Re: [Plib-users] using triangles

[Steve B. <sjb...@ai...>]

Sami Partinen wrote:

> My problem is that, that I have a "space thing", where is two
> ship. They shoot themselfs all the time. So, I need to
> draw laser triangles thousand times in few seconds. For
> some reason, this didn't work:
> 
>   glBegin(GL_TRIANGLES);  // GL_TRIANGLES piirtää kolmioita
> 
>       glColor3f(1.0, 0.0, 0.0);
>       glVertex3f(0.0, 0.0, 0.0);
>       glColor3f(1.0, 1.0, 0.0);
>       glVertex3f(0.0, 20.0, 0.0);
>       glColor3f(1.0, 0.0, 1.0);
>       glVertex3f(20.0, 0.0, 0.0);
>   glEnd();

There could be many reasons for this.

That code may be OK - but perhaps your triangles are being
back-face culled?

Perhaps you haven't disabled texture mapping and the last
polygon that was drawn before this had a transparency
texture.

Perhaps you have the wrong matrix on the stack so those
polygons are being drawn off the edge of the screen or
closer than the near-clip plane.

Perhaps there is a glMaterial loaded with the alpha set
to zero and glColorMaterial is disabled.

Perhaps you have a glScissor or a user-defined clip plane
in the way?

Perhaps these are being drawn behind a previously rendered
translucent polygon and are being Z-culled.

...you see there are too many options for us to diagnose
your problem without a lot more information.

> and propabbly reason is that, that those things don't
> go in correct buffer, and glutSwapB.... can't
> draw it?

Well, that *could* be it - but it's hard to know without
seeing the entire program.
 
> Other way is create object everytime when ship shoot
> another ship, but it doesnt sound very good idea to
> greate "ten thousand" new object in one session?

I agree.  Transitory special effects like that are often
better drawn using raw OpenGL - SSG is better for things
that don't change much like spaceships, planets and little
green men.
 
> Anyway, ship show and move smoothly, so
> that side works well. Just need to draw those
> lasers with some way.

Can you post more of the program - or (preferably) put it
onto a web site somewhere where we could download the sources
and look at them?

If I had to guess, I'd say that disabling backface culling and
texturing would fix your problem...but it's hard to diagnose
this without seeing more code.

----------------------------- Steve Baker -------------------------------
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