Re: Fill Maze

[tgeer@pro-gumbo.cts.com (System Administrator)]

In <19630@mindlink.bc.ca>
Clayten_Hamacher@mindlink.bc.ca (Clayten Hamacher) writes:

>I used to have docs for Fill Maze which described the method of drawing an
>entire line with one 'command'. Does someone have these docs or a text on
>doing this in general? P.S. What apple manual would this be in?

If a scan line enables fill mode by having bit 5 of its SCB (scanline control
byte) set to 1, that line has only 15 active colors.  The 0th color in the
table is inactive.  Instead, a pixel with a 0 color value is a signal to the
super hires circuitry to display that pixel in the same color as the previous
pixel on that line.  Thus, a scan line with fill mode enabled, and with the
values:
        3 0 0 0 0 0 0 0 7 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

is the equivalent of:

        3 3 3 3 3 3 3 3 7 7 7 7 7 7 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

Fill mode is most useful, obviously, in drawing filled shapes.  In the above
example, assuming your scan line data was previously all zeros, this entire
line could have been displayed by writing only 3 bytes instead of 30 bytes -
a considerable savings in CPU time.  NOTE: fill mode is NOT compatible with
the 640 mode display.  Additionally, if fill mode is to be used then the
first color of a scan line MUST NOT be 0 or unpredictable results may occur.

This data was derived from 'Apple IIGS Technical Reference' from Osborne,
McGraw-Hill, written by Michael Fischer.  It may also be found in the
'Apple IIGS Hardware Reference' from Apple Computer and various other
publications.


----------------------------------------------------------------------------
ProLine: tgeer@pro-gumbo          Internet: tgeer@pro-gumbo.cts.com
UUCP:    crash!pro-gumbo!tgeer    Fidonet:  tom.geer@f20.n380.z1.fidonet.org
----------------------------------------------------------------------------
"My wife is a bargain hunter - I just carry the ammunition."