// NEGATIVE MIX — the MX50 party trick: deck B's brightness INVERTS deck A
// (solarize where B burns). At rest nothing; ride the fader into the burn.
{
    name: "Negative Mix"
    engine: "transition"
    // Overlay semantics: ridden to the fader's end the key STAYS fully
    // applied (the composite is the destination) — never a snap to
    // plain B. Zero only at the A end.
    engage: "ramp"
    p2: 0.5
    dials: [
        {name: "DRIVE", bind: "p0", default: 0.5},
        {name: "THRS", bind: "p1", default: 0.0},
        {name: "CURVE", bind: "p2", default: 0.5}
    ]
    shader: draw.DrawVjFxDuo {
        trans: fn(uv: vec2, t: float) -> vec4 {
            let a = self.deck_a(uv)
            let b = self.deck_b(uv)
            let luma = dot(b.xyz, vec3(0.2126, 0.7152, 0.0722))
            // THRS narrows the burn to B's highlights (0 = the stock
            // linear response).
            let l2 = mix(luma, smoothstep(0.3, 0.9, luma), self.user.y)
            // CURVE bends the fader response (1:1 at mid-knob).
            let tt = pow(clamp(t, 0.0, 1.0), pow(4.0, self.user.z * 2.0 - 1.0))
            let burn = clamp(l2 * (0.5 + self.user.x * 1.5) * tt, 0.0, 1.0)
            let neg = vec3(1.0, 1.0, 1.0) - a.xyz
            return vec4(a.xyz.mix(neg, burn), 1.0)
        }
    }
}