Make it twist

Twist amount:

The twist effect looks visually complicated, but it only requires a few lines of code. Here's the new map function that produces the twist effect in the example above:

vec2 map (vec3 p, float time) 
{ 
    vec2 res = vec2(1e10, 0.0);

    p = p + vec3(0.0, 0.0, 15.0);

    // twist
    float k = uSlider / 40.0; 
    float c = cos(k*p.y);
    float s = sin(k*p.y);
    mat2  m = mat2(c,-s,s,c);
    vec3 twisted = vec3(m*p.xz,p.y);

    res = vec2(sdRoundBox(twisted, vec3(0.5), 0.0), 15.0);

    return res;
}

k corresponds to the amount of the twist you want to add. In this example, the input slider value determines k.

tip

Try varying k over time! For example, set k = sin(time).

Here's the key intuition: you don't need to derive a new distance function for the twisted shape. Instead, modify space by rotating the position vector, p, around the y axis, varying the degree of rotation by the magnitude of y. Then pass the rotated vector into the distance function for the "un-twisted" shape, which in this case is the box from the starter example.

tip

In the map function, we build a rotation matrix and use it to rotate p around the y axis. Try modifying the code to rotate around the x axis instead!