
# Getting Started - Extruding Polygons

## Building the Car
The car is going to be a very simple one. The body will be built using the *extrudePolygon* method. This is another shape that can be built using *MeshBuilder*. The outline of the shape is drawn in the XZ plane, with points in counter-clockwise order and the extrusion is in the Y direction. The origin for the polygon is the zero point on the bottom plane.

The outline for the car consists of an array of vector3 points forming a horizontal base line, a quarter circle for the front, followed by a horizontal base line. The vertical back with be formed by the *extrudePolygon* method as it automatically joins the first and last point.

```javascript
//base
const outline = [
    new BABYLON.Vector3(-0.3, 0, -0.1),
    new BABYLON.Vector3(0.2, 0, -0.1),
]

//curved front
for (let i = 0; i < 20; i++) {
    outline.push(new BABYLON.Vector3(0.2 * Math.cos(i * Math.PI / 40), 0, 0.2 * Math.sin(i * Math.PI / 40) - 0.1));
}

//top
outline.push(new BABYLON.Vector3(0, 0, 0.1));
outline.push(new BABYLON.Vector3(-0.3, 0, 0.1));
```

These and the depth to extrude along Y, give the shape for the car
```javascript
const car = BABYLON.MeshBuilder.ExtrudePolygon("car", {shape: outline, depth: 0.2});
```

<Playground id="#KDPAQ9#10" title="Learning to Extrude" description="Simple demonstration showing the basics of extruding meshes." image="/img/playgroundsAndNMEs/gettingStartedExtrude1.jpg"/>

We form the wheel for the right back position from a cylinder and add it as a child to the car. Then make copies for the right front, left back and left front wheels. This time using *clone* rather than *createInstance* since we can clone a clone. When we clone a wheel its parent is made the parent of the clone.

```javascript
const wheelRB = BABYLON.MeshBuilder.CreateCylinder("wheelRB", {diameter: 0.125, height: 0.05})
wheelRB.parent = car;
wheelRB.position.z = -0.1;
wheelRB.position.x = -0.2;
wheelRB.position.y = 0.035;

wheelRF = wheelRB.clone("wheelRF");
wheelRF.position.x = 0.1;

wheelLB = wheelRB.clone("wheelLB");
wheelLB.position.y = -0.2 - 0.035;

wheelLF = wheelRF.clone("wheelLF");
wheelLF.position.y = -0.2 - 0.035;
```

<Playground id="#KDPAQ9#11" title="Extruding Wheels" description="Expanding on the basics of extruding meshes." image="/img/playgroundsAndNMEs/gettingStartedExtrude2.jpg"/>

Now we will make the car look a bit more like a car using some textures.


## Animating the Village

Our village is not very lively at the moment so let's add some animation. We are still in the early stages of learning Babylon.js and nowhere near adding a Simms family. The parents and children you are about to be introduced to are the silent type and a way of linking together meshes so that changes to a parent mesh are also applied to their children meshes. We are going to animate a very simple car with wheels that are children to the parent car body. Unlike a real car it is the car body that takes the wheels with it. There is one way that our mesh parents and children behave like a real family, the children can act independently of the parent. Good job too as we do not want the car to rotate with the wheels.

Of course you do not have to build an animation of your own, you can import a ready made one and we will show you the basis of importing an animated character and have it move around the village.

Getting Started - Chapter 3 - Mesh Parents

Parents and Children

Further reading

Parents and Pivots

Learn all about parent relationships and pivots in Babylon.js.