🔒 Locked

gluUnProject to z=0

Started by JahToasted Jan 17, 2004 at 1:33 AM 0 replies 1.1k views

Original Post

Jan 17, 2004 at 1:33 AM

Ok, this game is mostly 2d. All of the spaceships stay on the z=0 plane. Now I'm trying to use the mouse to tell my little spaceship where to go. So I punch the mouse coordinates into gluUnProject like so:

  gluUnProject ( (double) mouse_x, 
                 (double) mouse_y, 0.0,
                 modelMatrix, projMatrix, viewPort,
                 &x, &y, &z );

And I get back x,y,z. But the z is 1800 (where the camera is) and not 0 like I want. So now I suppose that I need to find out where a vector coming from the camera, passing through the x,y,z from the gluUnProject above, intersects the z=0 plane. How do I do this? Unless of course there's an easier way... Thanks in advance. [edited by - JahToasted on January 17, 2004 2:34:49 AM]

JahToasted

Jan 17, 2004 at 10:42 PM

Nevermind, I figured it out.

For those who have the same problem here is the solution. This is useful if you want to convert mouse coordinates into opengl coordinates:


        //    Position      View       Up Vector
  gluLookAt(mX, mY, mZoom,     mX,mY, 0,     0, 1, 0);       

  glGetDoublev ( GL_MODELVIEW_MATRIX, modelMatrix ) ;
  glGetDoublev ( GL_PROJECTION_MATRIX, projMatrix ) ;
  glGetIntegerv ( GL_VIEWPORT, viewPort ) ;

  gluUnProject ( mouse_x, 
                 screen_height - mouse_y, 
                 0.0 , modelMatrix, projMatrix, viewPort,
                 ≷_x, ≷_y, &z );

  gl_x = mX + (mZoom * (gl_x - mX) / (mZoom - z))) ;
  gl_y = mY + (mZoom * (gl_y - mY) / (mZoom - z))) ;

gl_x and gl_y will be the mouse''s coordinates at z=0. For different values of z I''m guessing this would be what you''d need to do:


  GLdouble gl_z = 100.0 ;
  gl_x = mX + ((mZoom - gl_z) * (gl_x - mX) / (mZoom - gl_z - z))) ;
  gl_y = mY + ((mZoom - gl_z) * (gl_y - mY) / (mZoom - gl_z - z))) ;

Of course that''s only a guess, I haven''t tried it, and I''m not going to since all I needed was the z=0 case.

I hope this helps someone who was struggling like I was.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.