// MULTIPLY — deck B darkens deck A wherever B itself is dark: the
// classic ink/paint combine, result = a*b (the inverse logic of the
// additive family at 109/112). GAIN pushes B's darkening hotter before
// the multiply, CURVE bends the fader response, KEY narrows the darken
// to B's own shadows only.
{
    name: "Multiply"
    engine: "transition"
    engage: "ramp"
    p1: 0.5
    dials: [
        {name: "GAIN", bind: "p0", default: 0.5},
        {name: "CURVE", bind: "p1", default: 0.5},
        {name: "KEY", bind: "p2", default: 0.0}
    ]
    shader: draw.DrawVjFxDuo {
        trans: fn(uv: vec2, t: float) -> vec4 {
            let a = self.deck_a(uv)
            let b = self.deck_b(uv)
            let gain = 0.5 + self.user.x * 1.5
            let tt = pow(clamp(t, 0.0, 1.0), pow(4.0, self.user.y * 2.0 - 1.0))
            let mult = a.xyz * clamp(b.xyz * gain, vec3(0.0, 0.0, 0.0), vec3(1.0, 1.0, 1.0))
            let luma = dot(b.xyz, vec3(0.2126, 0.7152, 0.0722))
            let gate = mix(1.0, 1.0 - smoothstep(0.25, 0.75, luma), self.user.z)
            let composite = a.xyz.mix(mult, tt * gate)
            return vec4(composite.x, composite.y, composite.z, 1.0)
        }
    }
}