billboard

hi,
does anyone know how to code a simple billborard ?
I spent all the weekend trying to understand tuts written in C/C++ but couldn't find any way to make a simple billboard in OpenGL using BlitzMax. (i have very poor knowledge in maths & C++)

Huh? Billboard? Do you mean a textured square?

yes, exactly, a textured square (quad) that always faces the camera. i need that to try coding a small particle system using OpenGL.

As far as i know, to make a billboard i would have to know the normal of the quad and then have it match with the normal of the camera. if anyone knows how to do this in blitzMax i would be very happy if he could show me an exemple code or pseudo code.

Have you tried...
here
and
Blitzmax specific Nehe tutorials

thank you very much tonyg for helping here :)
i've already looked through all the nehe samples and it looks like none of them are using billboards (or maybe i missed it)
i'm going to have a look at the samples on codesampler.com and hope i'll be able to do something with.
if i manage to have a working blitzmax code to make a billboard i will post it here :)

There are special articles on nehe.gamedev.net (under articles) that focus on billboard - particle

Perhaps you will find there what you are looking for? :-)

@Dreamora yes first place i checked, but nehe's tut 19 does not use billboards and yeah there is a great article about billboards but eventhough i somehow understand the theory behind billboards i'm having much of a trouble trying to to that in blitzMax (it's not that hard i know).
I then tried to do my particles with ARB_Point_Sprites which is supposed to be faster and easier but it happens to be an extension of OpenGL and i have to call the extension first and i don't know how to do that either.
at the moment i paused working on this till i feel more confortable with vectors (how to calculate,store and use them).
thanks for all your replies :)

You can convert Nehe 19 to use billboards in the following manner:

Make your camera move etc, with keys - putting it's rotation & translation after the loadmatrix & before the loop.

In the loop itself add the lines:
glPushMatrix()
glTranslate(x,y,z)
glRotate(-camx,0.1,0,0) 'reverse rotate what your camera x
glRotate(-camy,0,0.1,0) 'reverse rotate your camera y (if you're doing this)

Modify the 4 lines of triangle strip drawing code stripping the x,y & z parameters (but keeping the signs & replacing z with 0)
i.e. glVertexf(x+0.5,y-0.5,z) becomes glVertexf(0.5,-0.5,0)

after the glEnd()
glPopMatrix()

The basic theory (although there are many ways to do billboards - this is the simplest) is to glPushMatrix(), reverse all your previous camera rotations, draw your object & then glPopMatrix() to put the model view matrix back to its previous state.

There you have it - billboards.

http://www.lighthouse3d.com/opengl/billboarding/

thank you very much salric and Skurcey, i'm going back to coding my particle system as soon as this evening, thanks to your piece of code + other infos i' ve found, now i feel motivated again to give it another go :)