RosettaCodeData/Task/Greyscale-bars-Display/BBC-BASIC/greyscale-bars-display.basic

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MODE 8:REM 640 x 512 pixel display mode: BBC BASIC gives 2 graphics points per pixel
REM (0,0) is the bottom left of the display
GCOL 1 :REM Select colour one for drawing
FOR row%=1 TO 4
n%=2^(row%+2)
w%=1280/n%
py%=256*(4-row%)
FOR b%=0 TO n%-1
g%=255*b%/(n%-1)
IF n%=16 OR n%=64 THEN g%=255-g%
COLOUR 1,g%,g%,g% : REM Reprogram colour 1 to the grey we want
RECTANGLE FILL w%*b%,py%,w%,256
NEXT b%
NEXT row%