Rendering Quake 3 maps (opengl).

Rendering Quake 3 maps (opengl).

Post by Steven Haggert » Tue, 29 Aug 2000 04:00:00

Hi all,
    I understand that Q3 uses the glRenderElements() (this has been
mentioned in a number of docs)
to render its meshes. This is all well and good until you find that the Q3
vertex structure is as follows:
(According to the unofficial spec...)

float[3] position  Vertex position.
float[2][2] texcoord  Vertex texture coordinates. 0=surface, 1=lightmap.
float[3] normal  Vertex normal.
ubyte[4] color  Vertex color. RGBA.


glRenderElements is used to hop around the interleaved array plucking
vertices out and rendering them.
glRenderElements is normally used so you dont transform a point more than
once right? The old
shared vertices thing that we've all used. But what is the chance of having
a vertex that shares
position and texture co-ords and vertex normal and colour? Surely zero? Why
not use glDrawArrays
with a few more vertices?

Any thoughts (maybe Kekoa Proudfoot has some ideas?)




Rendering Quake 3 maps (opengl).

Post by Charles E Hardwidg » Wed, 30 Aug 2000 10:48:30

Quack uses glDrawElements. It also falls back to glBegin...End when
glLockArraysEXT is not available. I suspect other trickery is got up to as

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1. Using Quake map coordinates with OpenGL

Help! I am new to 3D programming and OpenGL so forgive me if I am
missing something really obvious or basic. I am trying to make a 1st
person walk through that will use coordinates from a Quake map file. For
simplicity's sake I want to be able to use a map file instead of a bsp
file. I have read the Quake Map Specs but I haven't been able to find an
answer to this question or at least missed it if it was there. The
coordinates are in X,Y, and Z arrays and I have been drawing them
sequentially using a for loop. I'm having a hard time understanding how
with 3 of coordinates you can define 1 face of a cube. I've been working
under the assumption that each row of coordinates defines a face however
I'm not sure where to get the 4th coordinate. The following is a solid
cube from one of the Quake map files that I've been working with.  

( -64 64 64 ) ( 64 64 64 ) ( 64 -64 64 )  
( -64 -64 -64 ) ( 64 -64 -64 ) ( 64 64 -64 )
( -64 64 64 ) ( -64 -64 64 ) ( -64 -64 -64 )  
( 64 64 -64 ) ( 64 -64 -64 ) ( 64 -64 64 )  
( 64 64 64 ) ( -64 64 64 ) ( -64 64 -64 )  
( 64 -64 -64 ) ( -64 -64 -64 ) ( -64 -64 64 )  

If I draw these coordinates sequentially with GL_TRIANGLES I of course
end up with a triangle for each face instead of a square. The faces are
in the right place but incomplete. For simplicity's sake I use a for
loop to cycle through the coordinates.  


I would use GL_QUADS but I can't figure out where to get the 4th
coordinate needed to complete the quad face. Is there a simple formula
based on the 1st 3 coordinates to determine the 4th coordinate or am I
approaching this the wrong way? I would love to find a formula that
would work with any Quake map including complex ones. Any suggestions
would be much appreciated.

Jim Holmquist

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