Commodore Plus 4 - Page 205

Graphics Programming in BASIC 193
the left of the screen to 319 at the right. The vertical (or y) coordinate ranges from
0 at the top of the screen to 199 at the bottom. Only the CHAR statement (which
plots characters on the high-resolution screen) uses the text rows and columns for
its coordinates. The CHAR x and y are related to the high-resolution x and y by
CHAR coordinate = INT(high-resolution coordinate/'8)
Colors in High Resolution The background and border colors of the screen can
be changed as usual with the commands:
COLOR 0, color, luminance
and
COLOR 4,color,luminance
The other color available in high resolution is foreground. The foreground color
is set with
COLOR 1,color,luminance
In each of the drawing statements, you can specify the use of foreground or
background color.
Although you can choose to set (to foreground color) or clear (to background
color) each pixel on the screen in this mode, the colors of some pixels are not
independent. The background color is globally defined. Whenever you change
COLOR 0, every background colored pixel changes color. Also, each 8-pixel-by-
8-pixel character cell on the screen is assigned a single foreground color. This
means that every pixel set to foreground color within a character cell is the same
color. If you change foreground colors between two drawings to the same
character cell, the color of pixels drawn both times will be the color used last.
However, each of the 1000 character cells has an independent color (and lumi
nance), allowing for a great deal of creative color usage, even in high-resolution
mode.
Whenever you draw a pixel, whether in foreground or background color, the
foreground color for its character cell is set to the current foreground color. This
is normally the desired effect when you are drawing in foreground color. But
when drawing in background color, one would expect the foreground colors to be
unaffected. Unfortunately, this is not the case. If you have drawn in foreground
color in a character cell, and you return to draw in background color, the
foreground color of that cell is updated to your current foreground color. If you