{> Cut here. FileName= SPHERE.PAS }
program sphiere;
uses graph,crt;
type vect=array[1..3] of real;
const
  Il=1;
  Ia=0.6;
  ka=0.15;
  kd=0.2;
  ks=0.8;
  st:byte=3;
  rr:real=0;
  aa=1;
  l:vect=(-1,0,1);
  s:vect=(0,0,1);
  _s=50;
  _r=30;

var
  driver,mode : integer;
  i,j,cyc     : integer;
  r,n         : vect;
  ys,xs       : integer;
  p           : pointer;
  size        : word;
  ex          : boolean;
  key         : char;
  min         : real;
  cfi,ca      : real;

Procedure SetRGB(c,r,g,b:byte);
begin
 port[$3c8]:=c;
 port[$3c9]:=r;
 port[$3c9]:=g;
 port[$3c9]:=b
end;

Function w(c:real):real;
begin
 w:=(c-0.5)*(c-0.5)/2+0.7
end;

Function Step(c:real;a:byte):real;
var
  i:byte;
  r:real;
begin
 r:=1;
 for i:=1 to a do r:=r*c;
 step:=r
end;

Procedure sph(x,y,rad:integer;b:boolean);
var
 i,j,q,c:integer;
 len_l,len_r,len_s:real;
begin
 len_l:=sqrt(sqr(l[1])+sqr(l[2])+sqr(l[3]));
 if not b then rr:=0.8/abs(l[1]/len_l*x/640+l[2]/len_l*y/480+l[3]/len_l);

 if rr>min then min:=rr;
 for j:=-rad to rad do
  begin
   q:=trunc(sqrt(rad*rad-j*j));
   for i:=-q to q do
    begin
     n[1]:=i/rad;
     n[2]:=j/rad;
     n[3]:=sqrt(rad*rad-i*i-j*j)/rad;

     cfi:=(n[1]*l[1]+n[2]*l[2]+l[3]*n[3])/len_l;
     if cfi<0 then cfi:=0;
     for cyc:=1 to 3 do r[cyc]:=2*cfi*len_l*n[cyc]-l[cyc];{2*cfi}
     len_r:=sqrt(r[1]*r[1]+r[2]*r[2]+r[3]*r[3]);
     len_s:=sqrt(s[1]*s[1]+s[2]*s[2]+s[3]*s[3]);
     ca:=(r[1]*s[1]+r[2]*s[2]+r[3]*s[3])/(len_r*len_s);
     if (ca=1)and(l[3]=-r[3]) then ca:=0;
     if ca<0 then ca:=0;

     c:=trunc(63* (Il/(rr+aa)*(kd*cfi+ks*step(ca,st)) + Ia*ka));

     putpixel(x+i,y+j,c);
    end;
  end;
end;

begin
 driver:=InstallUserDriver('svga256', nil);
 mode:=2;
 InitGraph(driver, mode, '');
 randomize;
 ClearDevice;
 for i:=1 to 63 do setRGB(i,i,i,i);
 setcolor(5);
 line(0,0,300,0);
 xs:=100;ys:=100;
 ex:=false;
 size:=ImageSize(0,0,100,100);
 GetMem( p, size);
 repeat
  GetImage( xs-_r, ys-_r, xs+_r, ys+_r, p^);
  sph(xs,ys,_r,false);
  key:=readkey;
  if key=#0 then key:=readkey else
   begin
    ex:=(key=#27);
    if key=#13 then
     begin
      for j:=-3 to 3 do begin
       l[1]:=sqrt(9-j*j);
       l[2]:=j;
       sph(xs,ys,_r,true)
      end;
      for j:=2 downto -2 do begin
       l[1]:=-sqrt(9-j*j);
       l[2]:=j;
       sph(xs,ys,_r,true)
      end;
     end;
   end;
  PutImage( xs-_r, ys-_r, p^, NormalPut);
  case ord(key) of
   75 : if xs>60 then dec(xs,_s);
   77 : if xs<520 then inc(xs,_s);
   80 : if ys<420 then inc(ys,_s);
   72 : if ys>60 then dec(ys,_s)
   end;
 until ex;

 closegraph
end.