Xref: utzoo comp.sys.amiga.tech:180 comp.sys.amiga:17217
Path: utzoo!mnetor!uunet!husc6!uwvax!puff!avery
From: avery@puff.cs.wisc.edu (Aaron Avery)
Newsgroups: comp.sys.amiga.tech,comp.sys.amiga
Subject: Re: How to smooth scroll left?
Message-ID: <1540@puff.cs.wisc.edu>
Date: 5 Apr 88 18:48:08 GMT
References: <4861@ecsvax.UUCP> <3313@csli.STANFORD.EDU>
Reply-To: avery@puff.WISC.EDU (Aaron Avery)
Organization: U of Wisconsin CS Dept
Lines: 28

In article <3313@csli.STANFORD.EDU> kasper@csli.UUCP (Kasper Osterbye) writes:
>	Scroll of screen rasterport 1 to the left
>		Using the build in rasterscroll.
Yes, ScrollRaster() is slow, since it has to move data in memory.

>- Apply amiga-guru trick #71.4 for smooth scrolling backgrounds, only I
OK, I'll tell you the best way I know of to do this and remain system-
compatible. What you want to do is set up (and allocate) a BitMap which is
the correct size for your entire background (if it's not too large). You then
open your screen with CUSTOMBITMAP set, putting the BitMap into the NewScreen
structure. Now, to actually do the scrolling, you find the screen's RasInfo
structure, which is in its ViewPort structure, which can be found in its
Screen structure. The value you want to manipulate is RasInfo->RxOffset. This
controls the X offset into the bitmap at which the left edge of the screen
begins. To update the display after changing the RxOffset, you might want
to use ScrollVPort(), as it's the most system-compatible method, but I've 
found that it has flashing problems when there are many (more than 2) bitplanes
present. You'll want to try it and see, tho. The other, faster, method is to
call MakeVPort(), then MrgCop(), and then LoadView(). Hope this helps.

Also, if your background is too large, you'll want to make a bitmap at least
twice the width of the display, and do some judicious copying into it to 
effect a circular buffer. If you want more on this, please mail me.


-- 
Aaron Avery (avery@puff.cs.wisc.edu)
	    ({seismo,caip,allegra,harvard,rutgers,ihnp4}!uwvax!puff!avery)