Hi,

As a newcomer to OpenGL I’m having difficulty in understanding how co-ordinate systems are specified… I’ve read up a bit about viewports and clipping volumes, etc. but this seems just to make everything more confusing! I think what I’m trying to do would be easier if I could open a window (using GLUT) that could NOT be resized - is this possible? How, for example, can I define each axis as spanning from, say, -1.0 to 2.0, so that the middle of the 3d space is at 0.5, 0.5, 0.5?

What I’m trying to do is position a point on the circumference of a circle (also made up of points) using mouse input. I’ve set up mouse, entry, and motion callbacks in GLUT, but can’t work out how the mouse coordinates returned by GLUT (which are screen co-ordinates as far as I can tell) can be related to the co-ordinates used for describing GL vertices… Can anybody help me with this?

The code I’m using at the moment, if it helps, can be viewed at:

http://www-users.york.ac.uk/~jrm117/opengl/horiz_gui.c

While I’m here, I might as well also ask another question related to this kind of mouse control… I’d like to position the point on the circumference of the circle under mouse control - this would involve working out the angle between zero-degrees on the circumference of the circle and the mouse pointer. Does anyone have any idea how I could achieve this in code?!

Thanks in advance for any help

James