Babylon.js/src/Behaviors/Cameras/autoRotationBehavior.ts

module BABYLON {
    /**
     * The autoRotation behavior (BABYLON.AutoRotationBehavior) is designed to create a smooth rotation of an ArcRotateCamera when there is no user interaction.
     * @see http://doc.babylonjs.com/how_to/camera_behaviors#autorotation-behavior
     */
    export class AutoRotationBehavior implements Behavior<ArcRotateCamera> {
        /**
         * Gets the name of the behavior.
         */
        public get name(): string {
            return "AutoRotation";
        }

        private _zoomStopsAnimation = false;
        private _idleRotationSpeed = 0.05;
        private _idleRotationWaitTime = 2000;
        private _idleRotationSpinupTime = 2000;

        /**
        * Sets the flag that indicates if user zooming should stop animation.
        */
        public set zoomStopsAnimation(flag: boolean) {
            this._zoomStopsAnimation = flag;
        }

        /**
        * Gets the flag that indicates if user zooming should stop animation.
        */
        public get zoomStopsAnimation(): boolean {
            return this._zoomStopsAnimation;
        }

        /**
        * Sets the default speed at which the camera rotates around the model.
        */
        public set idleRotationSpeed(speed: number) {
            this._idleRotationSpeed = speed;
        }

        /**
        * Gets the default speed at which the camera rotates around the model.
        */
        public get idleRotationSpeed() {
            return this._idleRotationSpeed;
        }

        /**
        * Sets the time (in milliseconds) to wait after user interaction before the camera starts rotating.
        */
        public set idleRotationWaitTime(time: number) {
            this._idleRotationWaitTime = time;
        }

        /**
        * Gets the time (milliseconds) to wait after user interaction before the camera starts rotating.
        */
        public get idleRotationWaitTime() {
            return this._idleRotationWaitTime;
        }

        /**
        * Sets the time (milliseconds) to take to spin up to the full idle rotation speed.
        */
        public set idleRotationSpinupTime(time: number) {
            this._idleRotationSpinupTime = time;
        }

        /**
        * Gets the time (milliseconds) to take to spin up to the full idle rotation speed.
        */
        public get idleRotationSpinupTime() {
            return this._idleRotationSpinupTime;
        }

        /**
         * Gets a value indicating if the camera is currently rotating because of this behavior
         */
        public get rotationInProgress(): boolean {
            return Math.abs(this._cameraRotationSpeed) > 0;
        }

        // Default behavior functions
        private _onPrePointerObservableObserver: Nullable<Observer<PointerInfoPre>>;
        private _onAfterCheckInputsObserver: Nullable<Observer<Camera>>;
        private _attachedCamera: Nullable<ArcRotateCamera>;
        private _isPointerDown = false;
        private _lastFrameTime: Nullable<number> = null;
        private _lastInteractionTime = -Infinity;
        private _cameraRotationSpeed: number = 0;

        /**
         * Initializes the behavior.
         */
        public init(): void {
            // Do notihng
        }

        /**
         * Attaches the behavior to its arc rotate camera.
         * @param camera Defines the camera to attach the behavior to
         */
        public attach(camera: ArcRotateCamera): void {
            this._attachedCamera = camera;
            let scene = this._attachedCamera.getScene();

            this._onPrePointerObservableObserver = scene.onPrePointerObservable.add((pointerInfoPre) => {
                if (pointerInfoPre.type === PointerEventTypes.POINTERDOWN) {
                    this._isPointerDown = true;
                    return;
                }

                if (pointerInfoPre.type === PointerEventTypes.POINTERUP) {
                    this._isPointerDown = false;
                }
            });

            this._onAfterCheckInputsObserver = camera.onAfterCheckInputsObservable.add(() => {
                let now = Tools.Now;
                let dt = 0;
                if (this._lastFrameTime != null) {
                    dt =  now - this._lastFrameTime;
                }
                this._lastFrameTime = now;

                // Stop the animation if there is user interaction and the animation should stop for this interaction
                this._applyUserInteraction();

                let timeToRotation = now - this._lastInteractionTime - this._idleRotationWaitTime;
                let scale = Math.max(Math.min(timeToRotation / (this._idleRotationSpinupTime), 1), 0);
                this._cameraRotationSpeed = this._idleRotationSpeed * scale;

                // Step camera rotation by rotation speed
                if (this._attachedCamera) {
                    this._attachedCamera.alpha -= this._cameraRotationSpeed * (dt / 1000);
                }
            });
        }

        /**
         * Detaches the behavior from its current arc rotate camera.
         */
        public detach(): void {
            if (!this._attachedCamera) {
                return;
            }
            let scene = this._attachedCamera.getScene();

            if (this._onPrePointerObservableObserver) {
                scene.onPrePointerObservable.remove(this._onPrePointerObservableObserver);
            }

            this._attachedCamera.onAfterCheckInputsObservable.remove(this._onAfterCheckInputsObserver);
            this._attachedCamera = null;
        }

        /**
         * Returns true if user is scrolling.
         * @return true if user is scrolling.
         */
        private _userIsZooming(): boolean {
            if (!this._attachedCamera) {
                return false;
            }
            return this._attachedCamera.inertialRadiusOffset !== 0;
        }

        private _lastFrameRadius = 0;
        private _shouldAnimationStopForInteraction(): boolean {
            if (!this._attachedCamera) {
                return false;
            }

            var zoomHasHitLimit = false;
            if (this._lastFrameRadius === this._attachedCamera.radius && this._attachedCamera.inertialRadiusOffset !== 0) {
                zoomHasHitLimit = true;
            }

            // Update the record of previous radius - works as an approx. indicator of hitting radius limits
            this._lastFrameRadius = this._attachedCamera.radius;
            return this._zoomStopsAnimation ? zoomHasHitLimit : this._userIsZooming();
        }

        /**
         *  Applies any current user interaction to the camera. Takes into account maximum alpha rotation.
         */
        private _applyUserInteraction(): void {
            if (this._userIsMoving() && !this._shouldAnimationStopForInteraction()) {
                this._lastInteractionTime = Tools.Now;
            }
        }

        // Tools
        private _userIsMoving(): boolean {
            if (!this._attachedCamera) {
                return false;
            }

            return this._attachedCamera.inertialAlphaOffset !== 0 ||
                this._attachedCamera.inertialBetaOffset !== 0 ||
                this._attachedCamera.inertialRadiusOffset !== 0 ||
                this._attachedCamera.inertialPanningX !== 0 ||
                this._attachedCamera.inertialPanningY !== 0 ||
                this._isPointerDown;
        }
    }
}