const ivec2 half_size = imageSize(output_images[idx]) / 2;
    const float z = dot(half_size, half_size);
    float p = ((open ? (1.0 - progress) : progress) - 0.5) * 3.0;
    ivec2 dsize = pos - half_size;
    float sm = dot(dsize, dsize) / z + p;
    vec4 a = texture(a_images[idx], pos);
    vec4 b = texture(b_images[idx], pos);
    imageStore(output_images[idx], pos, mix(open ? b : a, open ? a : b, smoothstep(0.f, 1.f, sm)));
}
void transition(int idx, ivec2 pos, float progress)
{
    circle(idx, pos, progress, false);
}