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From: haitex@pnet01.cts.com (Wade Bickel)
Newsgroups: comp.sys.amiga
Subject: Re: Window Clipping
Message-ID: <2439@crash.cts.com>
Date: 29 Jan 88 01:36:11 GMT
Sender: news@crash.cts.com
Organization: People-Net [pnet01], El Cajon CA
Lines: 46


bmacintyre@watsol.waterloo.edu (Blair MacIntyre) writes:
>
>I have recently started a three-d fly-down-the-tunnel type game ( for
>the fun of it ).  As anyone who has ever done three-d anything knows,
>this requires a lot of line clipping after the three to two-d
>transformation.  I was under the impression that the layers library
>would handle this, but ...
>  when I get line that go very far off screen, the line drawing routines
>behave very strangly ( I first thought it was the program, but when
>I wrote my own clipping routine, everything started working ).
>The strange behaviour was as follows:
> - draw a line from point a to point b, both onscreen.  ok.
> - draw a line from point c to point b, with point c far of to the
>   lower left of the screen ( ie. large +y, large -x ).
>   - the line drawn:
>     - does not connect with point b.  It connects corrently in the
>       x direction, but they values are off.
>     - is not even a line.  The result is a jagged series of vertical and
>       sloped connected line segments.
>
>Anyone seen anything like this?  Is the layers library supposed to handle
>this offscreen clipping?  Or, if I have to continue to clip myself, does
>anyone have a very efficient clipping algorithm?
>
>Help!!

        If you are calculatating perspectives, I recently posted an article
to comp.sys.graphics on this topic.

        Basically, I recommend that you do your own clipping.  First clip in
z before translating from 3-D to 2-D.  Then translate to 2-d, and then clip
in x and y.  X and y clipping tends to be a special case which can be
optimized according to needs.

        I tryed using the Layers Lib, but it seemed to do more of some things
and not enough of others for my needs.

                                                        Thanks,


                                                                Wade.

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