mode 1,8
cls
dim float height(100,100)
dim integer xarray (3)
dim integer yarray (3)

page write 0
DrawMountains(1)
DrawMountains(2)
DrawMountains(3)

sub DrawMountains(formula)
 ' Calculate the grid of values
 for x=-50 to 50
   for y=-50 to 50
     distance = sqr(x*x+y*y)
     distance2 = sqr ((X-10) * (x-10) + (y-10) * (y-10))
     distance3 = sqr(abs ((x+22) * (x+12) + (y+11) * (y+3)))
     if formula=1 then height(x+50, y+50) =cos(distance2/3) * sin(distance/4)* sin(distance3) * (50-distance)* 2.4
     if formula=2 then height(x+50, y+50) = sin(distance2/10) * cos(distance/4) * cos(distance3/2) * (30-distance)*1.6
     if formula=3 then height(x+50, y+50) = sin(x/10) * cos(distance/4) * cos(distance3/2) * (30-distance)*0.8
     if height(x+50,y+50)<1 then height (x+50, y+50)=1

     'Make the last height equal to the first so that it is seamless
     if x=50 then height(x+50,y+50) = height(0,y+50)
   next y
 next x

 ' Plot each rectangle as a filled polygon
 for x=1 to 100
   for y=1 to 100
     ' Is this the second (wrapped) line?
     tempx = GetOnScreenX(x,y)
     yoffset=(formula-1)*200
     xoffset=0
     if (tempx>799) then
       xoffset=-800
       yoffset=(formula-1)*200 + 100
     end if    

     xarray(0)=GetOnScreenX(x-1,y-1) + xoffset
     yarray(0)=GetOnScreenY(x-1, y-1) + yoffset
     xarray(1)=GetOnScreenX(x,y-1) + xoffset
     yarray(1)=GetOnScreenY(x,y-1) + yoffset
     xarray(2)=GetOnscreenX(x,y) + xoffset
     yarray(2)=GetOnScreenY(x,y) + yoffset
     xarray(3)=GetOnScreenX(x-1,y) + xoffset
     yarray(3)=GetOnScreenY(x-1,y) + yoffset
   
     r = abs(height(x,y))*6
     if r>255 then r=255
     if (formula=1) then polygon 4, xarray(), yarray(), RGB(0,80,0), RGB(0,0,0)
     if (formula=2) then polygon 4, xarray(), yarray(), RGB(0,128,0), RGB(0,40,0)
     if (formula=3) then polygon 4, xarray(), yarray(), RGB(0,255,0), RGB(0,80,0)
   next y
 next x
end sub

function GetOnscreenX (x,y)
 GetOnScreenX = y*2 + (x*16)
 rem if GetOnscreenx > 800 then GetOnscreenX = GetOnScreenX-800
end function

function GetOnScreenY (x,y)
 rem GetOnScreenY = 500 - (y*2) - height(x,y)
 GetOnScreenY = 100 - height(x,y)
 rem if GetOnScreenX(x,y) > 800 then GetOncreenY = GetOnScreenY + 200
end function

mode 1,8
cls
for animation=1 to 20
 yoffset= 200+(animation-1)*10
 line 0,yoffset,800,yoffset,1,rgb(0,255,0)
 line 0,yoffset+4, 800, yoffset+4,1,rgb(0,255,0)
 line 0,yoffset+9, 800, yoffset+9,1,rgb(0,255,0)

 for verticals = 1 to 10
   xoffset = animation*4
   x1 = xoffset+ (80*verticals)
   x2 = 400 + ((x1-400)*1.2)
   line x1,yoffset, x2, yoffset+9,1,rgb(0,255,0)
 next verticals
next animation