PROGRAM site
! draw site percolation configurations           
DIM rsite(64,64)
LIBRARY "csgraphics"
! define lattice and screen parameters
CALL initial(rsite(,),L,p,delta_p,occup$)
! occupy sites for given probability p
CALL configuration(rsite(,),L,p,delta_p,occup$)
END

SUB initial(rsite(,),L,p,delta_p,occup$)
    RANDOMIZE
    INPUT prompt "linear dimension of square lattice = ": L
    INPUT prompt "initial probability p = ": p
    ! desired increase in p upon mouse click
    INPUT prompt "delta p = ": delta_p
    CALL compute_aspect_ratio(L,xwin,ywin)
    SET WINDOW -0.1*xwin,xwin,-0.1*ywin,ywin
    ! represent occupied site as blue circle with unit diameter
    SET COLOR "blue"
    BOX CIRCLE 2,3,2,3
    FLOOD 2.5,2.5
    BOX KEEP 2,3,2,3 in occup$
    CLEAR
    SET COLOR "black"
    LET r = 0.5
    BOX LINES 1-r,L+r,1-r,L+r
    FOR y = 1 to L                ! draw lattice sites 
        FOR x = 1 to L
            ! assign random number to each lattice site
            LET rsite(x,y) = rnd
            PLOT POINTS: x,y
        NEXT x
    NEXT y
END SUB

SUB configuration(rsite(,),L,p,delta_p,occup$)
    DO while p <= 1
       SET CURSOR 1,1
       PRINT "p =";p
       FOR y = 1 to L
           LET yplot = y - 0.5
           FOR x = 1 to L
               IF rsite(x,y) < p then
                  LET xplot = x - 0.5
                  BOX SHOW occup$ at xplot,yplot
               END IF
           NEXT x
       NEXT y
       BOX LINES 0.5,L+0.5,0.5,L+0.5   ! redraw lines
       DO
          DO
             GET MOUSE xs,ys,state
          LOOP until state = 2
          ! click on occupied site to see cluster
          ! click mouse to right of lattice to increase p by delta_p
          IF (xs < L and xs > 0) and ys <= L then
             SET COLOR "red"
             FLOOD xs,ys
          END IF
       LOOP until xs > L
       LET p = p + delta_p
       SET COLOR "black"
    LOOP
END SUB