The ground gets cast: per-pixel floor and ceiling, both paintable

True floor-casting replaces the gradients and the projected seam lines:
every screen row lies at one depth, walked with a constant world-space
step and sampled from floor.png underfoot and ceiling.png overhead —
each maze cell wearing exactly one tile, so the artist's border IS the
cell seam. Distance shade and fog fold into the same per-pixel pass,
pixel buffers cache per texture (re-read when a painted file lands),
and the whole frame still clears 60fps with room to spare. Flagstones
and dark slabs ship as the starter files beside the other masonry.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/web/src/TokenGallery.svelte

@@ -94,7 +94,7 @@
     wherever a file is missing.
   </p>
   <div class="grid">
-    {#each ["wall", "rim", "stone", "door", "firewall", "warp"] as name (name)}
+    {#each ["wall", "rim", "stone", "door", "firewall", "warp", "floor", "ceiling"] as name (name)}
       <figure>
         <img class="masonry" src={`/textures/${name}.png`} alt={`${name} texture`} />
         <figcaption>{name}</figcaption>

packages/web/src/fpv/FirstPerson.svelte

@@ -58,57 +58,83 @@
   // so a missing or still-loading file never leaves a wall naked.
   const textures = materialTextures();
 
+  // Floor-casting samples per PIXEL, so the two ground-plane textures are
+  // cached as raw pixel buffers — re-extracted whenever a painted file
+  // finishes loading and swaps the entry.
+  const pixelCache = new WeakMap<object, ImageData>();
+  function pixelsOf(src: CanvasImageSource & { width: number; height: number }): ImageData {
+    let px = pixelCache.get(src);
+    if (!px) {
+      const t = document.createElement("canvas");
+      t.width = src.width;
+      t.height = src.height;
+      const c = t.getContext("2d")!;
+      c.drawImage(src, 0, 0);
+      px = c.getImageData(0, 0, t.width, t.height);
+      pixelCache.set(src, px);
+    }
+    return px;
+  }
+  let frame: ImageData | null = null;
+
   function draw(time: number) {
     const ctx = canvas?.getContext("2d");
     if (!ctx) return;
     ctx.imageSmoothingEnabled = false; // crisp texels, as the old masters drew
     const W = width, H = height, half = H / 2;
 
