'   Draws two sets of concentric circles.
'   Spacing, colour and linewidth different each time.
'   Result shows how superposed wavefronts 'interfere'.
'   But basically eye candy- a programming exercise,

nomainwin

WindowWidth  = 900
WindowHeight = 700
UpperLeftX   =  50
UpperLeftY   =  50

graphicbox #john.g1,      10,  10, 880, 680

button     #john.b1, "Draw", [drawThem], UL, 400, 20
button     #john.b2, "Quit", [quit],     UL, 400, 60

open "R-theta coordinates-- Interference patterns & Moire patterns" for window as #john

#john, "trapclose [quit]"
wait


[drawThem]
wby2 =int( 90 *rnd(1))+10   ' move centres left and right to sep'n of w
sze  =int( 6 *rnd(1))+1     ' this will be the width of line

#john.g1, "goto "; 450 -wby2; " 340 ; down ; fill white ; size "; sze
#john.g1, "color "; int( 256*rnd(1)); " "; int( 256*rnd(1)); " ";int( 256*rnd(1))

for circle =1 to 60
    #john.g1, "circle "; circle *10
    scan
next circle

#john.g1, "up ; goto "; 450 +wby2; " 340 ; down"

for circle =1 to 60
    #john.g1, "circle "; circle *10
    scan
next circle

wait

[quit]
    close #john
    end