'Sphere for FreeBASIC May 2015
'spherefb4.bas
'Sphere using XPL0 code from rosetacode sphere page
'
screenres 640,480,32   '\set 640x480x32 graphics mode
windowtitle "32 bpp Blue Sphere FreeBASIC"
'
' wait until keypress
locate 50,2
color(rgb(255,255,255),rgb(0,0,0))
Print "Enter any key to start"
sleep
 R=100 : R2=R*R	               '\radius, in pixels; radius squared
 X0=640/2 : Y0=480/2           '\coordinates of center of screen
 dim as integer X, Y, Z, C, D2 '\coords, color, distance from center squared
'
for Y= -R to +R                '\for all the coordinates near the circle
    for X = -R to +R          '\ which is under the sphere
        D2 = X*X + Y*Y        '
        C = 0                  '\default color is black
        if D2 <= R2 then       '\coordinate is inside circle under sphere
            Z = sqr(R2-D2)     '\height of point on surface of sphere above X,Y
            C = Z-(X+Y)/2+130  ' \color is proportional; offset X and Y, and
        endif
         color c                ' \ shift color to upper limit of its range
                                '\green + blue = cyan orginal line don't understand
         Pset(X+X0, Y+Y0)
    next x
  next y
'
' wait until keypress
locate 50,2
color(rgb(255,255,255),rgb(0,0,0))
Print "Enter any key to exit "
sleep
END