
## How to use Multi-Views

Babylon.js can render multiple views of the same scene.

## Active cameras

A scene has an [activeCamera](/typedoc/classes/babylon.scene#activecamera) property to define the point of view. But you can define many active cameras using code like this:

```javascript
scene.activeCameras.push(camera);
scene.activeCameras.push(camera2);
```

## Viewports

If you want to use many cameras, you will need to specify a viewport for each camera:

```javascript
camera.viewport = new BABYLON.Viewport(0.5, 0, 0.5, 1.0);
camera2.viewport = new BABYLON.Viewport(0, 0, 0.5, 1.0);
```

A viewport is defined by the following constructor:

```javascript
BABYLON.Viewport = function (x, y, width, height);
```

where x, y, are the lower lefthand corner of the viewport followed by its width and height. Values for x, y, width, and height are numbers between 0 and 1 representing the fraction of the screen width and height, respectively.

<Playground id="#4JXV32" title="Viewport Example" description="A simple example of constructing a viewport." image="/img/playgroundsAndNMEs/divingDeeperMultiviews3.jpg"/>



# How to use Layer Masks and Multi-Camera Textures

## Different meshes for multiple cameras using layer masks

A `layerMask` is a number assigned to each mesh and camera. It is used at the bit level to indicate whether lights and cameras should shine-upon or show the mesh. The default value, 0x0FFFFFFF, will cause the mesh to be illuminated and shown by any stock light and camera.

The feature is used primarily when multiple cameras are active at the same time. If you wish to have a mesh that is always visible on the screen and pickable, e.g. a button, you might add a second camera and light to the scene to exclusively show and light it.

You'll need the 2nd camera to ONLY see the button. The button should also only be visible once.

Notice that the default `layerMask` starts with the first 4 bits being 0, or off. If the 2nd camera and button were to both have a `layerMask` with one of the 4 values below, then the 2nd camera would only see the button:

- 0x10000000
- 0x20000000
- 0x40000000
- 0x80000000

It should also be noted that a mesh with a `layerMask` of 0, can never be seen by anyone. This might be good for hiding things.

To setup for multi-cameras:

```javascript
if (scene.activeCameras.length === 0){
    scene.activeCameras.push(scene.activeCamera);
}
var secondCamera = new Babylon.Camera(...);
secondCamera.layerMask = 0x10000000;
scene.activeCameras.push(secondCamera);

var Button = new BABYLON.Mesh(...);
Button.layerMask = 0x10000000;
```

## Lights

Unless the material of the meshes for the 2nd camera is purely emissive, this still leaves any light for the button illuminating all the other meshes, and other lights in the scene illuminating the button. To keep scene lights from illuminating the button, loop through the existing lights, and set the excludeWithLayerMask value:

```javascript
for (var i = scene.lights.length - 1; i >= 0; i--) {
  scene.lights[i].excludeWithLayerMask = 0x10000000;
}
```

Then make the "button" light:

```javascript
var light = new BABYLON.Light(...);
light.includeOnlyWithLayerMask = 0x10000000;
```

Finally, if there may be more lights generated later, you can register a call-back when a light is added:

```javascript
scene.onNewLightAdded = onNewLight;
```

This could be:

```javascript
onNewLight = function (newLight, positionInArray, scene) {
  newLight.excludeWithLayerMask = 0x10000000;
};
```

## Gun Sight Crosshair Example

Here is a simple example of using a 2nd orthographic camera that shows a gun sight. To keep it simple, emissive material was used to avoid lighting it. Just copy and paste it into any scene, then call it. The `layerMask` chosen also allows Babylon's Dialog extension to inter-operate. Perhaps these could be combined to do a heads-up tank sight with a rangefinder.

