Topic       : TOS - The Operating System
Author      : 
Version     : tos.hyp (December 19, 2008)
Subject     : Programmieren/Atari
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Compiled on : Atari
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View Ref-File8.2.6  The rectangle-list of a window                              TOS

To overcome the problem of windows that overlap each other, the AES 
holds for each window a so-called rectangle-list; when a window is 
partially obscured, GEM divides the visible portion of that window 
into the least possible number of non-overlapping rectangles, the 
details of which are then stored in the rectangle-list. Thus the 
elements of this list form a record of the currently completely 
visible working area of the corresponding window.

To redraw a window (or its contents) one first inquires with the 
function wind_get(WF_FIRSTXYWH) for the first rectangle of the above- 
mentioned list. Then one checks whether this rectangle overlaps with 
the screen area to be redrawn; then and only then one can redraw this 
area with the use of vs_clip.

This method will be continued with all remaining elements of the 
rectangle-list, until the height and the width of a rectangle have the 
value zero.

See also: Clipping   WM_REDRAW   wind_get   wind_update