// KEYED TRAILS — only the bright part of the picture leaves a trail: a
// luma key isolates the subject before the feedback stage sees the
// frame, so dim background never smears while a hot subject glows on
// after it moves.
{
    name: "Keyed Trails"
    engine: "screen"
    seed: 207
    input0: "test"

    speed: 1.0
    beat_pulse: 0.4
    beat_rate: 1.0
    bar_beats: 4
    glow: 1.0
    // PERFORMANCE DIALS — mid-knob = the stock look, exact.
    p0: 0.5  p1: 0.5  p2: 0.5
    dials: [
        {name: "KEY", bind: "p0", default: 0.5},
        {name: "SOFT", bind: "p1", default: 0.5},
        {name: "GLOW", bind: "p2", default: 0.5}
    ]

    color_bg: #x03040a
    color_a: #x30ffd0
    color_b: #xff3a86
    color_c: #xfff0d0

    stages: [
        {kind: "feedback", amount: "min((0.55 + pulse * 0.2) * (0.25 + 1.5*p2), 0.95)", zoom: 1.012,
         rotate: "sin(bar * tau) * 0.008", dim: 0.95}
    ]

    // THE LOOK LIVES HERE: fx_color decides what the feedback stage
    // actually sees. Pixels above the KEY threshold burn hot into the
    // scene (and so into next frame's trail); pixels below it are
    // dimmed so they contribute almost nothing to the trail buildup.
    // Inputs: uv, content = input0 at uv, cmix = pre-gated content
    // strength. Signals: self.time_beat (time, beat, phase, pulse),
    // self.sig (bar, bpm, energy, dt), self.user (p0..p3),
    // self.col_a/b/c/bg, self.fog (density, glow, content, -).
    shader: draw.DrawVjFxScreen {
        fx_color: fn(uv: vec2, content: vec4, cmix: float) -> vec4 {
            let luma = dot(content.xyz, vec3(0.299, 0.587, 0.114))
            let thresh = 0.15 + 0.6 * clamp(self.user.x, 0.0, 1.0)
            let soft = 0.02 + 0.25 * clamp(self.user.y, 0.0, 1.0)
            let key = smoothstep(thresh - soft, thresh + soft, luma)
            let boost = 1.0 + 2.0 * clamp(self.user.z, 0.0, 1.0)
            let base = content.xyz * (0.3 + 0.55 * (1.0 - key))
            let hot = content.xyz * boost * key
            return vec4(clamp(base + hot, vec3(0.0, 0.0, 0.0), vec3(1.0, 1.0, 1.0)), 1.0)
        }
    }
}