Bilboard question

Two ways.

1. This one is usually used for particles. Knowing particle position and size: transform position into the camera space and create four points using radius (in camera space):

V - pos; R - radius.
VecMatMul( &V, &viewMatrix );
vertex[0] = Vec( V.x - R, V.y - R, V.z );
vertex[1] = Vec( V.x + R, V.y - R, V.z );
vertex[2] = Vec( V.x + R, V.y + R, V.z );
vertex[3] = Vec( V.x - R, V.y + R, V.z );
 

2. Classic "billboard" method:
You need to create billboard matrix. It works almost like createion of "look at" view matrix:

zAxis = billboardPos - cameraPos;
yAxis = Vec( 0, 1, 0 );
xAxis = VecCross( yAxis, zAxis );
 

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Salut!
Meduzza

Or you could try this :

Get your current model view matrix from OpenGL.
glGetFloatv(GL_MODELVIEW_MATRIX, mat)

Take the transpose of that matrix and store it.
tmat = mat.Transpose().

Create two vectors, x and y, and set them as follows using the transposed matrix.
x.Set(tmat[0], tmat[1], tmat[2]);
y.Set(tmat[4], tmat[5], tmat[6]);

x is a vector that points right and y is a vector that points up. With these two vectors you can easily construct triangles that will always face the camera

Nate Miller
http://nate.scuzzy.net

Thanks for you answers, now I''ve everything I need to de it :p .
It''s for a particles engine, you''ll find the current version on my web page, and as soon as bilboard will be coded I''ll update it.
Thanks again guys.
Julien

My Web Page