Drawing laser beams

im no pro on this topic but wouldnt it be best to use a cylinder and stretch it as the beam stretches? just a thought, not sure of how implementable it is

,Matt

-= kill one your a murderer, kill thousands your a conquerer =-

You could make it a triangular shaped cylinder. That way you are rendering only one more quad and the shape is less visible.

That would make it worse, you would see the texture twice!

I wish I Knew how to make one rectangle that always faces the screen yet points in a specified direction...

To make a polygon look at the camera take a look at the billboarding
sample that comes with DX8 SDK.

KaMiKaZe

To get that ''glowing'' look that you see with lasers, use additive blending instead of normal (alpha) blending.

You''ll find it''ll still look okay when rotated too.

so, you're trying to render a beam weapon,
as in from a turret or something to a hit point on the target, the way it was done in freespace (space sim, but should be aplicable to any situation) was the use of one or more single pollys rotated around the center of the beam to face the viewer, so for a similar effect, what you need to know to calculate the points are

the starting point of the beam
the ending point of the beam
and
the veiwers eyeposition in the same frame or reference to the start and end points (it might be easier to have all of these in world coords)

armed with this,
subtract the starting point from the ending point and normalize the result to find the forward vector of the beam,
then for each end point of the beam you,
subtract the eyeposision from the end point your currently checking,
normalize the result and this gives you the right vector of the beam (or that end of it, though it could be the same for both I think),
*now you have the forward vector (fvec) and the right vector (rvec) all you need now is the up vector and you can start ploting verts*
take the crossproduct of the fvec and the rvec and this will give you the upvector, the up vector will be perpenditular to the eyeposition, so all you have to do is scale-add along the uvec and it's negitive by the width of you're beam, assign some apropriate UV coordanants and render with the texture of choice

if you want to look at some code, the freespace source code project forum is right here
http://dynamic4.gamespy.com/~freespace/forums/forumdisplay.php?s=&forumid=50

Bobboau, bringing you products that work... in theory

[edited by - Bobboau on December 17, 2002 5:17:34 AM]