Rob Jenkins (robj++at++barney.reading.sgi.com)
Wed, 24 May 1995 10:36:56 +0100
I don't have details of fog calibrations but man fogvertex gives calculations
of the blend functions for linear and exponential fog.
Using spline fog allows you to specify a set of fog density/distance points a
Catmull-Rom spline interpolation is used to create hardware fog tables from
this fog ramp table - man pfFog gives more details.
NOTE when using spline fog
from man pfFog:
"
PFFOG_PIX_SPLINE is only effective on RealityEngine graphics systems.
The visual quality of per-pixel fogging is influenced by the ratio of the
distances from the eye to the far and the eye to the near clipping
planes. This ratio should be minimized for best results.
"
You may need to set an environment variable ( RE_FOG_MODE ) depending on the
REV of you RM4 boards to get good spline fog - let me know if you want more
details.
also from past experience ( and help from Bob Drebin ) I have found that you
may need to ensure that you have 12 bits per colour component to get best
results from spline fog - it depends on the complexity of the scene 'behind'
the fog:
use getgconfig(GC_BITS_RED) to find the number of bits per colour component.
I can't say if this is more/less accurate than exponential or linear fog
though.
I guess someone may have ( or I could produce ) a long 'runway' polygon with Z
distance markers on to try different fog over it and measure accuracy - I you
have no other response let me know and I'll do this.
Cheers
Rob
-- ________________________________________________________________ Rob Jenkins, Software Support Group, Silicon Graphics UK Ltd. 1530 Arlington Business Park, Theale, Reading, UK, RG7 4SB. tel 01734 257736, fax 01734 257553, email robj++at++reading.sgi.com,
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