Microsoft KB Archive/83807

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PRB: CreateEllipticRgn and Ellipse Shapes Not Identical

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Q83807

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1
 * Microsoft Win32 Application Programming Interface (API), used with:
 * Microsoft Windows NT Server versions 3.5, 3.51, 4.0
 * Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0
 * Microsoft Windows 95

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SYMPTOMS
When CreateEllipticRgn is used to create a region in the shape of an ellipse and Ellipse is called with the same parameters to draw an ellipse on the screen, the calculated region does not match the drawn ellipse identically.

CAUSE
Ellipse includes the lower-right point of the bounding rectangle in its calculations, while the CreateEllipticRgn function excludes the lower-right point.

RESOLUTION
To draw a filled ellipse on the screen that matches an elliptic region, create the region with CreateEllipticRgn and call FillRgn to fill the region with the currently selected brush.

STATUS
This behavior is by design.

MORE INFORMATION
The region created by the CreateEllipticRgn is slightly smaller than the elliptical area created by Ellipse. Unfortunately, decreasing the width and height of the bounding rectangle by 1 pixel does not solve the problem. Although changing the parameters of the Ellipse API in this way produces a smaller ellipse, the new ellipse does not match the region created with CreateEllipticRgn.

Additional query words: 3.00 3.10 3.50 4.00 win16sdk

Keywords : kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbSDKWin32 kbOSWin95

Issue type : kbprb

Technology : kbAudDeveloper kbSDKSearch kbWin32sSearch kbWin32API kbWinSDKSearch