HOWTO: How to Get Smallest Bounding Rectangle for Drawing Functions

• Microsoft Win32 Application Programming Interface (API), used with:
  • Microsoft Windows NT, versions 3.5, 3.51, 4.0
  • Microsoft Windows 95

SUMMARY

Windows maintains an accumulated bounding rectangle for each application. An application can retrieve this bounding rectangle by calling GetBoundsRect, and it can set this rectangle by calling SetBoundsRect. But this rectangle may not be the smallest bounding rectangle if your drawing functions contain functions doing text output such as TextOut. GDI does not calculate ahead of time how far across the TextOut functions are going to draw. GDI just sets the right side of the bounding rectangle to a large number.

MORE INFORMATION

To get an accurate and smallest bounding rectangle, call LockWindowUpdate and pass the handle of the window to which you are going to draw. Then Windows records the extent of any attempted operations in a bounding rectangle without doing the actual drawing. When the window is unlocked by LockWindowUpdate(NULL), you can either use GetUpdateRect or intercept the rcPaint member of the PAINTSTRUCT in your WM_PAINT message handler to retrieve this smallest bounding rectangle.

Additional query words: 3.50 4.00 GetUpdateRect

Keywords          : kbNTOS350 kbNTOS351 kbNTOS400 kbSDKWin32 kbWinOS95 
Version           : winnt:3.5,3.51,4.0
Platform          : winnt 
Issue type        : kbhowto 

Last Reviewed: June 16, 1999