Re: Apple video question?

[mjmahon@aol.com (Michael J. Mahon)]

In article <Pine.A41.4.44.0302202055160.86610-100000@zivunix.uni-muenster.de>,
Holger Picker <pickerh@uni-muenster.de> writes:

>On 20 Feb 2003, Dosius wrote:
>
>> Date: 20 Feb 2003 08:32:43 -0800
>> From: Dosius <steve@dosius.zzn.com>
>> Newsgroups: comp.sys.apple2
>> Subject: Re: Apple video question?
>
>> (But the //e had something like the VBL - although AFAIK it worked
>> only on the //e and not even on the //c.  It was fake, however - there
>> was no real VBL. ;))
>Vertical Blank softswitch (AppleIIe, but not Apple//c): yes. Interrupt: no.
>You would have to write a waiting loop like
>blank1:	LDA $c019
>	BPL blank1
>blank2:	LDA $c019
>	BMI blank2
>	...
>which was very time consuming.

Not really--the intent is to complete everything that needs to be done for
the next frame, and then wait until the end of this frame display before
changing the display.  The only time "wasted" is the extra time left over
between your best case frame update and your worst case frame update,
which, in either case, must be less than the time to refresh a frame (or
some integer multiple of frames) in order to produce smooth animation.

In animation, the object is not to go as fast as possible, but to go at
a constant rate.

-michael

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