// BOX IRIS — the square sibling of the circular iris: a Chebyshev
// (square) distance field instead of a radial one, so the aperture
// opens as a square rather than a circle. FLIP closes deck A instead.
{
    name: "Box Iris"
    engine: "transition"
    dials: [
        {name: "SOFT", bind: "p0", default: 0.15},
        {name: "FLIP", bind: "p1", default: 0.0},
        {name: "DIP", bind: "p2", default: 0.0}
    ]
    shader: draw.DrawVjFxDuo {
        trans: fn(uv: vec2, t: float) -> vec4 {
            let c2 = vec2((uv.x - 0.5) * self.aspect(), uv.y - 0.5)
            let field = max(abs(c2.x), abs(c2.y))
            let rmax = 0.5 * max(self.aspect(), 1.0)
            let soft = 0.005 + self.user.x * 0.2
            let flip = step(0.5, self.user.y)
            let tt = mix(t, 1.0 - t, flip)
            let edge = tt * (rmax + 2.0 * soft) - soft
            let inside = smoothstep(edge + soft, edge - soft, field)
            let cin = self.deck_b(uv).mix(self.deck_a(uv), flip)
            let cout = self.deck_a(uv).mix(self.deck_b(uv), flip)
            let c = cout.mix(cin, inside)
            let dim = 1.0 - 4.0 * clamp(t, 0.0, 1.0) * (1.0 - clamp(t, 0.0, 1.0)) * self.user.z * 0.9
            return vec4(c.xyz * dim, 1.0)
        }
    }
}