Re: pfLightpoint alpha

New Message Reply Date view Thread view Subject view Author view

John Rohlf (jrohlf++at++tubes)
Fri, 10 Mar 95 17:28:59 PST

>
>
> The pfLightPoint manpage states:
>
> "pfLPointColor sets the color of light point index in lpoint to clr. The
> actual color displayed depends on light point direction, shape, position,
> and fog. clr specifies red, green, blue and alpha in the range 0.0 to
> 1.0. A pfLightPoint is turned off with an alpha of 0.0 since it will be rendered
> as completely transparent. "
>
> So basically the only way to "delete" lightpoints from an existing
> lightpoint node is to set the alpha values of the unwanted nodes to
> 0.0. I gather that there's no undocumented pfSetNumLPoints() call or
> pfDeleteLPoint() calls hanging around?
>
> If this is so, does Performer send these complete transparent lightpoints to
> the geometry pipeline or not? For example, say I've got 1000 lightpoints and
> that depending on a number of criteria I'd like to display some of them as 1
> pixel and some of them as 3 pixels. If I setup 2 lightpoint nodes each with
> a 1000 point capability, but one with a pfLPointSize of 1.0 and the other
> with a pfLPointSize of 3.0 - to "move" points between the two nodes, the
> alpha values are changed from 1.0 (exists) to 0.0 (doesn't exist). If I
> always render the whole 1000 points in the scene and evenly balance the
> points between the two nodes (i.e. the same point position never appears
> in both nodes) how many points are sent to the pipeline? 1000 or 2000?
>

        All points are sent to the pipeline. The next release of
Performer will replace pfLightPoint with a better (in my opinion)
mechanism called pfLPointState. pfLPointStates are libpr objects
which can be attached to pfGeoStates just like pfMaterials or
pfTextures. Thus, lightpoints are simply PFGS_POINTS pfGeoSets
with an associated pfLPointState. Additional features supplied by
pfLPointStates are:

        - perspective point size
        - CPU or texture-based range attenuation
        - CPU or texture-based punch-through fog
        - similar directionality to pfLightPoints

pfLPointStates gain the indexing capability of pfGeoStates in 2.0 so
you can have different IR/OTW visuals of the same pfGeoSet.

>
> Also, as it's not documented anywhere, maybe somebody at Multigen or SGI
> can answer this... with the PFLP_OVERALL colour mode can you still
> reliably turn off individual points by tweaking the alpha value? Or do
> you have to re-create a pfLightpoint node that doesn't use this colour
> mode?

        You will need to use PER_VERTEX colors to do this.
In general, due to the bugs in PFLP_OVERALL I suggest you always use
PER_VERTEX colors.

New Message Reply Date view Thread view Subject view Author view

This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:51:03 PDT

This message has been cleansed for anti-spam protection. Replace '++at++' in any mail addresses with the '@' symbol.