Hello! I was wondering if someone could help explain the camera's view matrix to me. The reason I ask is that, when I look at it in the debugger, it is not at all what I expected it to be.
Here's what I am doing. Before calling osg::Viewer::run(), I set the camera manipulator, and set its home position, like so: Code: viewer.setCameraManipulator(new osgGA::TrackballManipulator); viewer.getCameraManipulator()->setHomePosition(osg::Vec3d(0.0, 500.0, 30.0), osg::Vec3d(0.0, 480.0, 30.0), osg::Vec3d(0.0, 0.0, 1.0)); As you can probably tell, this should amount to placing the camera at 0,500,30 and then swinging it around 180 degrees on the Z axis, such that we're looking directly down the -Y axis. So if I wanted to create a world matrix for this camera, I would first create a 180 degree z-rotation matrix: -1 0 0 0 0 -1 0 0 0 0 1 0 0 0 0 1 And then I would multiply it against the translation matrix: 1 0 0 0 0 1 0 0 0 0 1 0 0 500 30 1 Which yields: -1 0 0 0 0 -1 0 0 0 0 1 0 0 500 30 1 So if there is a point that is [1,1,1] relative to the camera, multiplying it by this matrix would yield [-1,499,31], which looks to be the correct world-space position. On the other hand, if I wanted to know what the point [-1, 499, 31] is relative to the camera, I would need to know the inverse of the camera's world matrix, which is the view matrix, which happens to be what my question is about. So anyway, when I calculate the inverse of the camera's world matrix, I get: -1 0 0 0 0 -1 0 0 0 0 1 0 0 500 -30 1 Multiplying my world-space vector [-1, 499, 31] by this matrix yields [1, 1, 1], which is what I want. So, I'm satisfied that this is correct. The problem is, when I actually call osg::Camera::getViewMatrix() for this camera, what I get instead is: 1- 0 0 0 0 0 1 0 0 1 0 0 0 -30 -500 1 ..and multiplying [-1, 499, 31] by this yields [1, 1, -1], which is close, but not what I'm looking for (and I suspect it would be way off if I were multiplying with more interesting vectors). The thing is, the scene seems to render properly, and if I call osg::Matrix::getLookAt() on this (seemingly incorrect) view matrix, it gives me the correct values for the eye, center, and up vectors. So I was hoping someone could explain to me why this works the way that it does, perhaps by pointing out an error in my reasoning. I am trying to implement a shader that is similar to shadow mapping, and it's not working, and this is the only step along the way that isn't working as I expected it to. Thanks! Frank Sullivan[/code] ------------------ Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=18302#18302 _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
