// DISSOLVE — the plain crossfade as a TRANSITION DOC. Pattern taught: the
// two-deck `transition` engine. The host binds deck A/B into input 0/1 and
// sweeps p3 with the crossfader; the default `trans` hook of
// draw.DrawVjFxDuo IS a dissolve. The hook below reproduces it EXACTLY at
// the dial defaults and adds the mixer-desk levers: CURVE bends the fade
// law (fast-in vs fast-out), DIP ducks through black mid-fade, FLASH
// lifts to white mid-fade.
{
    name: "Crossfade"
    engine: "transition"
    p0: 0.5
    dials: [
        {name: "CURVE", bind: "p0", default: 0.5},
        {name: "DIP", bind: "p1", default: 0.0},
        {name: "FLASH", bind: "p2", default: 0.0}
    ]
    shader: draw.DrawVjFxDuo {
        trans: fn(uv: vec2, t: float) -> vec4 {
            // CURVE: exponent 0.25..4, exactly 1 (a plain mix) at 0.5.
            let tt = pow(clamp(t, 0.0, 1.0), pow(4.0, self.user.x * 2.0 - 1.0))
            let c = self.deck_a(uv).mix(self.deck_b(uv), tt)
            // Mid-fade envelope: 0 at the ends, 1 in the middle.
            let mid = 4.0 * tt * (1.0 - tt)
            let dim = 1.0 - mid * self.user.y * 0.9
            let flash = mid * self.user.z * 0.8
            return vec4(c.xyz * dim + vec3(1.0, 1.0, 1.0) * flash, 1.0)
        }
    }
}