Alejandro Saez (cano++at++silicon.cl)
Tue, 21 Apr 1998 18:45:20 -0400
This could well be a visual effect. But just to make sure... How or who is
updating the viewpoint. Most of the time this is done by giving a trajectory
path and a velocity which combined give the speed vector. Since the velocity
must be calculated by discreet steps during every frame there is usually a
calculation of the form:
Velocity[Km/Hr} --->Velocity[mts/sec] and then,
Velocity[mts/sec]/Frame Rate[frames/sec]=Velocity [mts/frame]
which would give the distance in meters (or any other unit) you must
travel during each frame to get the desired velocity in [mts/sec]. If you
assume constant frame rate then this is just a matter of multiplying current
speed by a pre-calculated constant. But if the frame rate drops down and you
are still assuming it's constant then you'll end up traveling at half the speed
since the above calculation is only done half as many times as it should during
the same period of time. If you were moving at constant 60[mts/sec] then the
above calculation will tell you that at 60Hz you should move 1 meter for each
frame, after 60 frames (1 second at 60Hz) you have move 60 times 1 meter, thus
60 meters/sec. If you suddenly drop down to 30Hz, then after 1 second (30
frames) you have only moved 30 times 1 meter --> 30 mts/sec.
--
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Alejandro Saez
Software Engineer
Silicon Chile S.A.
Avda. Andres Bello 2777, Of. 602
E-mail: asaez++at++silicon.cl Providencia
Phone: +56 (2) 203 3371 Ext. 105 Santiago
Fax: +56 (2) 203 3370 Chile
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This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:57:17 PDT