// TUMBLE AWAY — deck A is thrown: the card pitches and yaws at once while
// it falls back into the room, flashing its dimmed back face on every half
// turn, and deck B stands whole behind it the moment it clears.
//
// Pattern taught: the plane-in-3D helper (`plane_uv` below, the family's
// shared block — the reference copy lives in the Perspective doc). Camera
// at the origin looking down -z, one ray per fragment; the RAY and the EYE
// are pushed into the plane's own frame by the transposed rotation, where
// the plane is z = 0 and one divide gives the hit. Two axes turning at
// once is then just two more cosines — no matrices, no geometry.
//
// The back face is FREE: past edge-on the intersection reverses the axis
// it turned about, so the mirrored picture is already there. It is dimmed
// and drained of colour, which is what sells card stock rather than glass.
{
    name: "Tumble Away"
    engine: "transition"
    p0: 0.5
    dials: [
        {name: "TUMBLE", bind: "p0", default: 0.5},
        {name: "FLIP", bind: "p1", default: 0.0},
        {name: "DIP", bind: "p2", default: 0.0}
    ]
    shader: draw.DrawVjFxDuo {
        // ---- THE SHARED HELPER: one ray, one rotated video plane --------
        // The plane is the rectangle of half-extents (aspect, 1) * 0.5/f
        // whose HINGE sits at world (piv.x, piv.y, -d), spun about that
        // hinge by the Euler angles `ang` (Rz then Ry then Rx, radians).
        // Returns (plane u, plane v, on-quad 0/1, front-facing 0/1).
        plane_uv: fn(uv: vec2, ang: vec3, piv: vec2, d: float, f: float) -> vec4 {
            let a = self.aspect()
            let c0 = cos(ang.x)
            let s0 = sin(ang.x)
            let c1 = cos(ang.y)
            let s1 = sin(ang.y)
            let c2 = cos(ang.z)
            let s2 = sin(ang.z)
            // The ray through this fragment (y up) and the eye, both
            // measured from the hinge.
            let rd = vec3((uv.x - 0.5) * a, 0.5 - uv.y, 0.0 - f)
            let ro = vec3(0.0 - piv.x, 0.0 - piv.y, d)
            let r1 = vec3(rd.x * c2 + rd.y * s2, rd.y * c2 - rd.x * s2, rd.z)
            let o1 = vec3(ro.x * c2 + ro.y * s2, ro.y * c2 - ro.x * s2, ro.z)
            let r2 = vec3(r1.x * c1 - r1.z * s1, r1.y, r1.x * s1 + r1.z * c1)
            let o2 = vec3(o1.x * c1 - o1.z * s1, o1.y, o1.x * s1 + o1.z * c1)
            let r3 = vec3(r2.x, r2.y * c0 + r2.z * s0, r2.z * c0 - r2.y * s0)
            let o3 = vec3(o2.x, o2.y * c0 + o2.z * s0, o2.z * c0 - o2.y * s0)
            // Intersect z = 0. A ray running parallel to the plane is
            // NUDGED, never divided by zero — it lands far off the quad.
            let den = r3.z + (1.0 - step(0.0001, abs(r3.z))) * 0.001
            let k = 0.0 - o3.z / den
            let hx = o3.x + k * r3.x + piv.x
            let hy = o3.y + k * r3.y + piv.y
            let pu = hx * f / a + 0.5
            let pv = 0.5 - hy * f
            let onq = step(0.0, pu) * step(pu, 1.0) * step(0.0, pv) * step(pv, 1.0)
                * step(0.001, k)
            return vec4(pu, pv, onq, step(0.0, o3.z))
        }

        trans: fn(uv: vec2, t: float) -> vec4 {
            let tc = clamp(t, 0.0, 1.0)
            // The throw accelerates; the eased beat pulse gives it a shove
            // (pulse is 0..1, so the whole term stays bounded).
            let e = pow(tc, 1.35) * (1.0 + 0.14 * self.time_beat.w)
            let dir = mix(1.0, -1.0, step(0.5, self.user.y))
            let hard = clamp(self.user.x, 0.0, 1.0)
            // Two axes at once, deliberately detuned so the card never
            // repeats the same silhouette on the way out.
            let an = vec3(
                e * (1.0 + 2.4 * hard) * dir,
                e * (0.7 + 1.6 * hard),
                e * 0.55 * dir
            )
            let d = 1.0 + e * 1.9
            let p = self.plane_uv(uv, an, vec2(0.0, 0.0), d, 1.12)
            // Guarantee the far end: the last of the card is gone by t = 1.
            let vis = p.z * (1.0 - smoothstep(0.84, 1.0, tc))
            let ca = self.deck_a(vec2(p.x, p.y))
            // Back face: mirrored for free, dimmed and drained.
            let lum = dot(ca.xyz, vec3(0.299, 0.587, 0.114))
            let back = mix(ca.xyz, vec3(lum, lum, lum), 0.5) * 0.30
            let card = mix(back, ca.xyz, p.w)
            let ed = min(min(p.x, 1.0 - p.x), min(p.y, 1.0 - p.y))
            let rim = (1.0 - smoothstep(0.0, 0.006, ed)) * vis
            let mut c = mix(self.deck_b(uv).xyz, card, vis)
            c = c + vec3(1.0, 1.0, 1.0) * (rim * 0.35)
            // DIP: duck through black mid-tumble (0 = off, the stock look).
            let dim = 1.0 - 4.0 * tc * (1.0 - tc) * self.user.z * 0.9
            return vec4(c * dim, 1.0)
        }
    }
}