Question

I have a form, which sets these styles in constructor:

this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
this.SetStyle(ControlStyles.UserPaint, true);
this.SetStyle(ControlStyles.ResizeRedraw, true);
this.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);

And I draw some rectangles in Paint event. There are no controls on the form. Hovewer, when I resize the form, there are black strips at right and bottom of the form. Is there any way to get rid of them? I’ve tried everything, listening for WM_ERASEBKGND in WndProc, manually drawing the form on WM_PAINT, implementing custom double buffer, etc. Is there anything else I could try?

I’ve found this:
https://connect.microsoft.com/VisualStudio/feedback/details/522441/custom-resizing-of-system-windows-window-flickers
and it looks like it is a bug in DWM, but I just hope I can do some workaround.

Please note that I must use double buffering, since I want to draw pretty intense graphic presentation in the Paint event. I develop in C# .NET 2.0, Win7.

Status Update 1

I’ve managed to get rid of most of the black stripes by implementing the resize functionality by myself. Hovewer there are still some minor glitches. Is there any way to do resize and paint operation at once? Here is a pseudo-code of what I need to do:

IntPtr hDC;
var size = new Size(250, 200);
IntPtr handle = API.PaintAndResizeBegin(this.Handle /* Form.Handle */,
                                        size.Width, size.Height, out hDC);
using (var g = Graphics.FromHdc(hDC)) {
    this.backBuffer.Render(g, size);
}
API.PaintAndResizeCommit(handle);

Is there any way to implement the above code?

The second solution could be to back-buffer whole form, including non-client area. But how to do that? I don’t want to paint the non-client area by myself, as I want to keep the nice aero effect on Vista/7. Any help will be deeply appreciated.

Status Update 2

It looks like this problem is unsolvable, since it is omnipresent on Windows, in every application. We can just hope that MS will take some inspiration in Mac OS X and will provide appropriate APIs in new Windows.

Answer 1

I’ve found the function which can paint and resize window at the same time – UpdateLayeredWindow.

So now it should be possible to create resizable windows, which do not have any strips while being resized. However, you need to paint the window content yourself, so it is a little inconvenient. But I think that using WPF and UpdateLayeredWindow, there shouldn’t be any problem.

---

Update

Found problems. 🙂 When using UpdateLayeredWindow, you must paint the window’s border yourself. So, if you want standard window painted using UpdateLayeredWindow with nice glass effect in win7, you are screwed.

On Microsft Connect is even a thread about this problem, where Microsoft says it is a bug by design, and if it ever gets fixed, then probably in Win8 or some newer system. So there isn’t much we could do about this.