Path: utzoo!utgpu!watmath!att!ucbvax!tut.cis.ohio-state.edu!bloom-beacon!AARDVARK.UMD.EDU!jonnyg
From: jonnyg@AARDVARK.UMD.EDU (Jon Greenblatt)
Newsgroups: comp.windows.x
Subject: Re:  Your double repaint problem
Message-ID: <8908302006.AA14200@aardvark.UMD.EDU>
Date: 30 Aug 89 20:06:20 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 43


	The way I handle multiple repaints in one of my projects is the
following.

	1: If this is my first repaint event since the screen was last updated
		I create a region using the x,y,width, and height of
		the area that needs updating.
	   If this is not my first repaint event I add the new area to
		be painted to the original region using XUnionRectWithRegion.
	2: If the eposure count is 0 at this point I then take the regions
		I have collected and make them the clipping region of my
		current graphics context.

Here is a short clip of how the regions are collected. This is somewhat
dependent on my environment as you can see:

LOCAL addclip(Wnd,expose)
XlWindow Wnd;
XExposeEvent *expose;
        {XRectangle rect;
        if (Wnd->clip_count++ == 0)
                Wnd->clip_region = XCreateRegion();
        MAKE_XRECT(rect,expose->x,expose->y,
                        expose->width,expose->height);
        XUnionRectWithRegion(&rect,Wnd->clip_region,
                                   Wnd->clip_region);
        XClearArea(Dpy,Wnd->id,rect.x,rect.y,rect.width,rect.height,0);
        }

Here is where I set up for clipping:

        XSetRegion(Dpy,Wnd->expose_gc->id,
                        Wnd->clip_region);
        XDestroyRegion(Wnd->clip_region);
        Wnd->clip_count = 0;

I use this in my xlisp toolkit. If you would like to see the entire source
it in available VIA anonymous FTP from rover.umd.edu(128.8.2.73) in the
directory pub/xlisp2.0w.tar.Z. The file of interest is osstuff.x11 as it
contains the X11 dependent stuff. Toolkit designers may be interested in
some of my encapsulation methods I used here.

						JonnyG.