Surface 获取触摸点的颜色值

 /// <summary>

        /// Gets the color of a specific pixel.

        /// </summary>

        /// <param name="pt">The point from which to get a color.</param>

        /// <returns>The color of the point.</returns>

        private System.Windows.Media.Color GetPixelColor(InputDevice inputDevice)

        {

            // Translate the input point to bitmap coordinates

            double transformFactor = ColorWheel.Source.Width / ColorWheel.ActualWidth;

            Point inputPoint = inputDevice.GetPosition(ColorWheel);

            Point bitmapPoint = new Point(inputPoint.X * transformFactor, inputPoint.Y * transformFactor);

            // The point is outside the color wheel. Return black.

            if (bitmapPoint.X < 0 || bitmapPoint.X >= ColorWheel.Source.Width ||

                bitmapPoint.Y < 0 || bitmapPoint.Y >= ColorWheel.Source.Height)

            {

                return Colors.Black;

            }

            // The point is inside the color wheel. Find the color at the point.

            CroppedBitmap cb = new CroppedBitmap(ColorWheel.Source as BitmapSource, new Int32Rect((int)bitmapPoint.X, (int)bitmapPoint.Y, 1, 1));

            byte[] pixels = new byte[4];

            cb.CopyPixels(pixels, 4, 0);

            return Color.FromRgb(pixels[2], pixels[1], pixels[0]);

        }