I might be off base here, but if the vertices are in a quad strip, I guess
they should be ordered something like:
0--2--4--6
| /| /| /|
|/ |/ |/ |
1--3--5--7
Then { p0, p1, p2 }, { p2, p3, p4 }, { p4, p5, p6 } will be counter-
clockwise, and { p1, p2, p3 }, { p3, p4, p5 }, { p5, p6, p7 } will be
clockwise. I don't know whether that would affect picking, or why it
would differ between systems. (The algebra for intersecting a ray with
a triangle doesn't care much about the winding order unless back-facing
triangles are explicitly excluded.)
On the other hand, if it's supposed to be a quad strip, but the vertices
aren't ordered correctly, then there might be empty bits between the
triangles, as Carsten's sketch suggests. If the strip is vertical (rather
than horizontal as I sketched above), that might manifest itself as a
left-right difference: both triangles with bases on the right edge and
apexes at the left top and bottom corners, and the left edge "orphaned",
like Carsten's sketch rotated 90 CCW.
-----Original Message-----
From: Carsten Neumann [mailto:[email protected]]
Sent: Wednesday, November 18, 2009 11:45
To: [email protected]
Subject: Re: [Opensg-users] Problem using intersectAction under Windows 32
...
hm, this looks strange, assuming your p1,...,p4 are in counter clockwise
order you are not testing the correct triangles:
p1---p4 p1 p4
| | | \ / |
| | | \ / |
p2---p3 p2---p3 p2---p3
> But when trying to pick, only the right part of the geometry is picked,
> but picking at the left side has no effect.. If we rotate the object,
> the exact opposite occurs..
>
> The strange thing is that the problem does not occurs under linux...
hm, the OS should not make a difference, strange.
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