diff --git a/src/runtime-three/player-collision.ts b/src/runtime-three/player-collision.ts
new file mode 100644
index 00000000..b4e51204
--- /dev/null
+++ b/src/runtime-three/player-collision.ts
@@ -0,0 +1,50 @@
+import type { Vec3 } from "../core/vector";
+
+export type FirstPersonPlayerShape =
+  | {
+      mode: "capsule";
+      radius: number;
+      height: number;
+      eyeHeight: number;
+    }
+  | {
+      mode: "box";
+      size: Vec3;
+      eyeHeight: number;
+    }
+  | {
+      mode: "none";
+      eyeHeight: number;
+    };
+
+export interface ResolvedPlayerMotion {
+  feetPosition: Vec3;
+  grounded: boolean;
+  collidedAxes: {
+    x: boolean;
+    y: boolean;
+    z: boolean;
+  };
+}
+
+export const FIRST_PERSON_PLAYER_SHAPE: FirstPersonPlayerShape = {
+  mode: "capsule",
+  radius: 0.3,
+  height: 1.8,
+  eyeHeight: 1.6
+};
+
+export function getFirstPersonPlayerEyeHeight(shape: FirstPersonPlayerShape): number {
+  return shape.eyeHeight;
+}
+
+export function getFirstPersonPlayerHeight(shape: FirstPersonPlayerShape): number | null {
+  switch (shape.mode) {
+    case "capsule":
+      return shape.height;
+    case "box":
+      return shape.size.y;
+    case "none":
+      return null;
+  }
+}