Radio Shack TRS-80 Model 100 Basic Manual page 106

You can draw lines very easily on your Model 100. For example, to draw a line from
the upper left corner to the lower right corner of the display, enter:
CLS (ENTER)
LINE (O,O) - (239,63)
CEBllID
Similarly,
LINE (O,63) - (239,O) (ENTER)
will draw a line from the lower left to the upper right corner. As with the PSET
instruction, the first number in the parentheses is the horizontal (X) axis position and
the second number is the vertical (Y) axis position. The first set of coordinates is the
starting cell and the second set of coordinates is the ending cell.
To erase a line, simply add a zero after the second coordinate:
L1NE(0,63) - (239,O),O (ENTER)
A simple extension of the LINE instruction makes it easy to draw a box:
CLS
CEtffiID
LINE (30,8) - (210,56),1,B (ENTER)
Graphic data, such as lines and boxes, can appear on the LCD display at the same
time as text. The number I after the second set of coordinates says to draw the line
with dark cells. The letter B at the end of the instruction says to draw a box whose
opposite corners are defined by the two coordinates.
To erase a box, simply change the 1 to a 0:
LINE (30,8) - (210,56),0,B (ENTER)
It is just as easy to draw a filled in box:
CLS~
LINE (210,27) - (230,37),1 ,BF
CEfIllID
To erase a rectangular area on the display, change the 1 to a 0:
LINE (213,30) - (227,34),0,BF (ENTER)
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