Question about perspective

glOrtho() is 2D drawing mode. All coordinates are pixel based.

Its good for drawing a crosshair and HUD in a game or 3D Engine.

[edited by - snisarenko on December 30, 2002 6:47:42 PM]

with glOrtho() you get orthogonal projection, e.g. the x, y and z coordinates are independently scaled/biased, only x and y coordinates are used to compute screen x/y coordinates - use it if you want to do some 2D stuff.
with glFrustum() you get perspective projection similar to the real-world to eye or real-world to film projection in a camera.

gluPerspective is just a glu routine to make life easier - instead of specifying right, left, top, bottom of the screen on the near plane you can specify the aspect ratio and the field-of-view angle; you don''t need gluPerspective, you can do the same things with glFrustum (actually glFrustum can set up projections which can''t be set up with gluPerspective, but I think you won''t need them).

GA