diff --git a/TODO b/TODO
new file mode 100644
index 0000000..8dddc4d
--- /dev/null
+++ b/TODO
@@ -0,0 +1,4 @@
+portals to other scenes
+collision events
+touch events/interactions
+motion with xr without a controller
diff --git a/protocols/schemas/shapes.prs b/protocols/schemas/shapes.prs
index feb296d..800fbad 100644
--- a/protocols/schemas/shapes.prs
+++ b/protocols/schemas/shapes.prs
@@ -2,7 +2,9 @@ version 1 .
 
 Sprite = <sprite @name string @shape Shape> .
 
-Shape = Sphere / Box / Light / Ground / Scale / Move / Rotate / @many [Shape ...] / Texture / Color / Name / Floor / Nonphysical .
+Shape = Mesh / Light / Scale / Move / Rotate / @many [Shape ...] / Texture / Color / Name / Floor / Nonphysical / CSG .
+
+Mesh = Sphere / Box / Ground .
 
 Sphere = <sphere> .
 Box = <box> .
@@ -33,3 +35,13 @@ Name = <name @base string @shape Shape> .
 Floor = <floor @shape Shape> .
 
 Nonphysical = <nonphysical @shape Shape> .
+
+CSG = <csg @expr CSGExpr> .
+
+CSGExpr =
+/ <mesh @shape Shape>
+/ <subtract @base CSGExpr @more [CSGExpr ...]>
+/ <union @shapes [CSGExpr ...]>
+/ <intersect @shapes [CSGExpr ...]>
+/ <invert @shape CSGExpr>
+.
diff --git a/scene/example.pr b/scene/example.pr
index 2e8614e..0b3ad50 100644
--- a/scene/example.pr
+++ b/scene/example.pr
@@ -3,12 +3,12 @@
 <sprite "ground"
  <texture
   "textures/grass-256x256.jpg"
-  <v 0.1 0.1>
+  <v 0.01 0.01>
   <v 0.0 0.0>
-  <floor <ground <v 30.0 30.0>>>>>
+  <floor <ground <v 300.0 300.0>>>>>
 
 <sprite "box"
- <move <v 6.0 2.5 8.0>
+ <move <v -6.0 1.0 8.0>
   <scale <v 10.0 0.1 10.0>
    <texture "textures/oak-herringbone-5e80fb40b00c9-1200.jpg"
     <v 0.1 0.1>
@@ -17,8 +17,34 @@
     <floor <box>>>>>>
 
 <sprite "box2"
- <move <v -1.0 0.5 3.0>
+ <move <v -500.0 0.5 3.0>
   <floor
-   <color 1.0 0.0 0.0 0.5 <box>>>>>
+   <color 0.0 0.0 1.0 1.0
+    <scale <v 1000.0 1.0 1.0> <box>>>>>>
+
+<sprite "steps"
+ <color 0.0 0.5 0.0
+  <move <v 0.0 0.0 3.5>
+   <scale <v 1.0 1.0 3.0>
+    <texture "textures/oak-herringbone-5e80fb40b00c9-1200.jpg"
+     [
+       <move <v 0.0 0.25 0.0> <box>>
+       <move <v 1.0 0.0 0.0> <box>>
+       <move <v 2.0 -0.25 0.0> <box>>
+     ]>>>>>
+
+<sprite "ball"
+ <move <v 0.0 2.0 3.0>
+  <scale <v 1.0 3.0 1.0>
+   <color 1.0 1.0 0.0
+    <floor
+     <sphere>>>>>>
+
+<sprite "plans"
+ <texture "plans/signal-2022-12-27-125451_002.jpeg"
+  <move <v 0.0 1.0 -10.0>
+   <rotate <v 0.5 0.0 0.0>
+    <scale <v 2.0 2.0 0.1>
+     <box>>>>>>
 
 []
diff --git a/src/engine.ts b/src/engine.ts
index 60e01f9..809638e 100644
--- a/src/engine.ts
+++ b/src/engine.ts
@@ -83,6 +83,7 @@ export async function startEngine(
         camera = new FreeCamera("camera", initialPos, scene);
         camera.minZ = 0.1;
         camera.rotation = initialRotation;
+        camera.speed = 0.5;
         camera.attachControl(canvas, true);
     }
     const sm = xrAvailable ? xr.baseExperience.sessionManager : null;
diff --git a/src/index.ts b/src/index.ts
index cc8535d..1a91702 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -77,7 +77,8 @@ function bootApp(ds: Ref, scene: Scene) {
                         field rotation: Shapes.Vector3 = Shapes.Vector3({ x:0, y:0, z:0 });
 
