Atari 800 Basic Reference Manual

COLOR (C.)
DRA WTO (DR.)
LOCATE (LOC.)
Format: COLOR aexp
Examples: 110 COLOR ASC("A")
110 COLOR 3
The value of the expression in the COLOR statement determines the data to be
stored in the display memory for all subsequent PLOT and DRA WTO com-
mands until the next COLOR statement is executed . The value must be positive
and is usually an integer from 0 through 255. Non-integers are rounded to the
nearest integer. The graphics display hardware interprets this data in different
ways in the different graphics modes . In text modes 0 through 2, the number
can be from 0 through 255 (8 bits) and determines the character to be displayed
and its color. (The two most significant bits determine the color . This is why on-
ly 64 different characters are available in these modes instead of the full
256-character set.)
Tables 9-6 and 9-7 at the end ofthis section illustrate the internal character set
and the character / color assignment. Table 9-2 is a simplified table which a llow s
easy
generation of some of the colors. For example, COLOR ASC(" A"): PLOT
5,5 will display an orange A character in graphics modes 1 or 2 at location 5,5.
Graphics modes 3 through 8 are not text modes, so the data stored in the display
RAM simply determines the color of each pixel. Two-color or two-luminance
modes require either 0 or 1 (1-bit) and four-color modes require 0, 1, 2, or 3. (The
expression in the COLOR statement ma y have a value greater than 3, but onl y
one or two bits will be used.) The actual color which is displayed depends on the
value in the color register which corre s ponds to the data of 0, 1, 2, or 3 in the
pa rti c ular graphi cs mode be ing us ed . This · ma y be dete rmin ed by looking in
Table 9-5, which gives the default colors and the corresponding register
numbers. Colors may be changed by using SETCOLOR.
Note that when BASIC is first powered up, the color data is 0, and w hen a
GRAPHICS command (without + 32) is executed , all of the pixels are set to 0.
Therefore, nothing seems to happen to PLOT and DRA WTO in GRAPHICS 3
through 7 when no COLOR stateme nt has b ee n ex ec ut ed. Cor rec t by doing a
COLOR 1 first .
Fonnat:
Example:
DRA WTO aexp1, ae xp2
100 DRA WTO 10, 8
This st ate ment ca us es a lin e to be d raw n fr om th e la st po int di s pl ay ed by a PLOT
(see
PLOT) to the location specified by aexp1 and aexp2. The first expression
represents the X coordinate and the s econd represent s the ¥-coordinate (see
Fig
ur e 9-1). The color of th e lin e is th e sam e co lor as th e po in t di s pla ye d by th e
PLOT.
Format:
Example:
LOCATE a exp1, ae xp2 , va r
150 LOCATE 1
2, 15, X
This command positi o ns the in visible graphics cursor at the specified lo c ation in
th e g ra ph ics w ind ow, retri eve s th e data at th at pi xe l, a nd stor es it in th e
specified arithmetic v ariable . T his gi ves a number from 0 to 255 for Graphics
mode s 0 through 2; 0 or 1 for the 2-color graphic s modes ; and 0, 1, 2, or 3 for the
4-co lor modes. Th e tw o ar ithm e ti c ex p re ssions spe ci fy the X a nd Y coo rdin at es
of th e point . LO CA TE is e qui va le nt to:
POSITION
aexp1 , a exp 2:GET # 6, av ar
48 Graphic Modes a nd Co mmwu is

Atari 800 Specifications

General

Brand	Atari
Model	800
Category	Desktop
Language	English