raymarch_test.glsl

float udBox( vec3 p, vec3 b ) {
  return length(max(abs(p)-b,0.0));
}

float sdTorus( vec3 p, vec2 t )
{
  vec2 q = vec2(length(p.xz)-t.x,p.y);
  return length(q)-t.y;
}

vec3 rot(vec3 s, float th)
{
	return mat3(1, 0, 0,
                0, cos(th), -sin(th),
                0, sin(th), cos(th)
                ) * s;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    float t = -iTime;
    vec3 eye = vec3(3. * cos(t), 0, 3. * sin(t));
    vec3 up = vec3(0, 1, 0);
    vec3 right = vec3(-sin(t), 0, cos(t));
    
    float u = fragCoord.x * 2.0 / iResolution.x - 1.0;
    float v = fragCoord.y * 2.0 / iResolution.x - 0.5;
    vec3 forward = eye - right * u + up * v;
    float f = length(forward);
    vec3 ro = eye + forward * f;
    vec3 rd = normalize(cross(right, up));

    vec4 color = vec4(0.0); // Sky color

    float ct = 0.0;
    const int maxSteps = 32;
    for(int i = 0; i < maxSteps; ++i)
    {
        vec3 p = ro + rd * ct;
        float ds = length(p - 1.0 /*+ 0.5 * sin(iTime)*/) - 0.5;
        p = rot(p, 0.5);
        float dt = sdTorus(p, vec2(0.5));
        float d = min(ds, dt);
        if(d < 1e-5)
        {
            color = vec4(1.0 - float(i) / float(maxSteps));
            break;
        }

        ct += d;
    }

    fragColor = color;
}