'Mandelbrot V4 for RunBasic
'Based on LibertyBasic solution
'copy the code and go to runbasic.com
'http://rosettacode.org/wiki/Mandelbrot_set#Liberty_BASIC
'May 2015 (updated 29 Apr 2018)
'
'Note - we only get so much processing time on the server, so the
'graph is computed in three or four pieces
'
WindowWidth  = 320  'RunBasic max size 800 x 600
WindowHeight = 320
'print zone -2 to 1 (X)
'print zone -1.5 to 1.5 (Y)
a = -1.5  'graph -1.5 to -0.75, first "loop"
b = -0.75  'adjust for max processor time (y0 for loop below)

'open "Mandelbrot Set" for graphics_nsb_nf as #w  not used in RunBasic

graphic #w, WindowWidth, WindowHeight
'#w "trapclose [quit]"       not used in RunBasic
'#w "down"                   not used in RunBasic

cls
'#w flush()
#w cls("black")
render #w
 '#w flush()
input "OK, hit enter to continue"; guess
cls

[man_calc]
'3/screen size 3/800 = 0.00375  ** 3/790 = 0.0037974
'3/screen size (y) 3/600 = .005 ** 3/590 = 0.0050847
'3/215 = .0139 .0068 = 3/440
cc = 3/299
'
    for x0 = -2 to 1 step cc
    for y0 = a to b step  cc
        x = 0
        y = 0

        iteration    =   0
        maxIteration = 255

        while ( ( x *x +y *y) <=4) and ( iteration <maxIteration)
            xtemp      =x *x -y *y +x0
            y          =2 *x *y +y0
            x          = xtemp
            iteration  = iteration + 1
        wend

        if iteration <>maxIteration then
            c =iteration
        else
            c =0
        end if

        call pSet x0, y0, c
        'scan why scan? (wait for user input) with RunBasic ?
    next
next

'#w flush()  'what is flush? RunBasic uses the render command.
render #w

input "OK, hit enter to continue"; guess
cls
a = a + 0.75
b = b + 0.75
if b > 1.6 then goto[quit] else goto[man_calc]

sub pSet x, y, c
    xScreen = 5+(x +2)   /3 * 300 'need positive screen number
    yScreen = 5+(y +1.5) /3 * 300 'and 5x5 boarder
    if c =0 then
        col$ ="red"
    else
        if c mod 2 =1 then col$ ="lightgray" else col$ ="white"
    end if
    #w "color "; col$
    #w "set "; xScreen; " "; yScreen
end sub

[quit]
'cls
print
print "This is a Mandelbrot Graph output from www.runbasic.com"
render #w
print "All done, good bye."
end