[Plib-users] RE: How should I use plib?

[Troy Y. <tro...@ho...>]

FROM: Steve Baker
DATE: 08/15/2000 22:28:39
SUBJECT: RE:  [Plib-users] How should I use plib?

Thanks for your response Steve.  I don't know how you
managed to fit all you do into a day but I'm certainly
glad you do.  I really appreciate your input.

Steve Baker wrote:
> Troy Yee wrote:
>> 
>> Q: What is the best way to create a scene/world using plib?
>>    It seems to me that loaders are extremely useful but
>>    what is their impact on one`s ability to render a scene
>>    quickly and efficiently?  Aside from loading a model,
>>    and scaling/rotating/translating it what else must be
>>    done to manage the scene/world (i.e. BSP trees, LOD, etc.)?
>
> Theoretically - you don`t need to do ANYTHING - that`s what
> SSG is good at.
>
> SSG uses whatever the hierarchy of the scene is in the
> model file - and does heirarchical field-of-view checking to
> ensure nothing outside the field of view gets rendered.

> In TuxKart and TuxAQFH, I`ve used comment fields with a magic
> first character to tell the loader to generate certain kinds
> of ssgBranch node that the loader wouldn`t otherwise be able
> to generate.  That`s one way to get LOD nodes into your
> scene.
>
> However, the idea is that you dump the scene into SSG and let
> it worry about all the rendering issues.
>

So one way to use plib is to develop maps/scenes/tiles using
some package that exports to a format for which plib has a loader
(or write a new loader which reproduces the hierarchy of the scene).
Would one expect this to be the most common method of getting
a scene into one's application?

How does one add dynamic objects to the scene?  Just add a
transform node to the root?  Try to find out where in the scene
hierarchy it should be placed?  Probably the former - what is the
impact on rendering?

>> One of the immediate problems with my ocean approach is that
>> the ocean often disappears - it depends on the direction the
>> camera is pointing and where in the scene it is placed.  I`m
>> guessing that it`s getting culled because there are no vertices
>> of the ocean inside the view frustum.
>
> No - that`s not possible.  SSG computes a bounding sphere around
> all the vertices in each leaf node - if any part of the sphere
> lies inside the view frustum, the node will be passed on to OpenGL.
>
> Are you creating the ocean model in code - or loading it via
> one of the SSG loaders?

Hmm...
I'm using ssgLoadAC(), not creating it myself.  After I load the model,
I add it to a transform node, rotate it (I hand built the model in z-is-up
format so I have to undo the rotate that the loader does), then scale
it from unit size to the game board size.  I don't make any other changes
after that. Do I have to force a recalculation of the BSphere in this case?
(I thought cullAndDraw would do a recalc if it was needed).

>> Here`s the worst part (I think) of how I`m realizing this land
>> in the scene... <cringing in anticipation of being bashed about
>> the head>... I`m loading a single instance of a unit sized AC3D
>> cube, scaling the height to match the height of a grid point
>> (by adding model to ssgTransform node) and translating it to
>> the appropriate grid location.  The net result is lots of
>> stretched cubes clustered about.
>
> You certainly need some serious help!

:)

> You should use a triangular mesh I think.

Yes, I knew that but I wanted to generate something I could
look at with a minimum of effort.  Load - scale - move was
much easier than trying to generate a mesh on the fly.

>> How does one deal with being able to warp the
>> camera anywhere on the map though?
>
> Well, it`s *VERY* complex.  <snip>

My choice of the word 'warp' was not the best.  It sounds like
you took it to mean something like 'fly really really really fast'.
I was actually thinking in the X-windows sense of warping a
pointer - an instantaneous move to a new location.  The idea
here is that a user selects a new entity from which to look at
the scene.  This isn't *VERY* complex is it?

I suspect the issue is that the new location could be quite
far away from the current location so the tiles likely wouldn't
be loaded.  I don't imagine that the new tiles can be loaded
quickly enough to satisfy most users or can they?

I'll look at TerraGear.  I suspect I'll be able to get away with
a lot less detail - the simulation will survive with no 3D at all
(but won't be nearly as interesting!).

Thanks again for taking the time to respond,

Troy.