From: "Bruce Cohen;;50-662;LP=A;" Subject: Re: We need a new language Date: 6 Feb 91 02:19:51 GMT Organization: Tektronix Inc. In article <15638@milton.u.washington.edu> frerichs@ux1.cso.uiuc.edu (David J Fr erichs) writes: > > Have you used a VR sytem before...? No VR system in existence has a frame > rate that high. (if there is, I will be quite impressed.) > This is not a exact figure, but the VPL system only has > a frame rate of about 8Hz per eye (I have heard it is lower that that even). > Systems I have used have rates higher than that (no numbers allowed) but > still they don't come close to 60Hz (I hope that you are talking about > the frame rates of both eyes, not just one.) > Your statement that one tends to get sick at a low frame rate is false > (IMHO). Please forgive my forwardness if you have experienced this sickness > first hand. Low frame rates only make for choppy movement, not flickering. > It just means that the frame stays in the buffer longer. When you are > doing computer animation, you don't just flash a picture and take it > away, you hold a picture up til the next one is ready. High frame rate > means smoother motion, not less flicker (flicker has to do with the display > hardware frequency). That's true down to some minimum frame rate which depends on just how much interaction the user is trying to do. Below the minimum, you lose the ability to interact effectively with the display. In other words, if you move your head by 20 degrees and it takes more than about a quarter of a second for the view to change, you will not get feedback about the amount of angular change in time to prevent overshooting the angle you wanted. If the delay is too long (depends on the amount of angle and rate of swing) the angular velocity of your head will exceed the maximum acceptable for the feedback loop consisting of your head and the display, and you'll probably go into oscillation. Similar problems occur when you move your hand. I spent *quite* a lot of time dealing with this problem when implementing the 3D input feedback system of the Tektronix 3D terminal / workstation, now departed :-(. It turns out that the best you can do is accumulate motions while the last frame is updating, so at least you don't queue up more frame updates and fall constantly further behind. So you try as hard as you can to make the update fast. -- ------------------------------------------------------------------------ Speaker-to-managers, aka Bruce Cohen, Computer Research Lab email: brucec@tekchips.labs.tek.com Tektronix Laboratories, Tektronix, Inc. phone: (503)627-5241 M/S 50-662, P.O. Box 500, Beaverton, OR 97077