A commercial-quality implementation would probably not use `CreateBox()`, since it creates depth faces that cannot be seen straight-on anyway. It should also take into account a window size change unless it is a tablet app.

```javascript
function addGunSight(scene) {
  if (scene.activeCameras.length === 0) {
    scene.activeCameras.push(scene.activeCamera);
  }
  var secondCamera = new BABYLON.FreeCamera("GunSightCamera", new BABYLON.Vector3(0, 0, -50), scene);
  secondCamera.mode = BABYLON.Camera.ORTHOGRAPHIC_CAMERA;
  secondCamera.layerMask = 0x20000000;
  scene.activeCameras.push(secondCamera);

  meshes = [];
  var h = 250;
  var w = 250;

  var y = BABYLON.Mesh.CreateBox("y", h * 0.2, scene);
  y.scaling = new BABYLON.Vector3(0.05, 1, 1);
  y.position = new BABYLON.Vector3(0, 0, 0);
  meshes.push(y);

  var x = BABYLON.Mesh.CreateBox("x", h * 0.2, scene);
  x.scaling = new BABYLON.Vector3(1, 0.05, 1);
  x.position = new BABYLON.Vector3(0, 0, 0);
  meshes.push(x);

  var lineTop = BABYLON.Mesh.CreateBox("lineTop", w * 0.8, scene);
  lineTop.scaling = new BABYLON.Vector3(1, 0.005, 1);
  lineTop.position = new BABYLON.Vector3(0, h * 0.5, 0);
  meshes.push(lineTop);

  var lineBottom = BABYLON.Mesh.CreateBox("lineBottom", w * 0.8, scene);
  lineBottom.scaling = new BABYLON.Vector3(1, 0.005, 1);
  lineBottom.position = new BABYLON.Vector3(0, h * -0.5, 0);
  meshes.push(lineBottom);

  var lineLeft = BABYLON.Mesh.CreateBox("lineLeft", h, scene);
  lineLeft.scaling = new BABYLON.Vector3(0.01, 1, 1);
  lineLeft.position = new BABYLON.Vector3(w * -0.4, 0, 0);
  meshes.push(lineLeft);

  var lineRight = BABYLON.Mesh.CreateBox("lineRight", h, scene);
  lineRight.scaling = new BABYLON.Vector3(0.01, 1, 1);
  lineRight.position = new BABYLON.Vector3(w * 0.4, 0, 0);
  meshes.push(lineRight);

  var gunSight = BABYLON.Mesh.MergeMeshes(meshes);
  gunSight.name = "gunSight";
  gunSight.layerMask = 0x20000000;
  gunSight.freezeWorldMatrix();

  var mat = new BABYLON.StandardMaterial("emissive mat", scene);
  mat.checkReadyOnlyOnce = true;
  mat.emissiveColor = new BABYLON.Color3(0, 1, 0);

  gunSight.material = mat;
}
```

See it in action here: <Playground id="#JU1DZP" title="Gun Sight Crosshair Example" description="A simple example of creating a gun sight crosshair using layer masks and two cameras." image="/img/playgroundsAndNMEs/divingDeeperLayerMasks1.jpg" isMain={true} category="Cameras"/>

Using the information here and combining it with the viewport information from the previous [section](/features/featuresDeepDive/cameras/multiViewsPart2), we can create a more complex example that includes the option to omit meshes from specific cameras.

<Playground id="#L92PHY#217" title="Picture in Picture Visual Camera" description="Using layer masks and viewports, show a visual representation of camera movement." image="/img/playgroundsAndNMEs/pipcamera.png" isMain={true} category="Cameras"/>



# How to use Multiview

## Introduction

The [WebGL Multiview extension](https://www.khronos.org/registry/webgl/extensions/OVR_multiview2/) allows rendering multiple views (eg. each eye for VR scenarios) in a single render pass. This can make rendering around 1.5 to 2.0 times faster.

Multiview is not currently supported in all browsers. If it is supported, the multiview capability should be present.

```javascript
scene.getEngine().getCaps().multiview;
```

**Note:** Multiview rendering renders to a texture array instead of a standard texture. This may cause unexpected issues when applying postprocessing with custom shaders, effects, or postprocessing (_e.g._, the highlight layer will have no effect).

## Using with VRExperienceHelper

Multiview can be enabled by setting the `useMultiview` option to `true`.

```javascript
scene.createDefaultVRExperience({ useMultiview: true });
```

<Playground id="#SRV2A0" title="VR Experience Multiview Example" description="A simple example of using multiviews for a VR experience." image="/img/playgroundsAndNMEs/divingDeeperMultiviews1.jpg"/>

## Using with VRDeviceOrientationFreeCamera to display on the screen

Enable through the option in the [VRCameraMetrics](/typedoc/classes/babylon.vrcamerametrics) object:

```javascript
// Enable multiview
var multiviewMetrics = BABYLON.VRCameraMetrics.GetDefault();
multiviewMetrics.multiviewEnabled = true;
// Create camera
var multiviewCamera = new BABYLON.VRDeviceOrientationFreeCamera("", new BABYLON.Vector3(-10, 5, 0), scene, undefined, multiviewMetrics);
```

<Playground id="#EZDZZV" title="VRDeviceOrientationFreeCamera Multiview Example" description="A simple example of using multiviews to create a VRDeviceOrientationFreeCamera." image="/img/playgroundsAndNMEs/divingDeeperMultiviews2.jpg"/>


MultiViews Part 2

How to use Multi-Views

Active cameras

Viewports