Hi J-S,
When transforming normals you can't multiple by a full 4x4 matrix as
it'll include the translation component - instead use the
Matrix*::transform3x3(..) methods.
Robert.
On 5/25/07, Jean-Sébastien Guay <[EMAIL PROTECTED]> wrote:
Hello,
I'm having trouble transforming normals for a model into world space.
I have a scene graph which looks like this:
root
/ | \
T1 T2 T3
| | |
G1 G2 G3
Where T1, T2 and T3 are MatrixTransforms and G1, G2 and G3 are geodes.
I need to do some calculations based on the geometry objects' normals,
so I need to transform these in relation to the MatrixTransforms. I
read that the correct way to transform a normal was to multiply it by
the transpose of the inverse of the transformation matrix, so that's
what I attempt to do, but it doesn't give the correct results (the
illumination becomes all garbled, with dark parts in the middle of
light parts).
I'm doing this in a nodeVisitor which is called from the root of the
graph and traverses down to the geodes. Here's the relevant code:
void MyVisitor::apply(osg::Geode& geode)
{
// ...
osg::Matrixd worldTransform =
osg::computeLocalToWorld(this->getNodePath());
osg::Matrixd invWorldTransform;
invWorldTransform.invert(worldTransform);
// Assume the first drawable is an osg::Geometry.
osg::Geometry* object =
dynamic_cast<osg::Geometry*>(geode.getDrawable(0));
const osg::Array* normals = object->getNormalArray();
const osg::Vec3f* normalData = (osg::Vec3f*)normals->getDataPointer();
const unsigned int num_normals = normals->getNumElements();
for (unsigned int n = 0; n < num_normals; ++n)
{
// V' = M * V is the same as V' = V * Mt where Mt is the
// transpose of M.
osg::Vec3 transformed_normal = invWorldTransform * normalData[n];
transformed_normal.normalize();
do_something_with_normal(transformed_normal);
}
// ...
}
I bet other people have done this to death, so I assume I'm going
about it the wrong way. What is it that I'm missing?
Thanks in advance,
J-S
--
______________________________________________________
Jean-Sebastien Guay [EMAIL PROTECTED]
http://whitestar02.webhop.org/
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