// Folds the picture into mirrored wedges around the centre.
// order 90
// slider segments 2.0 16.0 6.0
// slider spin -2.0 2.0 0.2
float4 effect(float2 uv, Inputs in) {
    float2 shape = float2(in.resolution.x / in.resolution.y, 1.0);
    float2 c = (uv - 0.5) * shape;
    float wedge = 6.2832 / floor(in.p.segments);
    float a = atan2(c.y, c.x) + in.time * in.p.spin;
    a = abs(a - wedge * floor(a / wedge) - wedge * 0.5) - 1.5708;  // fold into one mirrored wedge, pointing up
    float2 from = float2(cos(a), sin(a)) * length(c) / shape + 0.5;
    return float4(in.image.sample(in.smp, from).rgb, 1.0);
}