Invert Background Brush

Question

 I need to draw a rectangle and its Fill brush will be the invert of the background. this background may be it will be an Image.

 

how can I do that?

 

 

Answer 1

Unfortunately, currently version of WPF doesn't allow you to directly manipulate the BitmapSource at pixel level, but with the knowledge of this codeproject article and a bit of interop code, you can achieve this with the following helper class:

 

using System;

using System.Windows;

using System.Windows.Media;

using System.Windows.Media.Imaging;

using System.Windows.Interop;

using GdiPlus = System.Drawing;

 

namespace InvertPixelDemo

{

    public static class BitmapSourceHelper

    {

        // The following code is originally from http://www.codeproject.com/cs/media/csharpgraphicfilters11.asp

        private static GdiPlus.Bitmap InvertBitmap(GdiPlus.Bitmap srcBitmap)

        {

            GdiPlus::Bitmap destImage = new System.Drawing.Bitmap(srcBitmap);

            GdiPlus.Imaging.BitmapData bmData = destImage.LockBits(

                new GdiPlus.Rectangle(0, 0, srcBitmap.Width, srcBitmap.Height),

                GdiPlus.Imaging.ImageLockMode.ReadWrite,

                GdiPlus.Imaging.PixelFormat.Format32bppRgb);

 

            int stride = bmData.Stride;

            System.IntPtr Scan0 = bmData.Scan0;

 

            unsafe

            {

                byte* p = (byte*)(void*)Scan0;

 

                int nPadding = stride - srcBitmap.Width * 4;

                int nWidth = srcBitmap.Width * 4;

 

                for (int y = 0; y < srcBitmap.Height; ++y)

                {

                    for (int x = 0; x < nWidth; ++x)

                    {

                        p[0] = (byte)(255 - p[0]);

                        ++p;

                    }

                    p += nPadding;

                }

            }

 

            destImage.UnlockBits(bmData);

            return destImage;

        }

 

        public static BitmapSource ConvertToBitmapSource(GdiPlus::Bitmap gdiPlusBitmap)

        {

            IntPtr hBitmap = gdiPlusBitmap.GetHbitmap();

            return Imaging.CreateBitmapSourceFromHBitmap(hBitmap, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());

        }

 

        public static BitmapSource ConvertToInvertedBitmapSource(GdiPlus::Bitmap gdiPlusBitmap)

        {

            return ConvertToBitmapSource(InvertBitmap(gdiPlusBitmap));

        }

    }

}

 

Only you get the BitmapSource from ConvertToInvertedBitmapSource() method, you can directly feed it into ImageBrush's constructor.

Hope this helps