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Editorial Team
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Asked: 2026-06-16T13:12:19+00:00

There is GetRandomRgn( hdc, hrgn, SYSRGN ) to determine window’s system clipping region. When

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There is GetRandomRgn( hdc, hrgn, SYSRGN ) to determine window’s system clipping region.
When my window is partially covered by other windows I get the correct region.

However, if window that covers my window is a tooltip, it’s not subtracted from the region returned by the function.

Any idea why tooltip windows are not excluded and what can I do to exclude them without enumerating all windows myself, determining how they affect my window, etc?

Thank you.

Update: this is on Windows 7 with Aero disabled.

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1 Answer

  1. Editorial Team

    Because tooltips are layered windows. Layered windows do not participate in classical occlusion. (One reason is that they have alpha, so occlusion is not a binary concept.) You didn’t say why you need this information so there’s not much more that can be said beyond “yup.”

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