plib-users

[Plib-users] Newbie question

[Marco B. <F1...@so...>]

Hi!

I started using PLIB two days ago and I'm porting my space combat
game from the Panard Vision to PLIB because of many reasons.
I like very much PLIB, but I can't still understand something.

Ok my big problem now is this...
My game is a space sim, so I have to draw the Sun and the other
planets, but they MUST NOT be culled! They must be seen from
any distance, so no frustum has to be applied.
How do I get this effect?
I tried with ssgEntity::setTraversalMask(0) but the Sun is not
drawn at all! Have I use some callback?

Please help!

Thanks in advance!

	Bye Bye
	Marco

Re: [Plib-users] Newbie question

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

Marco Bancale wrote:

> I started using PLIB two days ago and I'm porting my space combat
> game from the Panard Vision to PLIB because of many reasons.
> I like very much PLIB, but I can't still understand something.
> 
> Ok my big problem now is this...
> My game is a space sim, so I have to draw the Sun and the other
> planets, but they MUST NOT be culled! They must be seen from
> any distance, so no frustum has to be applied.

I don't understand why you need any kind of special handling.

Just set the far clip plane out to a gazillion miles and draw
sun and planets as appropriately sized spheres at the right
distance.  So long as the eyepoint doesn't ever get too far
from the origin relative to the sizes of the objects that you
are actually interacting with, all should be well.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
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        http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] Newbie question

[Marco B. <F1...@so...>]

Steve Baker wrote:
> 
> I don't understand why you need any kind of special handling.
> 
> Just set the far clip plane out to a gazillion miles and draw
> sun and planets as appropriately sized spheres at the right
> distance.  So long as the eyepoint doesn't ever get too far
> from the origin relative to the sizes of the objects that you
> are actually interacting with, all should be well.
> 

Hi Steve!

Sure, changing the far plane was my first idea, but in that way
all the objects would not be culled (by the far plane) anymore!
Isn't it? So, if I have 100 spaceships around the solar system,
I should see all of them... always. I think this is not much
optimized :).

Am I wrong?

Thanks for the quick reply.

	Bye Bye
	Marco

Re: [Plib-users] Newbie question

[David M. <da...@me...>]

Marco Bancale writes:

 > Sure, changing the far plane was my first idea, but in that way
 > all the objects would not be culled (by the far plane) anymore!
 > Isn't it? So, if I have 100 spaceships around the solar system,
 > I should see all of them... always. I think this is not much
 > optimized :).

You can put the planets in a separate scene graph:

  ssgSetNearFar(1, 100000);
  ssgCullAndDraw(ships_root);
  ssgSetNearFar(1000, 100000000000000);
  ssgCullAndDraw(planets_root);

The problem is that when the ships get close to planets or the sun,
they might not be drawn properly (i.e. the planet will block the ship
when it shouldn't).

As long as you have only 100 ships, you can just put each one under an
ssgRangeSelector to make sure it's not draw when it's too far away.
With ssgRangeSelector, you can use the same near/far plane for
everything and avoid the z-buffer strangeness.


All the best,


David

-- 
David Megginson, da...@me..., http://www.megginson.com/

Re: [Plib-users] Newbie question

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

David Megginson wrote:
> Marco Bancale writes:
> 
>  > Sure, changing the far plane was my first idea, but in that way
>  > all the objects would not be culled (by the far plane) anymore!
>  > Isn't it? So, if I have 100 spaceships around the solar system,
>  > I should see all of them... always. I think this is not much
>  > optimized :).
> 
> You can put the planets in a separate scene graph:
> 
>   ssgSetNearFar(1, 100000);
>   ssgCullAndDraw(ships_root);
>   ssgSetNearFar(1000, 100000000000000);
>   ssgCullAndDraw(planets_root);
> 
> The problem is that when the ships get close to planets or the sun,
> they might not be drawn properly (i.e. the planet will block the ship
> when it shouldn't).

That won't work...the values written into the Z buffer when rendering
the ships would be meaningless after you'd changed the near/far planes
for drawing the planets - so it would be quite possible for a planet
that's a million miles away to occlude a ship that's just one mile away.

There are some Z tricks you can play to avoid that (in principle) - but
this way isn't one of them.

You could draw the planets first, then clear the Z buffer, then draw the
ships...but then a ship would never be occluded by a planet - no matter
what.

> As long as you have only 100 ships, you can just put each one under an
> ssgRangeSelector to make sure it's not draw when it's too far away.
> With ssgRangeSelector, you can use the same near/far plane for
> everything and avoid the z-buffer strangeness.

Yes - that's the 'right' answer.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] Newbie question

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

Marco Bancale wrote:

> Sure, changing the far plane was my first idea, but in that way
> all the objects would not be culled (by the far plane) anymore!

That's desirably though.

> Isn't it? So, if I have 100 spaceships around the solar system,
> I should see all of them... always. I think this is not much
> optimized :).

You should use the level-of-detail mechanism to control the
complexity of those spaceship models as a function of range.

If you make the lowest level of detail be just a single GL_POINT
and turn even that off beyond (say) 50 kilometers, you should
have exactly what you need.

> Am I wrong?

I hope so!

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net