// ZOOM IN — deck B is a card far back in the room that RUSHES the camera
// and lands flush on the frame. It is not a scale: the card is at a real
// distance and its size is the perspective divide, so it grows the way
// something coming at you grows — slow while it is far, then all at once.
//
// 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; 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. Distance enters as `d` alone, and d = 1
// with no rotation returns `uv` EXACTLY — which is why the landing is deck
// B to the pixel. The approach is geometric (d = depth^(1-t)) because a
// linear one crawls in and then slams.
{
    name: "Zoom In"
    engine: "transition"
    p0: 0.5  p1: 0.5
    dials: [
        {name: "DEPTH", bind: "p0", default: 0.5},
        {name: "SPIN", bind: "p1", default: 0.5},
        {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)
            // DEPTH: 4..18 units back. Geometric approach — equal ratios
            // per unit of fader, which is what reads as constant speed.
            let far = 4.0 + 14.0 * clamp(self.user.x, 0.0, 1.0)
            let d = pow(far, 1.0 - tc)
            // SPIN is bipolar: mid-knob = no roll, either side rolls the
            // card in. Whatever it is, it unwinds to zero on landing.
            let sp = (self.user.y - 0.5) * 2.6
            // A vanishing lean, so the card is visibly a PLANE in a room
            // on the way in and dead flush when it arrives.
            let lean = (1.0 - tc) * 0.14
            let an = vec3(lean, lean * 0.7, (1.0 - tc) * sp)
            let p = self.plane_uv(uv, an, vec2(0.0, 0.0), d, 1.12)
            // Guarantee the near end: nothing of B at t = 0.
            let vis = p.z * smoothstep(0.0, 0.03, tc)
            let cb = self.deck_b(vec2(p.x, p.y))
            // The back face (only ever seen at extreme SPIN) is mirrored
            // for free by the intersection; it is just dimmed.
            let card = cb.xyz * mix(0.34, 1.0, p.w)
            // A hairline rim so the card has an edge against deck A.
            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 * (1.0 - tc)
            let mut c = mix(self.deck_a(uv).xyz, card, vis)
            c = c + vec3(1.0, 1.0, 1.0) * (rim * 0.4)
            // DIP: duck through black mid-rush (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)
        }
    }
}