[ bzflag-Bugs-1104614 ] spining around vector such as [1,-1,0] produce bad rendering

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Bugs item #1104614, was opened at 2005-01-18 11:57
Message generated for change (Comment added) made by trepan
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>Category: None
Group: Rendering problems
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Frederic Jolliton (fredcods)
>Assigned to: Dave Rodgers (trepan)
Summary: spining around vector such as [1,-1,0] produce bad rendering

Initial Comment:
When spinning around 1 -1 0 (and probably for a large
subset of vector), object get rendered badly. I guess
that vertices defining face are no more ordered in CCW.

Object example:

arc
        position 0 0 0
        size 1 1 10
        spin 90 1 -1 0
        shift 0 0 4
end

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>Comment By: Dave Rodgers (trepan)
Date: 2005-01-19 12:37

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The problem was the a determinant
should have been used instead of
(m[0][0] * m[1][1] * m[2][2]). The code
has been modified to exit() if such a
condition is found in 2.0.1+, and should
be fixed when the network protocol is
next broken.

(src/game/MeshTransform.cxx / ~line 300)



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Comment By: Frederic Jolliton (fredcods)
Date: 2005-01-18 17:09

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Here is attached a small text to show a counter example
where checking sign of m[0][0]*m[1][1]*m[2][2] may
eventually be wrong.

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Comment By: Frederic Jolliton (fredcods)
Date: 2005-01-18 13:08

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A little more guess (I'm not familiar with transform code,
forgive me if I'm wrong):

By outputing debug info in
src/game/MeshTransform.cxx/MeshTransform::Tool::Tool for
polarity value and boolean result, I see that inverted =
True for all the case where spin give the wrong result.

So, I guess that polarity test may be wrong here for such
case (I don't know if it's the cause or a consequence.)

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Comment By: Frederic Jolliton (fredcods)
Date: 2005-01-18 12:49

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To be more precise (doing more test):

Angle ]-90;90[ are fine.

And spin() in src/game/MeshTransform.cxx (as far I can tell)
seem correct (checked against some other sources.)

Weird. Spining (rotating) should not impact face
"direction". I don't see where the problem is located.

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