xna 触控操作备忘

 private void HandleInput()
        {
            while (TouchPanel.IsGestureAvailable)
            {
                GestureSample gestureSample = TouchPanel.ReadGesture();
                switch (gestureSample.GestureType)
                {
                    case GestureType.FreeDrag:
                        rotationXAmount += gestureSample.Delta.X;
                        rotationYAmount -= gestureSample.Delta.Y;
                        break;

                    case GestureType.Pinch:
                        float gestureValue = 0;
                        float minFOV = 60;
                        float maxFOV = 30;
                        float gestureLengthToZoomScale = 10;

                        Vector2 gestureDiff = gestureSample.Position - gestureSample.Position2;
                        gestureValue = gestureDiff.Length() / gestureLengthToZoomScale;

                        if (null != prevLength) // Skip the first pinch event
                            cameraFOV -= gestureValue - prevLength.Value;

                        cameraFOV = MathHelper.Clamp(cameraFOV, maxFOV, minFOV);

                        prevLength = gestureValue;
                        break;

                    case GestureType.PinchComplete:
                        prevLength = null;
                        break;
                    default:
                        break;
                }
            }
        }