Question

I have a image loaded in picturebox.I perform a paint operation on the image, by the mouseclick event.It paints a small rectangular area with black color, when the mouse is clicked at that point.now I want to implement the undo operation for this .When i click a button the last paint operation should be undone.Here is my code for paint operation..

      private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
    {

            rect.Width = 0;
            rect.Height = 0;
            pictureBox1.Invalidate();


            int radius = 10; //Set the number of pixel you want to use here
            //Calculate the numbers based on radius
            int x0 = Math.Max(e.X - (radius / 2), 0),
                y0 = Math.Max(e.Y - (radius / 2), 0),
                x1 = Math.Min(e.X + (radius / 2), pictureBox1.Width),
                y1 = Math.Min(e.Y + (radius / 2), pictureBox1.Height);
            Bitmap bm = pictureBox1.Image as Bitmap; //Get the bitmap (assuming it is stored that way)
            for (int ix = x0; ix < x1; ix++)
            {
                for (int iy = y0; iy < y1; iy++)
                {
                    bm.SetPixel(ix, iy, Color.Black); //Change the pixel color, maybe should be relative to bitmap
                }
            }
            pictureBox1.Refresh(); //Force refresh
          }

Any one please help me how i can undo the last operation performed.

Answer 1

Because you’re working with raster image in memory you cannot just undo the operation. There can be multiple solutions to this:

1. Keep the original image in memory and for each operation keep the drawing parameters: what was drawn, where, which color. When you will need an undo you will just have to repeat all the operation from the first to last (you may also have a control points where you store an intermediate image)
2. After each operation keep the snapshot of the image – this will be very memory consuming. On undo – restore the previous picture in the list.
3. Keep the changed pixels – on each operation analyze the previous image and new one and keep the pixels changes. You will be able to revert to previous by copying those pixels back.