Re: [PyOpenGL-Users] Ingame Overlays

[Maciej K. <ma...@dg...>]

On Thu, Jun 22, 2006 at 07:48:37AM +0100, Rowan wrote:
> I am thinking of embarking on a project to create an in-game mp3
> player control. This control will be brought into the foreground of
> the game.
> 
> My question is it possible to overlay or bring to the very foreground
> a graphical control on top of any directx or opengl game, using
> pyopengl?

This is relatively trivial to do in OpenGL in general.  Many games do
something similar for all kinds of "Heads-Up Display".  A good way of thinking
about this is to imagine that your view of the game world comes from a camera
placed in this world.  To create a HUD, or anything else that appears to
overlay the view, imagine affixing a sheet of glass, perpendicular to the
viewing direction, some small fixed distance from the camera lens (say, 3
feet or 1 meter). Wherever you turn the camera, you're always looking through
the same piece of glass.  Then you can start "scribbling" stuff on this piece
of glass, such as current # of points earned, log messages, chat windows, etc.

To implement this your rendering routine usually would look like this:
- first, draw your game world as usual
- reset the projection matrix, preferrably using gluOrtho, and disable depth
  testing (i.e., glDisable(GL_DEPTH)); this allows you to write & draw stuff
  using simple 2D graphics, and turning off depth testing ensures that you
  fully overwrite what's already shown on screen
- now draw your user interface/overlay stuff

Here's a rough snippet from my render code:

  # draw the gameworld as usual
  draw_world()

  # setup the projection for Heads-Up Display
  w, h = get_window_size()
  glMatrixMode(GL_PROJECTION)
  glLoadIdentity()
  glOrtho(0, w, 0, h, 0.1, 1)
  glMatrixMode(GL_MODELVIEW)
  glLoadIdentity()
  glDisable(GL_DEPTH_TEST)

  # draw all the overlay stuff
  draw_hud()
            
Good luck,

-- 
Maciej Kalisiak       mac "at" dgp.toronto.edu       www.dgp.toronto.edu/~mac