Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ulowell!m2c!applix!scott
From: scott@applix.UUCP (Scott Evernden)
Newsgroups: comp.sys.amiga.tech
Subject: Re: ClipRect help wanted
Message-ID: <911@applix.UUCP>
Date: 26 Feb 89 06:53:26 GMT
References: <5379@abo.fi>
Reply-To: scott@applix.UUCP (Scott Evernden)
Organization: APPLiX Inc., Westboro MA
Lines: 42

In article <5379@abo.fi> rosenbergr@abo.fi (Robin Rosenberg, Computer Science, ]bo Akademi) writes:
>A simple question: What is the best way of doing clipping. I.e
>I would like to render some text and images into a part of a window. If
>the object goes outside the required borders (a rectangle) I want that part
>chopped of. I know the ROMS have a InstallClipRect() function but how do
>I use it?
>Could anyone give me an example of how to do this the right way?

Sure.  It's really not too hard...

As part of your init code do:

	struct Library *LayersBase;
	struct Region *region;

	LayersBase = OpenLibrary("layers.library", 0L);
	region = NewRegion();

Then, when you want clipping within (xmin,ymin)-(xmax,ymax):

	struct Rectangle rect;

	rect.MinX = minx;
	rect.MinY = miny;
	rect.MaxX = maxx;
	rect.MaxY = maxy;

	ClearRegion(region);
	OrRectRegion(region, &rect);
	InstallClipRegion(window->RPort->Layer, region);

There are lots of region operations, and you can create clip
areas that are not necessarily rectangular by using combinations
of And/Or/XorRectRegion() and -RegionRegion().

Finally, at cleanup time:

	DisposeRegion(region);
	InstallClipRegion(window->RPort->Layer, (struct Region *) NULL);
	CloseLibrary(LayersBase);

-scott