uses crt,graph;
type
PixelType=record
x,y:integer;
end;
const
N=5000;
var
d,r,e,k:integer;
x1,y1,x2,y2:integer;
a:array[1..N] of  PixelType;
begin
d:=Detect;
InitGraph(d,r,'');
e:=GraphResult;
if e<>grok then
writeln(GraphErrorMsg(e))
else
begin
x1:=getmaxX div 4;
y1:=getmaxY div 4;
x2:=3*x1;
y2:=3*y1;
Rectangle(x1,y1,x2,y2);
SetViewPort(x1+1,y1+1,x2-1,y2-1,clipon);
for k:=1 to N do
with a[k] do
begin
x:=Random(x2-x1);
y:=Random(y2-y1);
end;
repeat
for k:=1 to N do
with a[k] do
PutPixel(x,y,white);
if not KeyPressed then
for k:=N downto 1 do
with a[k] do
putpixel(x,y,black)
until KeyPressed;
{while KeyPressed do k:=ord(readKey);}
CloseGraph
end;
end.