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Asked: 2026-05-12T17:47:40+00:00

I have written a custom control that renders some graphics. The graphics itself is

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I have written a custom control that renders some graphics. The graphics itself is fairly expensive to render but once rendered it rarely changes. The problem I have is that if you move the mouse really fast over the graphics surface it keeps calling the control’s overridden Paint method which then incurs a high CPU penalty:

private void UserControl1_Paint(object sender, PaintEventArgs e)

What techniques could be used to avoid this situation or minimise any unnecessary redrawing since the graphics/image underneath the mouse pointer is not actually changing?

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1 Answer

  1. Editorial Team

    EDIT: After seeing your edit, I can assure you that OnPaint is not called by default when the mouse moves over a control. Something in your code is definitely causing the re-paint, you just don’t see it yet. Perhaps posting some of your code would help us find the problem.

    Are you invalidating your control on MouseMove? That is likely a bad idea, and if you really needed to do it (i.e., you are making a graphics editor or something), you would have to be smart about how large a region was actually re-drawn. So, solution; don’t paint your control in MouseMove.

    Otherwise, I would not expect OnPaint to fire when the mouse moves over the control. You can also just generate the image once and then blt it to the Graphics object until it needs to be re-generated.

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