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Stolen Data 3.adf
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MAG-TEXT
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CODE5b
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1989-01-01
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31 lines
of the display buffer into the front
end of the update buffer, then plot the
new characters into the remaining
section. The scroll counter runs up to
256 pixels (32 bytes) which means
copying the remaining 48 bytes. I copy
4 bytes per line every frame, so for a
16*16 scroller in one bitplane this
involves a copy of just 32 words (64
bytes) with the blitter, and it takes
12 frames to copy the lot. Then we get
to plotting the new characters, again
assuming a 16*16 font, I plot 2
characters a frame and we need 32/2=16
of these so it takes 8 frames to finish
the plotting procedure.
In order to plot the new characters
we have a pointer to the scrolltext
which is incremented each frame, and
set back to the start when a zero byte
is detected. Fonts can be stored in a
number of ways. Some people advocate
the method of storing each character
below the previous. To calculate the
position of a particular letter or
symbol you multiply the character code
by a constant factor, the size of every
character. The main difficulty here is
putting the font into the correct
format in the first place but there