feat: bees and frogs

engine/math/Mat4.ts

@@ -20,6 +20,26 @@ export namespace Mat4 {
     return out
   }
 
+  /** Model transform T * Ry * S: uniform `scale`, then a yaw rotation about Y,
+   *  then a translation. Built directly in column-major storage (no intermediate
+   *  matmuls) since it runs per mob per frame. A vertex at local +Z ends up
+   *  pointing along world (sin yaw, 0, cos yaw), i.e. the object faces `yaw`. */
+  export function compose(tx: number, ty: number, tz: number, yaw: number, scale: number): Mat4 {
+    const c = Math.cos(yaw)
+    const s = Math.sin(yaw)
+    const out = new Float32Array(16)
+    out[0] = scale * c
+    out[2] = scale * -s
+    out[5] = scale
+    out[8] = scale * s
+    out[10] = scale * c
+    out[12] = tx
+    out[13] = ty
+    out[14] = tz
+    out[15] = 1
+    return out
+  }
+
   /** Right-handed perspective projection (camera looks down -Z). Maps the view
    *  frustum to clip space; the -1 in row 3 copies -z into w, so the later
    *  divide by w is what produces foreshortening. */