   Can someone help me create a proper perspective matrix?
  Hello. Basically, I have a situation where the person is not going to be sitting directly in front of the screen, but rather off to the side, viewing it at an angle. Here is a top-down view: So, the person would be facing 'up' in this image (although I'm not sure how much that matters).What I'd like to do is set up my projection matrix so that things look correct from this person's point of view. I basically want the TV screen to look like a window into the game world. I guess what I'm wondering is, if I have the measurements of where the person is sitting in relation to the TV, can I use them to construct a perspective matrix that represents the sort of skewed frustum like the red one in the image?I'm using OpenGL, incidentally.   
  I think you can make it work if you use something like what's described here: http://msdn.microsoft.com/en-us/library/bb205354%28VS.85%29.aspx. You'll just need to do a little trig to figure out the extents of the far clipping plane based on the angle.   ;  So would this be a proper way to visualize it, i.e. with the coordinate space oriented such that the x-axis is perpendicular to the screen, and the top/left/bottom/right coords are the corners of the far plane?;  Yes, exactly. With that orientation you just need to figure out the X values of the two far corners, as well as the Y values. Then you can build your off-center projection.   