Re: Warping an image with a Bezier Path
Re: Warping an image with a Bezier Path
- Subject: Re: Warping an image with a Bezier Path
- From: "Peter Sichel" <email@hidden>
- Date: Mon, 20 Jan 2003 11:22:25 -0500
>
On Saturday, January 18, 2003, at 08:24 PM, David Remahl wrote:
>
>
> Why do you need a refresh rate of "between 80 and 160" Hz? The screen
>
> will not refresh that frequently, so you wouldn't get anything more
>
> once you exceeded the refresh rate of the display.
>
>
After thinking about it a bit more, I realize now that it doesn't need
>
to be that large but rather around half. 40-60 frames should be fine.
>
I'm going for absolute fluidness, but thinking about what you said and
>
realizing that the display will only be short lived made me realize
>
that "fluidness" is relative.
This is actually more subtle than it appears. In order to do "smooth"
animation, you need to update the image within a single frame time. As
you approach 40-60 frames/second, many folks have noticed the animation
becomes less jerky, but it doesn't become perfectly smooth until you match
or exceed the refresh rate.
For years, most North American CRTs refreshed at 60Hz to minimize power
supply interference (European CRTs used 50Hz for the same reason).
A significant fraction of the population can perceive flicker
at 50 or 60Hz, so quality multi-scan monitors started upping the refresh
rate about 10 years ago. As you approach 70-80 Hz, very few people
still perceive flicker. Higher end multi-scan monitors may refresh
as fast as 80 Hz. Few if any exceed this.
Digital LCDs don't have the flicker problem so can use slower refresh
rates, but seem to have settled at 60 Hz for North America. Some
digital video cameras are now advertising they can capture video
at 24 fps to match the softer quality of film.
If you want the smoothest possible animation, you should tie your screen
updates to the actual screen refresh rate (vertical interrupt). Mac OS X
goes to some length to support this by buffering images so it can apply
changes at just the right time. As long as you don't bypass this, doing
80 frames per second (during motion) provides the best possible smoothness,
but even slower rates may look fine. If you go directly to the frame
buffer, you'll need 50-80 fps tied to the screen refresh interrupt.
- Peter
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