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copied!<p>You can declare a private Image field and save image state to it for use in undo, using <a href="http://www.devlake.com/design-patterns/memento" rel="nofollow">Memento Design Pattern</a> to save and load object "image" state is the best practice, take a loot at it.</p> <p>However instead of one undo/redo operation a better solution is to implement <strong>multi-undo/redo</strong> strategy as the following:</p> <ul> <li>Declare two stacks one for undo and the other for redo:</li> <li>When <strong>undo</strong> pop the action "image" or "image state" from undo stack and push it to the redo stack.</li> <li>When <strong>redo</strong> pop the action "image" or "image state" from redo stack and push it to the undo stack.</li> </ul> <p>Example:</p> <pre><code>private Stack<Image> _undoStack = new Stack<Image>(); private Stack<Image> _redoStack = new Stack<Image>(); private readonly object _undoRedoLocker = new object(); private void Undo() { lock (_undoRedoLocker) { if (_undoStack.Count > 0) { _redoStack.Push(_undoStack.Pop()); //OnUndo(); pictureBox1.Image = _redoStack.Peek(); pictureBox1.Refresh(); } } } private void Redo() { lock (_undoRedoLocker) { if (_redoStack.Count > 0) { _undoStack.Push(_redoStack.Pop()); //OnRedo(); pictureBox1.Image = _undoStack.Peek(); pictureBox1.Refresh(); } } } //And whenever image need to be modified, add it to the undo stack first and then modify it private void UpdateImageData(Action updateImage) { lock (_undoRedoLocker) { _undoStack.Push(pictureBox1.Image);//image); try { //manipulate the image here. updateImage(); } catch { _undoStack.Pop();//because of exception remove the last added frame from stack throw; } } } private void pictureBox1_MouseClick(object sender, EventArgs e) { UpdateImageData(delegate() { 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 } } </code></pre> <ul> <li>Whenever user want to undo "for instance presses Ctrl+Z" on the form just call Undo();</li> <li>Whenever user want to redo on the form just call Redo();</li> </ul> <p>Note: I didn't test the above code but it should be working probably, if you find any issue leave a comment</p>

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