// WIPE — the classic left-to-right edge. Pattern taught: subclassing the
// duo compositor's `trans` hook. `t` is the crossfader 0→1; return deck A
// at 0 and deck B at 1. SOFT feathers the edge, FLIP reverses direction.
{
    name: "Wipe"
    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 x = mix(uv.x, 1.0 - uv.x, step(0.5, self.user.y))
            let soft = 0.004 + self.user.x * 0.25
            // Widen the sweep so the edge fully clears both ends even
            // with a fat feather.
            let tt = t * (1.0 + 2.0 * soft) - soft
            let m = smoothstep(tt - soft, tt + soft, x)
            let c = self.deck_b(uv).mix(self.deck_a(uv), m)
            // DIP: duck through black mid-fade (0 = off, the stock wipe).
            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)
        }
    }
}