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uses crt;

type lrgarr = array[0..65534]of byte;

const
 pal : array[1..384]of byte =
 (0,0,0,48,48,48,1,0,43,1,3,43,2,5,44,2,7,44,3,9,45,4,11,46,5,13,47,6,15,48,
  7,17,49,8,19,50,9,21,51,10,22,52,11,24,52,12,26,54,13,28,54,14,30,56,15,32,
  56,16,34,58,17,34,58,17,36,58,18,38,60,19,40,60,20,42,62,21,44,62,10,31,0,
  11,31,0,11,31,1,11,32,1,12,32,1,12,32,2,12,33,2,13,33,2,14,33,3,15,33,3,15,
  34,3,15,34,4,15,35,4,16,35,4,16,35,5,16,36,5,17,36,5,17,36,6,18,37,6,18,38,
  7,19,38,8,20,39,8,20,40,9,21,40,10,22,41,10,22,42,11,23,42,12,24,43,12,24,
  44,13,25,44,14,25,45,14,26,46,15,27,46,16,27,47,17,28,47,18,28,48,19,29,49,
  19,30,49,20,30,50,21,31,51,21,32,51,22,32,52,23,33,53,23,34,53,24,34,54,25,
  35,55,25,36,55,26,36,56,27,37,57,27,38,57,27,39,57,27,41,57,27,42,57,27,43,
  57,27,44,57,27,45,57,27,46,57,27,47,57,27,49,57,27,50,57,27,51,57,27,52,57,
  27,53,57,27,55,57,27,56,57,27,57,57,27,58,57,27,58,57,26,58,57,25,58,57,24,
  58,56,23,58,55,22,58,54,20,58,53,19,58,51,18,58,50,17,58,50,16,58,49,15,58,
  48,14,58,47,13,58,46,12,58,45,11,58,44,11,58,44,10,58,43,10,58,42,9,57,41,
  8,57,40,8,56,39,7,56,38,6,55,37,5,55,35,4,54,33,4,54,31,2,32,32,32,63,63,63,
  63,63,63,63,63,63,63,63,63,48,48,48,63,63,63,63,63,63);

var
 mp,scr : ^lrgarr;
 rng : array[0..320]of byte;
 dir,i,x,y : integer;

function ncol(mc,n,dvd : integer): integer;
var loc : integer;
begin
 loc:=(mc+n-random(2*n)) div dvd; ncol:=loc;
 if loc>250 then ncol:=250; if loc<5 then ncol:=5
end;

procedure plasma(x1,y1,x2,y2 : word);
var xn,yn,dxy,p1,p2,p3,p4 : word;
begin
 if (x2-x1<2) and (y2-y1<2) then EXIT;
 p1:=mp^[256*y1+x1]; p2:=mp^[256*y2+x1]; p3:=mp^[256*y1+x2];
 p4:=mp^[256*y2+x2]; xn:=(x2+x1) shr 1; yn:=(y2+y1) shr 1;
 dxy:=5*(x2-x1+y2-y1) div 3;
 if mp^[256*y1+xn]=0 then mp^[256*y1+xn]:=ncol(p1+p3,dxy,2);
 if mp^[256*yn+x1]=0 then mp^[256*yn+x1]:=ncol(p1+p2,dxy,2);
 if mp^[256*yn+x2]=0 then mp^[256*yn+x2]:=ncol(p3+p4,dxy,2);
 if mp^[256*y2+xn]=0 then mp^[256*y2+xn]:=ncol(p2+p4,dxy,2);
 mp^[256*yn+xn]:=ncol(p1+p2+p3+p4,dxy,4);
 plasma(x1,y1,xn,yn); plasma(xn,y1,x2,yn);
 plasma(x1,yn,xn,y2); plasma(xn,yn,x2,y2);
end;

procedure draw(xp,yp,dir : integer);
var z,zobs,ix,iy,iy1,iyp,ixp,x,y,s,csf,snf,mpc,i,j : integer;
begin
 fillchar(rng,sizeof(rng),200);  zobs:=100+mp^[256*yp+xp];
 csf:=round(256*cos(dir/180*pi)); snf:=round(256*sin(dir/180*pi));
 fillchar(scr^,64000,0);
 for iy:=yp to yp+55 do
 begin
  iy1:=1+2*(iy-yp); s:=4+300 div iy1;
  for ix:=xp+yp-iy to xp-yp+iy do
  begin
   ixp:=xp+((ix-xp)*csf+(iy-yp)*snf) div 256;
   iyp:=yp+((iy-yp)*csf-(ix-xp)*snf) div 256;
   x:=160+360*(ix-xp) div iy1;
   if (x>=0) and (x+s<=318) then
   begin
    z:=mp^[256*iyp+ixp]; mpc:=z shr 1;
    if z<47 then z:=46;  y:=100+(zobs-z)*30 div iy1;
    if (y<=199) and (y>=0) then
     for j:=x to x+s do
     begin
      for i:=y to rng[j] do scr^[320*i+j]:=mpc;
      if y<rng[j] then rng[j]:=y
     end;
   end;
  end;
 end;
 move(scr^,mem[$A000:0],64000);
end;

begin
 writeln('Use arrow keys to pan in/out left/right ... any key to continue ..');
 readkey;
 randomize; x:=0; y:=0; dir:=0; new(mp); fillchar(mp^,65535,0);
 new(scr); mp^[$0000]:=128; plasma(0,0,256,256);
 asm xor ax,ax; mov al,$13; int $10; end;
 port[$3C8]:=0; for i:=1 to 384 do port[$3C9]:=pal[i];
 repeat
  dir:=dir mod 360; draw(x,y,dir);
  case readkey of
   #0 : case readkey of
     #75 : dec(dir,10);
     #77 : inc(dir,10);
     #72 : begin y:=y+round(4*cos(dir/180*pi));
           x:=x+round(4*sin(dir/180*pi)); end;
     #80 : begin y:=y-round(4*cos(dir/180*pi));
           x:=x-round(4*sin(dir/180*pi)); end;
       end;
   #27 : begin asm xor ax,ax; mov al,$3; int $10; end; HALT end
  end
 until false;
end.

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