--- slave-rift-base/src/Gfx/Meshes.php	2026-10-31 17:18:00.000000000 +0000
+++ slave-rift-workspace/src/Gfx/Meshes.php	2026-10-31 17:22:31.434288364 +0000
@@ -83,6 +83,42 @@
     }
 
     /** @return float[] */
+    public static function decals(array $decals, string $material): array
+    {
+        $out = [];
+        foreach ($decals as $decal) {
+            if (($decal['material'] ?? '') !== $material) continue;
+            [$x, $y, $z] = $decal['position'];
+            [$nx, $ny, $nz] = $decal['normal'];
+            $halfW = $decal['width'] * 0.5;
+            $halfH = $decal['height'] * 0.5;
+            // Horizontal tangent in the wall plane. The normal is always one of
+            // the four cardinal wall normals in generated modules.
+            $rx = -$nz;
+            $rz = $nx;
+            $offset = 0.012;
+            $cx = $x + $nx * $offset;
+            $cy = $y + $ny * $offset;
+            $cz = $z + $nz * $offset;
+            $leftX = $cx - $rx * $halfW;
+            $leftZ = $cz - $rz * $halfW;
+            $rightX = $cx + $rx * $halfW;
+            $rightZ = $cz + $rz * $halfW;
+            $bottom = $cy - $halfH;
+            $top = $cy + $halfH;
+            $normal = [$nx, $ny, $nz];
+            $color = [1.0, 1.0, 1.0];
+            self::vertex($out, [$leftX, $bottom, $leftZ], $color, $normal, [0.0, 1.0]);
+            self::vertex($out, [$leftX, $top, $leftZ], $color, $normal, [0.0, 0.0]);
+            self::vertex($out, [$rightX, $top, $rightZ], $color, $normal, [1.0, 0.0]);
+            self::vertex($out, [$leftX, $bottom, $leftZ], $color, $normal, [0.0, 1.0]);
+            self::vertex($out, [$rightX, $top, $rightZ], $color, $normal, [1.0, 0.0]);
+            self::vertex($out, [$rightX, $bottom, $rightZ], $color, $normal, [1.0, 1.0]);
+        }
+        return $out;
+    }
+
+    /** @return float[] */
     public static function enemy(string $type): array
     {
         $out = [];
@@ -159,9 +195,9 @@
     }
 
     /** @param float[] $p @param float[] $c @param float[] $n */
-    private static function vertex(array &$out, array $p, array $c, array $n): void
+    private static function vertex(array &$out, array $p, array $c, array $n, ?array $uv = null): void
     {
-        [$u, $v] = self::uv($p, $n);
+        [$u, $v] = $uv ?? self::uv($p, $n);
         array_push($out, $p[0], $p[1], $p[2], $c[0], $c[1], $c[2], $n[0], $n[1], $n[2], $u, $v);
     }