Re: LOD calculations
John Rohlf (jrohlf++at++tubes)
Sat, 10 Jun 95 12:15:23 PDT
>
>
>
> I am wondering how channel size affects how Performer calculates LOD range
> for a predefined object with LOD ranges. I have the following information:
>
> >Inside Performer for LOD switching,
> >
> > true range = (defined range) * (Lod Scale) * (Global Lod Scale)
> >
> > defined range is assumed to be for 1280x1024 at 45 Degree FOV
> >
> > Lod Scale is a multiplier calculated from channel size & actual FOV
> /\
> Lod Scale || is what I have my question on...
>
> > Global Lod Scale is a global value per channel that is applied to all
> > LOD's
>
> The part below is the part I'm wondering about, which determines the
> Lod Scale---what are horz and vert on the
> right hand side of this equation??? Are they field of view? I'm assuming that
> xs and ys are the x and y channel size, but I may be wrong on that too.
> Also, is this horz and vert defined recursively, or is that some typo?
horiz, vert are originally the FOVs and xs,ys are the channel's
viewport pixel sizes.
>
> > /* this came from the Performer Team and is how a channel size */
> > /* affects the Lod Calculation */
> > horz = (xs * 0.5f) / pfTan(horz * 0.5f);
> > vert = (ys * 0.5f) / pfTan(vert * 0.5f);
> >
> > max = PF_MAX2(horz, vert);
>
> What is TAN_MPI8?????
>
tan(pi/8) or,
#define TAN_MPI8 .414213562
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on Mon Aug 10 1998 - 17:51:35 PDT