Subject:
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Re: 3D matrix math question
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Newsgroups:
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lugnet.cad.dev
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Date:
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Sun, 14 Dec 2008 05:48:03 GMT
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Viewed:
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12274 times
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In lugnet.cad.dev, Timothy Gould wrote:
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If I understand correctly you shouldn’t be checking on the projection, only
on the full 3D transformed points. That means you should check after stage
2.5.
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Actually, the projected points are all that I am checking, and that’s how it’s
supposed to work.
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You’ll need the Z value to work out which side things lie on.
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No. The way that conditional lines work is that if the two control points lie
on the same side of the conditional line on the screen (in window coordinates),
then the conditional line should be drawn. If they lie on opposite sides, the
conditional line shouldn’t be drawn. For the purposes of determining this, the
actual conditional line is considered to be infinitely long. The Z values are
irrelevant for making this determination.
Unfortunately, as far as I can tell, the projection matrix doesn’t produce
useful results for points that lie outside the view frustum. But I can’t skip
it entirely, because that would leave out the effects of perspective, which are
necessary in order to get the right results.
--Travis
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Message has 2 Replies:
 | | Re: 3D matrix math question
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| (...) Hmmm... Though I can't quite pin it down I have a suspicion that this has something to do with the spatial reduction cause by projection. What projection matrix are you using? Would a simple solution just be to move the conditional points (...) (16 years ago, 14-Dec-08, to lugnet.cad.dev, FTX)
| | | Re: 3D matrix math question
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| (...) Is there some 'easy' way to determine if the control points are in or out of frustum? Is there any other way to transform points, without considering the frustum (Well, obviously there is at least one, but it's the long way of calculating the (...) (16 years ago, 14-Dec-08, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: 3D matrix math question
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| (...) If I understand correctly you shouldn't be checking on the projection, only on the full 3D transformed points. That means you should check after stage 2.5. You'll need the Z value to work out which side things lie on. Tim (16 years ago, 14-Dec-08, to lugnet.cad.dev, FTX)
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