// VORTEX — the frame sucks around a pivot that sits off-centre and drifts
// slowly on an ellipse; rotation is strongest near the pivot and fades out.
{
    name: "Vortex"
    engine: "screen"
    input0: "test"

    p0: 0.5  p1: 0.5  p2: 0.5
    dials: [
        {name: "STRENGTH", bind: "p0", default: 0.5},
        {name: "REACH", bind: "p1", default: 0.5},
        {name: "DRIFT", bind: "p2", default: 0.5}
    ]

    stages: [
        {kind: "bloom", threshold: 0.6, strength: 1.05, levels: 2}
    ]

    shader: draw.DrawVjFxScreen {
        fx_color: fn(uv: vec2, content: vec4, cmix: float) -> vec4 {
            let speed = 0.06 + 0.3 * self.user.z
            let pang = self.time_beat.x * speed
            let pivot = vec2(0.5, 0.5) + vec2(cos(pang), sin(pang) * 0.8) * 0.16
            let d = uv - pivot
            let r = length(d)
            let reach = 0.22 + 0.4 * self.user.y
            let falloff = clamp(1.0 - r / reach, 0.0, 1.0)
            let spin = falloff * falloff * (3.0 + 7.0 * self.user.x) * (0.5 + 0.5 * self.time_beat.w)
            let cs = cos(spin)
            let sn = sin(spin)
            let rd = vec2(d.x * cs - d.y * sn, d.x * sn + d.y * cs)
            let w = pivot + rd
            let tex = self.tex0.sample_as_bgra(clamp(w, vec2(0.0, 0.0), vec2(1.0, 1.0)))
            return vec4(tex.xyz, 1.0)
        }
    }
}