Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!ptsfa!well!ewhac
From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.sys.amiga
Subject: Re: I've Got Sprite Troubles
Keywords: Why me?
Message-ID: <5223@well.UUCP>
Date: 12 Feb 88 20:03:18 GMT
References: <1669@ssc-vax.UUCP>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: The CIA:  Third-World Governments Destabilized While-U-Wait.
Lines: 48

In article <1669@ssc-vax.UUCP> dmg@ssc-vax.UUCP (David Geary) writes:
>However, when I move the sprite (ball) around on the 
>screen, the previous image of the sprite does not
>completely disappear before the sprite is redrawn
>at the new position.  As a matter of fact, at
>a higher speed, I can distinctly see 3 images
>at once.
>
>Can anyone help me?  I'm on an A1000, using
>Lattice 3.03.  [ ... ]
>^^^^^^^^^^^^^
>help,
>     help,
>          help...
>
	There's your problem right there :-).

	Seriously, I don't know what the problem is; I can only guess.  Have
some guesses:

	There are two possibilities that I can think of.  One is that you're
not moving the pointer fast enough.  You have to move it at least 15 frames
per second to eliminate most of the jittering effects.  Have you tried
writing a short standalone program that does nothing but move the pointer in
a tight loop, and see how that works?

	The other possibility is that you're moving the pointer *too* fast.
That is to say, your program is running so fast that your sprite location
data and hardware registers are being updated faster than the field rate.

	The hardware displays the sprite.  Meanwhile, you've updated the
position, and called MoveSprite() (which is really ChangeSprite() in
disguise).  The routine stomps the hardware sprite data register, and the
hardware starts DMA'ing from that point.  It sees the new position, waits
for the video beam to go there, and starts displaying it again.

	This seems highly implausible to me.  Nevertheless, are you using
WaitTOF() between each of your calls to MoveSprite()?

	Note that I'm just guessing.  I have a hard time believing the
problem exists at all, since I've never seen it before.  If these
suggestions don't work, I'd be willing to take a look at the executable.

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Leo L. Schwab -- The Guy in The Cape	ihnp4!ptsfa -\
 \_ -_		Recumbent Bikes:	      dual ---> !{well,unicom}!ewhac
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