Re: How to create the Sun?

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Michael T. Jones (mtj++at++babar.asd.sgi.com)
Mon, 6 May 1996 08:26:47 -0700

Nuno adds the comment:
:Since the sphere is simetrical in every axis, wouldn't it be faster to
:make use of a billboard? Defining a circle in a geoSet and adding the
:same emissive yellow proprieties you taught me before.

Could be. Each billboard causes the computation of a rotation. In fact,
the best way to think of a billboard is as a "smart DCS". Now, this
per-frame DCS computation is not free, but neither is the drawing of
the extra polygons for the 3D sphere-based sun. This is one of the
typical performance trade-off scenarios:

 1. general 3d sphere for sun: many polys

 2. 2d disk for sun, with billboard. less polys, rotation computation

 3. 2d quad with sun texture & billboard. just two polys, needs texture.

If you only have one sun (as is common here on earth) you probably can't
even measure the differences between these approaches, but sush types of
considerations are the key activity in making any application run fast.

Michael

Be seeing you, Phone:415.933.1455 Fax:415.965.2658 M/S:8U-590
Michael T. Jones Silicon Graphics, Advanced Systems Division
mtj++at++sgi.com 2011 N. Shoreline Blvd., Mtn. View, CA 94039-7311
                    "Du musst Amboss oder Hammer sein" -- Goethe

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