-    // Sky and floor: torchlight fading to the dark of the maze.
-    const sky = ctx.createLinearGradient(0, 0, 0, half);
-    sky.addColorStop(0, "#0d0c12");
-    sky.addColorStop(1, "#2a2620");
-    ctx.fillStyle = sky;
-    ctx.fillRect(0, 0, W, half);
-    const floor = ctx.createLinearGradient(0, half, 0, H);
-    floor.addColorStop(0, "#2b251c");
-    floor.addColorStop(1, "#463c2c");
-    ctx.fillStyle = floor;
-    ctx.fillRect(0, half, W, H - half);
-
-    // The floor's tile seams: grid lines projected onto the ground plane,
-    // drawn before the walls so the walls occlude what stands behind them.
+    // The ground and the vault overhead, cast per pixel: each screen row
+    // below (or above) the horizon lies at one fixed depth, so the row is
+    // walked with a constant world-space step and sampled from the floor
+    // or ceiling texture — every maze cell wearing one full tile of it.
     const fx = (W / 2) / Math.tan(FOV / 2);
     const cosF = Math.cos(facing), sinF = Math.sin(facing);
-    const toCam = (wx: number, wy: number) => {
-      const rx = wx - x, ry = wy - y;
-      return { fwd: rx * cosF + ry * sinF, side: -rx * sinF + ry * cosF };
-    };
-    ctx.lineWidth = 1;
-    const seg = (ax: number, ay: number, bx: number, by: number) => {
-      let a = toCam(ax, ay), b = toCam(bx, by);
-      const NEAR = 0.12;
-      if (a.fwd < NEAR && b.fwd < NEAR) return;
-      if (a.fwd < NEAR || b.fwd < NEAR) {
-        const t = (NEAR - a.fwd) / (b.fwd - a.fwd);
-        const cut = { fwd: NEAR, side: a.side + (b.side - a.side) * t };
-        if (a.fwd < NEAR) a = cut; else b = cut;
+    if (!frame || frame.width !== W || frame.height !== H) frame = ctx.createImageData(W, H);
+    const buf = frame.data;
+    const fl = pixelsOf(textures.floor!);
+    const ce = pixelsOf(textures.ceiling!);
+    const FOG = 13;
+    for (let row = 0; row < H; row++) {
+      const below = row > half;
+      const dz = below ? row - half : half - row;
+      if (dz < 1) {
+        // The horizon sliver: fog it flat.
+        for (let col = 0; col < W; col++) {
+          const o = (row * W + col) * 4;
+          buf[o] = 8; buf[o + 1] = 7; buf[o + 2] = 9; buf[o + 3] = 255;
         }
-      const mid = (a.fwd + b.fwd) / 2;
-      if (mid > 11) return;
-      ctx.strokeStyle = `rgba(18,14,10,${Math.min(0.75, 1.0 / (1 + mid * 0.35))})`;
-      ctx.beginPath();
-      ctx.moveTo(W / 2 + (a.side / a.fwd) * fx, half + (H / 2) / a.fwd);
-      ctx.lineTo(W / 2 + (b.side / b.fwd) * fx, half + (H / 2) / b.fwd);
-      ctx.stroke();
-    };
-    const R = 11;
-    for (let gx = Math.floor(x) - R; gx <= Math.floor(x) + R; gx++) {
-      for (let gy = Math.floor(y) - R; gy <= Math.floor(y) + R; gy++) {
-        seg(gx, gy, gx + 1, gy);
-        seg(gx, gy, gx, gy + 1);
+        continue;
+      }
+      const d = (H / 2) / dz;
+      const tex = below ? fl : ce;
+      const tw = tex.width, th = tex.height;
+      const tp = tex.data;
+      const shade = Math.max(0, Math.min(1, 1.25 / (1 + d * 0.45)) * (1 - d / FOG));
+      // World position at column 0 and its per-column step, both at depth d.
+      const sideStep = d / fx;
+      const side0 = -(W / 2) * sideStep;
+      let wx = x + d * cosF - side0 * sinF;
+      let wy = y + d * sinF + side0 * cosF;
+      const stepX = -sideStep * sinF;
+      const stepY = sideStep * cosF;
+      for (let col = 0; col < W; col++) {
+        const o = (row * W + col) * 4;
+        if (shade <= 0.02) {
+          buf[o] = 8; buf[o + 1] = 7; buf[o + 2] = 9;
+        } else {
+          let u = wx % 1; if (u < 0) u += 1;
+          let v = wy % 1; if (v < 0) v += 1;
+          const ti = (((v * th) | 0) * tw + ((u * tw) | 0)) * 4;
+          buf[o] = tp[ti]! * shade;
+          buf[o + 1] = tp[ti + 1]! * shade;
+          buf[o + 2] = tp[ti + 2]! * shade;
+        }
+        buf[o + 3] = 255;
+        wx += stepX;
+        wy += stepY;
       }
     }
+    ctx.putImageData(frame, 0, 0);
 
     // Walls, one ray per column; remember each column's depth for sprites.
     const zbuf = new Float64Array(W);

packages/web/src/fpv/textures.ts

@@ -79,6 +79,34 @@ export function proceduralTextures(): Record<string, HTMLCanvasElement> {
       c.fillRect(h2(i, 1) * TEX, TEX - h2(i, 7) * TEX, w, h2(i, 7) * TEX);
     }
   }),
+  floor: bake((c) => {
+    // Flagstones: a 2x2 of worn slabs per cell, the mortar border carrying
+    // the tile seam so every cell reads as one square of the maze.
+    c.fillStyle = "#3a3226";
+    c.fillRect(0, 0, TEX, TEX);
+    for (let r = 0; r < 2; r++) {
+      for (let q = 0; q < 2; q++) {
+        const jit = 0.8 + 0.3 * h2(r * 3 + 1, q * 7 + 2);
+        c.fillStyle = `rgb(${74 * jit | 0},${64 * jit | 0},${48 * jit | 0})`;
+        c.fillRect(q * (TEX / 2) + 2, r * (TEX / 2) + 2, TEX / 2 - 4, TEX / 2 - 4);
+      }
+    }
+    c.strokeStyle = "rgba(16,12,8,0.9)";
+    c.lineWidth = 3;
+    c.strokeRect(0.5, 0.5, TEX - 1, TEX - 1);
+  }),
+  ceiling: bake((c) => {
+    // Heavy dark slabs overhead, barely catching the torchlight.
+    c.fillStyle = "#161310";
+    c.fillRect(0, 0, TEX, TEX);
+    for (let r = 0; r < 2; r++) {
+      for (let q = 0; q < 2; q++) {
+        const jit = 0.75 + 0.3 * h2(r * 5 + 3, q * 11 + 4);
+        c.fillStyle = `rgb(${34 * jit | 0},${30 * jit | 0},${26 * jit | 0})`;
+        c.fillRect(q * (TEX / 2) + 1, r * (TEX / 2) + 1, TEX / 2 - 2, TEX / 2 - 2);
+      }
+    }
+  }),
   warp: bake((c) => {
     const grad = c.createLinearGradient(0, 0, TEX, TEX);
     grad.addColorStop(0, "#2c1a4e");