// SHIFT WIPE — a diagonal gradient sheared by SHEAR: at 0 it's a plain
// horizontal wipe, dialled up it leans the seam into a steep diagonal.
// FLIP reverses the sweep direction.
{
    name: "Shift Wipe"
    engine: "transition"
    dials: [
        {name: "SOFT", bind: "p0", default: 0.12},
        {name: "SHEAR", bind: "p1", default: 0.4},
        {name: "FLIP", bind: "p2", default: 0.0}
    ]
    shader: draw.DrawVjFxDuo {
        trans: fn(uv: vec2, t: float) -> vec4 {
            let shear = (self.user.y - 0.5) * 2.0
            let raw = uv.x + shear * uv.y
            let lo = min(0.0, shear)
            let hi = 1.0 + max(0.0, shear)
            let mut field = clamp((raw - lo) / max(hi - lo, 0.001), 0.0, 1.0)
            field = mix(field, 1.0 - field, step(0.5, self.user.z))
            let soft = 0.01 + self.user.x * 0.3
            let tt = t * (1.0 + 2.0 * soft) - soft
            let m = smoothstep(tt - soft, tt + soft, field)
            return self.deck_b(uv).mix(self.deck_a(uv), m)
        }
    }
}