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Re: OpenGL- drawing from coordinates

To: REALbasic Games <realbasic-games at lists dot realsoftware dot com>
Subject: Re: OpenGL- drawing from coordinates
From: Fargo Holiday <fargo at rpgportland dot com>
Date: Wed, 27 Sep 2006 12:45:05 -0700
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References: <451A34D6 dot 9060609 at rpgportland dot com> <7B9C1A36-01A2-4320-B69E-DA01B88CBDDD at fireyesoftware dot com> <080F0D9B-B01A-4B81-91A1-DCF1F65CD67B at fireyesoftware dot com>
Ok, that all makes sense. I doubt I'd want to use anything other triangles in production anyway, for any number of reasons, I was just confused over what was happening there.

Thanks again,
Fargo

Asher Dunn wrote:
Another thing: the results for a non-convex polygon are probably device dependent. That is, you will get different things with different OSs, different drivers or different graphics cards. What you're seeing is OpenGL's "best guess" about how to triangulate the polygon. The underlying renderer only deals with triangles, so everything else is converted to triangles before being rendered. It's best to convert things to triangles yourself to avoid unpredictable results. This goes for quads too - while drawing squares using GL_QUADS is easier than drawing squares using GL_TRIANGLES, non-planar quads can produce bad results. Using triangles also avoids the overhead (however small) of triangulating the polygon every frame.

Asher

-------------------------
Asher Dunn
Head Developer, Fireye Software
http://www.fireyesoftware.com/
AIM, Yahoo, MSN: crazedglkid


On Sep 27, 2006, at 3:01 PM, Asher Dunn wrote:

GL_LINE_LOOP draws a line between teach pair of vertices, pairing the first with the last. GL_POLYGON draws a *convex* polygon fitting the passed vertices. You cannot draw a non-convex or self-intersecting polygon, and the results can be messy if you try (as you have seen). I would suggest decomposing the shape into several pieces - maybe a polygon for the center and a triangle for each tip.

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From  Wed 27 Sep 2006 14:05:41 -0600
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Date: Wed, 27 Sep 2006 14:05:41 -0600
From: joe at strout dot net
To: REALbasic Games <realbasic-games at lists dot realsoftware dot com>
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Subject: Re: shadows demo
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On Sep 27, 2006, at 18:05 UTC, Mike Woodworth wrote:

i don't think you ever uploaded it to your server... the link is broken... think you meant http://www.strout.net/files/shadows-demo.zip

Yes, that's what I meant.  Sorry, everyone -- that'll teach me to post
in a hurry!

Best,
- Joe

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Joe Strout -- joe at strout dot net
Verified Express, LLC     "Making the Internet a Better Place"
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