Hi all,
I'm encountering an inconsistency between OpenGL vertex manipulation
and OSG. It is almost sure that it's my own misuse of OSG so I will
present the issue and be glad to learn. J
I'm trying to force a point in orthographic projection to have a
specific z value.
Suppose z = 0.95
I know the world point is (xw,yw,zw)
So I calculate near/far planes in orthographic projection to be [0,
zw/z]
Then I create the projection matrix to be
osg::Matrix new_proj =
osg::Matrix::ortho(-(width*0.5),width*0.5,-(height*0.5),height*0.5, 0,
zw/z);
osg::Matrix new_view =
osg::Matrix::identity();
The model view matrix is identity.
Now, I create a dummy vertex to check the projection:
osg::Vec3 pt(0,0,zw/z);
osg::Vec3 s = new_proj.preMult(new_view
.preMult(pt));
I would expect s.z() to be 1 or a smaller number but very very close to
one.
What I get is 3. (width x height are 160x120. zw = 800)
When I use the utility function
double x,y,z;
int success = gluProject(pt.x(), pt.y(),
pt.z(),new_view.ptr(), new_proj.ptr(), vp, &x, &y, &z);
z is very close to 1 (0.9997...) as was expected.
Can anyone explain?
Thanks,
Guy L.
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