🚀 go-pugleaf

In article <1992Dec17.144044.18199@westminster.ac.uk> fkpec@westminster.ac.uk (Liaket Ali) writes:
>A question (hypothetical) related to Game timing...
>
>I have an AMIGA 500 and will soon be getting a 1200 which is a faster computer.
>The game that I'm currently writing runs at 10 frames per second on the A500.
>However, I would like the game to run at 20fps on the A1200 but be smoother.
>This means that it will not zoom past at twice the speed but instead will increment the display view by half increments.
>
>For example, consider a flight simulator which, say, updates 10 pixels in 1 frame in order to achieve a frame rate of 10fps.
>I would like to be able to then update 5 pixels in 1 frame to achive 20fps.
>
>Is this possible? And how would I go about programming it.
>
>Thanks for any info.
>

	What you do is determine the elapsed time from frame to frame each
time. On the amiga, the easiest and highest resolution way to do this is to
call ReadEClock, which returns a 64 bit count, and how many counts there
are per second. Subtract the previous value, and divide by (counts_per_sec>>15).
This will return an elapsed time in 32768th's of a second. Multiply all
incremental poistion increments by this fraction when determining how much
to move per frame.

	For instance, my simple movement code for moving at an arbitrary angle
along the ground is:

	move.w	PlayerHeading(a6),d0
	bsr	sincos	; d0=sin d1=cos
	move.w	frfract(a6),d2		; frfract=elapsed time 32768=1 sec
	muls	d2,d0
	muls	d2,d1
	add.l	d0,d0
	add.l	d1,d1
	swap	d0
	swap	d1
	move.w	PlayerSpeed(a6),d2
	muls	d2,d0
	muls	d2,d1
	add.l	d0,d0
	add.l	d1,d1
	swap	d0
	swap	d1
	ext.l	d0
	ext.l	d1
	add.l	d0,PlayerX(a6)
	add.l	d1,PlayerZ(a6)
	rts


	This will give the same movement rate on everything from an A500 to
an A4000.
-- 
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|Chris Green - Graphics Software Engineer   - chrisg@commodore.COM      f
|                  Commodore-Amiga          - uunet!cbmvax!chrisg       n
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