Path: news.uiowa.edu!chi-news.cic.net!news.uoregon.edu!cie-2.uoregon.edu!nparker
From: nparker@cie-2.uoregon.edu (Neil Parker)
Newsgroups: comp.sys.apple2
Subject: Re: Hires colors
Date: 31 Oct 1995 19:02:55 GMT
Organization: University of Oregon Campus Information Exchange
Lines: 62
Message-ID: <475rsv$ik3@pith.uoregon.edu>
References: <46r6tk$5us@news.cict.fr> <471rm5$j3i@acme.freenet.columbus.oh.us> <475g6l$79v@news.cict.fr>
NNTP-Posting-Host: cie-2.uoregon.edu

In article <475g6l$79v@news.cict.fr> frances@laas.fr (Fabrice Frances) writes:
>[...]
>however, I still find something unexplained : I've seen programs having blocs
>of blue pixels (Lode Runner for example 8-), how can it be done if two adjacent
>pixels become white ?

Blocks of solid color (other than black or white) are obtained by plotting
rows of alternating lit and unlit pixels.  For example, you can get a solid
blue horizontal line like this:

     byte 1     byte 2     byte 3     byte 4
     .BOBOBOB   .OBOBOBO   .BOBOBOB   .OBOBOBO
     XX.X.X.X   X.X.X.X.   XX.X.X.X   X.X.X.X.

(Where "B" indicates a "blue" column, "O" indicates an "orange" column, and
"X" indicates that the corresponding bit is set.  Note that the high bit of
each byte is set, so that we get blue and orange instead of purple and green.)

>Could you tell me the name of the command switching to hires, so that I try some
>pokes in the screen (I've tried HIRES, HRES, HRS with no success 8-(
>Also, I thought the hires mode was 160 pixels high, plus 4 text lines ?

The BASIC commands to enable hires are HGR and HGR2.  HGR displays (and clears
to black) hires page 1.  The graphics area is 280x160, with four lines of
text at the bottom.

HGR2 displays (and clears) hires page 2.  The graphics area is 280x192, with
no text at the bottom.

In both modes, the graphics commands accept Y coordinates in the range 0-191,
but when four lines of text are showing, the bottom 32 lines of graphics
are not visible.

The following POKE commands are also useful:

     POKE 49232,0   -- display graphics
     POKE 49233,0   -- display text

     POKE 49234,0   -- display full-screen graphics
     POKE 49235,0   -- display graphics with four lines of text

     POKE 49236,0   -- display page 1
     POKE 49237,0   -- display page 2

     POKE 49238,0   -- display lores graphics
     POKE 49239,0   -- display hires graphics

     POKE 230,32    -- select page 1 for drawing, even if page 2 is displayed
     POKE 230,64    -- select page 2 for drawing, even if page 1 is displayed

The sequence "HGR : POKE 49234,0" can be used to display hires page 1 without
the four lines of text.  Similarly, "HGR2 : POKE 49235,0" will display hires
page 2 with four lines of text, but this mode is less useful, since the four
lines of text come from text page 2 (which is normally occupied by your BASIC
program lines, and which the PRINT command won't use anyway).

               - Neil Parker
-- 
Neil Parker                       | No cute quote, no cute ASCII art, no cute
nparker@cie-2.uoregon.edu         | disclaimer, no deposit, no return....
nparker@cie.uoregon.edu           | (This space intentionally left blank:
http://cie-2.uoregon.edu/~nparker |                                           )