Re: Alternative Orientation Systems

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Michael Jones (mtj++at++babar)
Wed, 4 Jan 1995 17:45:34 -0800

On Jan 4, 5:03pm, Allan Schaffer wrote:
> Subject: Re: Alternative Orientation Systems
:On Jan 4, 6:21pm, Michael J. Smith wrote:
:> Has there been any attention to allowing the use of Quaternians in the
:> next release of Performer? And if so, will they be instead of Euler
:> Angles or in addition to them? Using quaternians in my application would
:> be more efficient, but needing to change to Euler Angles or a Rotation
:> Matrix from the quaternian each frame might be a large performance hit.
:> What is the Performer Groups position on this subject? (I really mean the
:> Performer library programmers, but general responses are certainly welcome)
:
:mtj has added a bevy of quaternion operators to the Performer math
:library for 2.0 -- I'll append a preliminary API listing below:

Thanks, Allan. If you're a quaternion fan, you'll note that most of the
functions implemented are taken directly from the various publications
of the Reigning Quaternion God, Ken Shoemake.

These are all implemented as macros as well as functions, and the
compiler seems to optimize the code for the complicated operators
very efficiently.

If you've seen the Walt Disney Imagineering Labs "Aladdin Attraction" at
EPCOT Center or at SIGGRAPH 1994, then you saw IRIS Performer
quaternions in action. They're used to extrapolate the viewer's head
position forward in time to minimize perceived latency, as explained
in SIGGRAPH Technical Course #14.

Internally, Performer uses matrices since this is what the hardware
uses and we seek designs that fit the physical machine. If you have
hundreds of quaternions to update per frame at high frame rates, you
may well have trouble with your application process time.

Michael.

-- 


Be seeing you,      Phone:415.390.1455  Fax:415.390.2658 M/S:8U-590
Michael T. Jones    Silicon Graphics, Advanced Graphics Division
mtj++at++sgi.com         2011 N. Shoreline Blvd., Mtn. View, CA 94039-7311

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