my attempt at Ray Marching Distance Fields

                                    ` This code was downloaded from The Game Creators
                                    ` It is reproduced here with full permission
                                    ` http://www.thegamecreators.com
                                    
                                    Rem Project: Ray Marching Version 1
Rem Created: Sunday, September 25, 2011

Rem ***** Main Source File *****

//
Type rtVec
 x as float
 y as float
 z as float
EndType

//
Randomize Timer()

//
Dim RayDir(256*256) as rtVec
Dim RayCol(256*256) as rtVec

//
For i = 0 To 255
 For j = 0 To 255
  dx# = i - 128.0
  dy# = j - 128.0
  dz# = 128.0
  dm# = 1.0 / Sqrt( dx# * dx# + dy# * dy# + dz# * dz# )
  RayDir(i+j*256).x = dx# * dm#
  RayDir(i+j*256).y = dy# * dm#
  RayDir(i+j*256).z = dz# * dm#
  RayCol(i+j*256).x = i * dm#
  RayCol(i+j*256).y = j * dm#
  RayCol(i+j*256).z = dz# * dm#
 Next
Next

//
ox# = 0
oy# = 0
oz# = -1280

Repeat

 aa# = WrapValue(aa#+1.0)
 cc# = Cos(aa#)
 ss# = Sin(aa#)
   
 inc oz# , 1
 
 ox#=ox#+cc#
 oy#=oy#+ss#

 //
 lx# = ox#-100
 ly# = oy#-1000
 lz# = oz#-1000.0
   
 Cls 0x0
 
 Lock Pixels
 
 For i = 0 To 255 Step 2

  For j = 0 To 255 Step 2
   
   dii = i + ( j << 8 )
    
   dx# = RayDir(dii).x
   dy# = RayDir(dii).y
   dz# = RayDir(dii).z

   ty# = dy# 
   dy# = dy# * cc# - dz# * ss#
   dz# = dz# * cc# + ty# * ss#

   tx# = dx#
   dx# = dx# * cc# - dz# * ss#
   dz# = dz# * cc# + tx# * ss#

   tx# = dx#
   dx# = dx# * cc# - dy# * ss#
   dy# = dy# * cc# + tx# * ss#

   rx# = ox#
   ry# = oy#
   rz# = oz#
          
   For k = 0 To 256
    
    fx# = ( rx# + 256 ) Mod 64
    fy# = ( ry# + 256 ) Mod 64
    fz# = ( rz# + 256 ) Mod 64
        
    di# = Sample( fx# , fy# , fz# )
   
    //
    If di# > 1000.0
     Flag = 0
     Exit
    Endif

    //
    If di# < 0.0001
     
     Flag = 1
 
     Exit
 
    Endif
   
    rx# = rx# + di# * dx#
    ry# = ry# + di# * dy#
    rz# = rz# + di# * dz#
      
   Next
 
   If Flag = 1

    ep# = 0.000009
    
    nx# = (rx# - ep#) - ( rx# + ep# )
    ny# = (ry# - ep#) - ( ry# + ep# )
    nz# = (rz# - ep#) - ( rz# + ep# )
    
    nm# = 1.0 / Sqrt( nx# * nx# + ny# * ny# + nz# * nz# )
    
    nx# = nx# * nm#
    ny# = ny# * nm#
    nz# = nz# * nm#
     
    ix# = lx# - rx#
    iy# = ly# - ry#
    iz# = lz# - rz#
    
    im# = 1.0 / Sqrt( ix# * ix# + iy# * iy# + iz# * iz# )
    
    ix# = ix# * im#
    iy# = iy# * im#
    iz# = iz# * im#

    lc# = ix# * nx# + iy# * ny# + iz# * nz#
   
    If lc# > 0
 
     df# = lc# * 0.9 
    
     rc# = ( RayCol(dii).x ) * df#
     gc# = ( RayCol(dii).y ) * df#
     bc# = ( RayCol(dii).z ) * df#
 
     //
     Dotx2(i,j,Rgb(rc#*255,gc#*255,bc#*255),2)
             
    Endif
   
    Flag = 0
   
   Endif
      
  Next
 
 Next

 Unlock Pixels

Until EscapeKey()

End

Function Dotx2(x,y,c,s)
 If s > 0
  DotFast(x,y,c)
  s = s >> 1
  Dotx2(x  ,y  ,c,s)
  Dotx2(x  ,y+1,c,s)
  Dotx2(x+1,y+1,c,s)
  Dotx2(x+1,y  ,c,s)
 Endif
EndFunction

//
Function DotFast(x,y,c)
 Pixel = Get Pixels Pointer() + ( y * Get Pixels Pitch() + ( x << 2 ) )
 *Pixel = c
EndFunction

//
Function Min(a#,b#)
 if a# > b# then exitfunction b#
EndFunction a#

//
Function Max(a#,b#)
 if a# < b# then exitfunction b#
EndFunction a#

//
Function rmCube(x#,y#,z#,s#)
 a# = Max( Abs(x#) - s# , 0.0 )
 b# = Max( Abs(y#) - s# , 0.0 )
 c# = Max( Abs(z#) - s# , 0.0 )
 d# = Max(a#,Max(b#,c#)) 
EndFunction d#

//
Function rmSphere(x#,y#,z#,r#)
 d# = Sqrt( x# * x# + y# * y# + z# * z# ) - r#
EndFunction d#

//
Function Sample(x#,y#,z#)
 di# = rmCube(x#,y#,z#,20.0)
EndFunction di#