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Q114471: INFO: Drawing a Rubber Rectangle

Article: Q114471
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1,95; winnt:3.5,3.51,4.0
Operating System(s): 
Keyword(s): kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbSDKWin32 kbOSWin95
Last Modified: 12-MAY-2001

3.10 4.00 | 3.50 3.51
WINDOWS   | WINDOWS NT
kbgraphic

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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) 
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SUMMARY
=======

Most drawing software uses what is termed a "rubber rectangle". This term is
used to describe the situation where

1. the left mouse button is held down, defining one corner of the rectangle

2. the mouse is dragged and released at the point defining the opposite corner
  of the rectangle

3. the rectangle is drawn while the mouse is being dragged, so that it looks
  like the rectangle is being stretched and contracted, like a rubber band

MORE INFORMATION
================

The key to making this work is in the following call, which should be made in
the WM_LBUTTONDOWN case:

  <CALL>
     SetROP2( hDC, R2_NOT )

On each WM_MOUSEMOVE message, the rectangle is redrawn in its previous position.
Because of the ROP code, the rectangle appears to be erased. The new position
for the rectangle is calculated and then the rectangle is drawn.

Note that Windows will only let you draw in the invalid area of the window if you
use a DC returned from BeginPaint(). If you want to use the DC returned from
BeginPaint(), you must first call InvalidateRect() to specify the region to be
updated.

With the DC returned from GetWindowDC(), Windows will restrict your drawing to
the client and non-client areas. With the hDC returned from CreateDC(), you can
write on the entire display, so you must be careful.

Additional query words: 3.10 4.00

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Keywords          : kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbSDKWin32 kbOSWin95 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWin32sSearch kbWin32API kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1,95; winnt:3.5,3.51,4.0
Issue type        : kbinfo

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