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Editorial Team
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Asked: 2026-06-10T10:05:48+00:00

From the MSDN documentation: The BeginPaint function validates the entire client area. The ValidateRect

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From the MSDN documentation:

The BeginPaint function validates the entire client area.

The ValidateRect function should not be called if a portion of the
update region must be validated before the next WM_PAINT message is
generated.1

I’ve been programming with Win32 API for years, and I’ve never thought to call the ValidateRect function. A co-worker of mine today pointed that we were missing a call to ValidateRect, which fixed a bug we were having doing some high-speed animation using GDI (I know, an oxymoron)

Can someone tell me whether or not a call to ValidateRect is necessary after a BeginPaint/EndPaint pair? I have seen no documentation at MSDN that sheds light on this, and what documentation and examples I do see suggest that calling ValidateRect is not necessary.

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1 Answer

  1. Editorial Team

    It’s not necessary. BeginPaint is used when you are validating the area because you handled it (painted it) in WM_PAINT.

    ValidateRect is more to “cancel invalidation”, usually after painting directly on the window without WM_PAINT or because something changed and you no longer want to be issued a pending WM_PAINT.

    The fact that it fixed a bug likely means there’s something else going on, and this accidentally fixed it (maybe by reducing the number of WM_PAINT messages?), or wrong observations (for example you changed 2 things but this one got the attention instead of the other which is the actual fix).

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