Subject: Re: Bug in ViewPorts under 2.0
From: [email-masked] (Chris Green)
Date: 17 Nov 92 12:31:59 GMT
Newsgroups: comp.sys.amiga.programmer

In article <[email-masked]> [email-masked] (Adisak Pochanayon) writes:
>
>    I have been writing some code that performs horizontal scrolling of
>extremely large bitmaps (quickly).  This code works properly under both
>1.3 and 2.0 in lowresolution.  It also works under 1.3 in hi-res fine.
>However, when I use 2.0 and hi-res I get a wierd problem.  The RxOffset
>in the RasInfos structure shifts the offset into the bitmap by two
>pixels instead of 1.  Is this a bug under 2.0???  Or do I have to set
>any special flags in the view or viewport that I'm using.  Has anybody
>tried horizontal scrolling with a hires screen???  Why can 1.3 be accurate
>in scrolling to a single pixel and then 2.0 only to multiples of two
>(actually, it multiplies RxOffset by two or at least that's the way I
>can duplicate the result in 1.3).
>
>    Please e-mail me with any help at [email-masked] asap.
>Thanks.

	This is the infamous "RxOffset Bug". 1.1,1.2,1.3, + 3.0 interpret the
RxOffset in the correct manner (as hires pixels). Somehow 2.0 started
interpreting it as low-resolution coordinates without anyone noticing
before it was too late. This was fixed in 3.0. You'll have to make
your code version sensitive.

-- 
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|Chris Green - Graphics Software Engineer   - [email-masked]      f
|                  Commodore-Amiga          - uunet!cbmvax!chrisg       n
|My opinions are my own, and do not         - icantforgettheimpression  o
|necessarily represent those of my employer.- youmadeyouleftaholeinthe  r
|"A screaming comes across the sky..."      - backofmyhead              d
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