// FRESNEL — the frame reads through concentric fresnel-lens steps: radius
// is quantised into rings, each ring bends its sample and carries a seam.
{
    name: "Fresnel"
    engine: "screen"
    input0: "test"

    p0: 0.5  p1: 0.5  p2: 0.5
    dials: [
        {name: "RINGS", bind: "p0", default: 0.5},
        {name: "DEPTH", bind: "p1", default: 0.5},
        {name: "SPIN", 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 center = vec2(0.5, 0.5)
            let d = uv - center
            let r = length(d)
            let ang = atan2(d.y, d.x)
            let rings = 6.0 + 28.0 * self.user.x
            let stepr = floor(r * rings) / rings
            let fracr = fract(r * rings)
            let depth = 0.01 + 0.05 * self.user.y
            let bend = (fracr - 0.5) * depth * (0.7 + 0.3 * self.time_beat.w)
            let newr = clamp(stepr + bend, 0.0, 0.75)
            let swirl = (1.0 - stepr) * self.user.z * 1.2 * (0.5 + 0.5 * self.time_beat.w)
            let newang = ang + swirl
            let w = center + vec2(cos(newang), sin(newang)) * newr
            let tex = self.tex0.sample_as_bgra(clamp(w, vec2(0.0, 0.0), vec2(1.0, 1.0)))
            let seam = 1.0 - smoothstep(0.0, 0.05, min(fracr, 1.0 - fracr))
            let out = tex.xyz + vec3(1.0, 1.0, 1.0) * seam * 0.14
            return vec4(out, 1.0)
        }
    }
}