Hello, the math involved depends on whether the rectangle is perpendicular to the camera view direction (no rotation needed) and if the projection is either orthographic or perspective and if it is symmetric or not. In either case you must take into account which edges of the rectangle you want to fit with the view edges (in OSG i suppose this is what ProjectionResizePolicy is meant for) if the rectangle aspect ratio (width by height) differ form the camera. Your objectives in the algebra must be a new view matrix and a new projection matrix (but i suppose you knew that already). With this two matrix you can position the camera where you want.
Supposing the simpler case (rectangle is perpendicular to view direction and the symmetric orthographic projection), the center of the rectangle give you the new center of the view matrix. If the camera have perspective projection, make the new frustums near plane be your new rectangle. Once you have the new view matrix and the projection matrix, you can set them to the camera with setViewMatrix and setProjectionMatrix. Of course, this is only a method, you can also orient your math to compute the vector needed to use setViewMatrixAsLookAt. The eye vector will be the rectangle's plane normal, the center can be computed with the projection matrix of the camera and the up vector is just the cross product (or the camera up vector, if it doesn't roll). A good reference of the model of a camera in 3D is Opengl Programmers Guide (official OpenGL guide). OSG Camera class is just a thin wrapper about opengl methods w.r.t. position and orientation. I think this will not help you much if you have problems with the math methods involved but your problem is just such one. Is this is your case (was mine a few months ago), take a good 3D math book (Allan Watts 3D Computer Graphics for example), a heat coffee or tea and a lot of patience until you understand perfectly 3d math algebra, or you will have problems in the future (if you are working with 3d, of course). Please, don't misunderstand my words. I think sooner or later we all have to read "the avoided math chapter"... If you were asking if OSG has some method that can help you, i haven't found one yet, but the right place to start looking for something similar are the camera manipulator classes. Of course they have more algebra than osg methods.. Best regards. Himar.
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