                         at ds {
-                            on message timer.PeriodicTick(100) => {
+                            const refreshPeriod = Math.floor(1000 / 30);
+                            on message timer.PeriodicTick(refreshPeriod) => {
                                 const camera = scene.cameras[0];
                                 if (camera && camera instanceof TargetCamera) {
                                     const newPosition = Shapes.Vector3(camera.position);
@@ -107,7 +108,7 @@ function bootApp(ds: Ref, scene: Scene) {
                                                     v: Shapes.Vector3({ x: 0, y: rotation.value.y, z: 0 }),
                                                     shape: Shapes.Shape.Scale(Shapes.Scale({
                                                         v: Shapes.Vector3({ x: 0.4, y: 1.4, z: 0.1 }),
-                                                        shape: Shapes.Shape.Box(Shapes.Box()),
+                                                        shape: Shapes.Shape.Mesh(Shapes.Mesh.Box(Shapes.Box())),
                                                     })),
                                                 })),
                                             })),
@@ -115,7 +116,7 @@ function bootApp(ds: Ref, scene: Scene) {
                                                 v: rotation.value,
                                                 shape: Shapes.Shape.Scale(Shapes.Scale({
                                                     v: Shapes.Vector3({ x:0.15, y:0.23, z:0.18 }),
-                                                    shape: Shapes.Shape.Box(Shapes.Box()),
+                                                    shape: Shapes.Shape.Mesh(Shapes.Mesh.Box(Shapes.Box())),
                                                 })),
                                             })),
                                         ]),
diff --git a/src/shapes.ts b/src/shapes.ts
index 7f41b18..371e1a7 100644
--- a/src/shapes.ts
+++ b/src/shapes.ts
@@ -1,5 +1,4 @@
 import {
-    AbstractMesh,
     Color3,
     CSG,
     HemisphericLight,
@@ -123,16 +122,31 @@ function applyCustomizer(m: ShapeTree<Mesh>, c: MeshCustomizer) {
 
 export function build(name: string, scene: Scene, shape: Shapes.Shape, customize: MeshCustomizer): ShapeTree {
     switch (shape._variant) {
-        case "Sphere": {
-            const t = new ShapeTree<Mesh>(scene, shape, MeshBuilder.CreateSphere(name, {}, scene));
-            applyCustomizer(t, customize);
-            return t;
-        }
+        case "Mesh": {
+            const mesh = shape.value;
+            switch (mesh._variant) {
+                case "Sphere": {
+                    const t = new ShapeTree<Mesh>(scene, shape, MeshBuilder.CreateSphere(name, {}, scene));
+                    applyCustomizer(t, customize);
+                    return t;
+                }
 
-        case "Box": {
-            const t = new ShapeTree<Mesh>(scene, shape, MeshBuilder.CreateBox(name, {}, scene));
-            applyCustomizer(t, customize);
-            return t;
+                case "Box": {
+                    const t = new ShapeTree<Mesh>(scene, shape, MeshBuilder.CreateBox(name, {}, scene));
+                    applyCustomizer(t, customize);
+                    return t;
+                }
+
+                case "Ground": {
+                    const v = v2(mesh.value.size);
+                    const t = new ShapeTree(
+                        scene,
+                        shape,
+                        MeshBuilder.CreateGround(name, { width: v.x, height: v.y }, scene));
+                    applyCustomizer(t, customize);
+                    return t;
+                }
+            }
         }
 
         case "Light":
@@ -141,16 +155,6 @@ export function build(name: string, scene: Scene, shape: Shapes.Shape, customize
                 shape,
                 new HemisphericLight(name, v3(shape.value.v), scene));
 
-        case "Ground": {
-            const v = v2(shape.value.size);
-            const t = new ShapeTree(
-                scene,
-                shape,
-                MeshBuilder.CreateGround(name, { width: v.x, height: v.y }, scene));
-            applyCustomizer(t, customize);
-            return t;
-        }
-
         case "Scale": {
             const t = ShapeTree.transform(name, scene, shape);
             t.node.scaling = v3(shape.value.v);
@@ -246,6 +250,10 @@ export function build(name: string, scene: Scene, shape: Shapes.Shape, customize
                 },
             });
 
+        case "CSG": {
+            throw new Error("unimplemented");
+        }
+
         default:
             ((_shape: never) => {
                 console.error('Unsupported shape variant', shape);