class CameraViewport extends BABYLON.GUI.Control {
    private _scene: BABYLON.Scene;
    private _engine: BABYLON.Engine;
    private _observer: BABYLON.Observer<BABYLON.Camera>;
    private tmpActiveCameras: BABYLON.Camera[];
    private tmpViewport = new BABYLON.Viewport(0, 0, 1, 1);
    private _isRendering = false;

    constructor(name: string, private _camera: BABYLON.Camera, performanceMode = true) {
        super(name);
        this._scene = _camera.getScene();
        this._engine = this._scene.getEngine();
        this.tmpActiveCameras = [_camera];

        this.onBeforeDrawObservable.addOnce(() => {
            this._observer = this.host.getScene().onAfterCameraRenderObservable.add(() => {
                if (!this._isRendering) {
                    this.renderScene();
                }
            });
        });

    }
    public _draw(context: CanvasRenderingContext2D) {
        context.fillStyle = this.color;
        context.fillRect(this._currentMeasure.left, this._currentMeasure.top, this._currentMeasure.width, this._currentMeasure.height);
    }
    public renderScene() {
        this._isRendering = true;

        let width = this._engine.getRenderWidth();
        let height = this._engine.getRenderHeight();

        let orgViewport = this._camera.viewport;

        this.tmpViewport.x = this._currentMeasure.left / width;
        this.tmpViewport.y = (height - (this._currentMeasure.top + this._currentMeasure.height)) / height;
        this.tmpViewport.width = this._currentMeasure.width / width;
        this.tmpViewport.height = this._currentMeasure.height / height;

        this._camera.viewport = this.tmpViewport;

        let wasAutoClear = this._scene.autoClear;
        this._scene.autoClear = false;

        if (this._scene.activeCameras.length > 1 || this._scene === this.host.getScene()) {
            let orgActiveCameras = this._scene.activeCameras;
            let orgActiveCamera = this._scene.activeCamera;

            this._scene.activeCameras = this.tmpActiveCameras;
            this._scene.activeCamera = this.tmpActiveCameras[0];

            this._scene.render();

            this._scene.activeCameras = orgActiveCameras;
            this._scene.activeCamera = orgActiveCamera;
        } else {
            this._scene.render();
        }
        this._camera.viewport = orgViewport;
        this._scene.autoClear = wasAutoClear;
        this._isRendering = false;
    }
    public dispose() {
        this.host.getScene().onAfterCameraRenderObservable.remove(this._observer);
        super.dispose();
    }
}
(<any>BABYLON.GUI).CameraViewport = CameraViewport;