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From: nparker@cie-2.uoregon.edu (Neil Parker)
Newsgroups: comp.sys.apple2.programmer
Subject: Re: SHR Screen loading
Date: 27 Oct 1994 06:09:58 GMT
Organization: University of Oregon Campus Information Exchange
Lines: 48
Message-ID: <38ng7m$k7q@pith.uoregon.edu>
References: <1994Oct26.011242.13526@news.stolaf.edu>
NNTP-Posting-Host: cie-2.uoregon.edu

In article <1994Oct26.011242.13526@news.stolaf.edu> handel@lars.acc.stolaf.edu
(Peter F Handel) writes:
>What's the easiest way to display a Super High Res screen?
>It'd be a uncompressed SHR screen; I'd have to load it into
>$E1/2000 & then turn it on with C029:C1 (or 41), right?  Well, 
>BLOAD PIC,A$E1/2000 doesn't work (from BASIC) and I'd like 
>to actually write it as a $FF system file in Merlin.  ProDOS 8
>will have been loaded.

1.  BLOAD PIC,A$1000,T$C1.
2.  Turn on the SHR linearization bit.  You can also turn on the SHR display
    switch at the same time if you want.  (LDA #$40; TSB $C029)
3.  Call a machine language routine to copy $8000 bytes from $00/1000 to
    $E1/2000.

          PHB
          CLC
          XCE
          REP #$30
          LDX #$1000
          LDY #$2000
          LDA #$8000
          MVN $00E1
          SEC
          XCE
          PLB
          RTS

4.  If you didn't turn on the SHR display switch in step 2, do it now.
    (LDA #$C0; TSB $C029)

Note that regardless of when you make the SHR screen visible, you must
always turn on the linearization bit BEFORE writing to the screen.  Failure
to do so will make your pictures come out scrambled.

>I guess I could blank the SHR screen, draw lines on it with loops,
>and then turn the screen on, but that would take forever.  The pic
>I want displayed isn't too complex; is loading a compressed pic a
>lot harder than loading a 65-block uncompressed pic?

Loading a compressed picture is a little bit harder, because you have to
uncompress it first.

               - Neil Parker
--
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