Angus Henderson (angus++at++death.reading.sgi.com)
Tue, 9 Aug 1994 11:54:11 +0100
The idea is based on the fact that it is good to use a PFES_TAG aka
PFCL_MSDEPTH clear. That is because it clears the z-buffer for free with the
assumption that all pixels in the display are covered once with polygon
geometry.
The most efficient way to use your ONYX is to use tag clear and ensure that
the database approximates to a box around the eyepoint. this always results in
the lowest depth complexity at the worst case viewpoint.
Assuming the ground is covered by database geometry at or around z = 0.0
then to use a tag clear the sky must be drawn with a large polygon at the far
clip plane extending from "high up" to z = 0.0 ( or minimum ground height ).
This must be the intention of PFES_SKY_CLEAR except it uses a fast clear
instead of a tag clear.
I don't think Performer 1.2 has pfESkyMode option that does this - it would
be a "PFES_SKY_TAG" i suppose.
What Clive suggested was an upturned bowl that sits around the eyepoint and
represents the sky. the bowl extends down to intersect with the distant terrain
and has the advantage that it can be given a nice horizon and sky texture to
provide more pitch & heading cues when you can't see the ground.
The "skyBox" has travFuncs that turn off lighting and fog etc. and it is set to
be haze coloured at the horizon so you can't see the join. It has a DCS that
keeps it at the eyepoint and is attached to the scene to pick up h,p,r.
It also has an updateTimeOfDay function very similar to that in the perfly
application.
Is this of any interest to you info-performer ?
ANgus
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