0);
    
    vec2 f = 0.1 * iResolution.xx/iResolution.xy;
    mat3 m = mat3(
        1.0, 0.0, 0.0,
        0.0, 0.0, 1.0,
        0.0, 1.0, 0.0
    );
    Ray ray = Ray(
        vec3(0.0, -0.6, 0.0),
        m * vec3((uv*2.0-1.0) / f, -1.0)
    );
    
    vec3 intersection;
    if (intersectRaySphere(intersection, ray, vec3(0.0), 0.5)) {
        fragColor = vec4(0.0);
    }
}