program midpoint;

uses crt,graph;

var xMax,i,gd,gm,r,x,y:integer; ym:real;

p:real;

procedure veduongtron(x1,y1,r:integer);

procedure put8pixel(x1,y1,x,y,m:integer);

Begin

putpixel(x1+x,y1+y,m);

putpixel(x1+x,y1-y,m);

putpixel(x1-x,y1+y,m);

putpixel(x1-x,y1-y,m);

putpixel(x1+y,y1+x,m);

putpixel(x1+y,y1-x,m);

putpixel(x1-y,y1+x,m);

putpixel(x1-y,y1-x,m);

end;

    Begin

    p:=(5/4)-r;

    x:=0;y:=r;

    put8pixel(x1,y1,x,y,10);

    while (x<y) do

    Begin

    if(p<0) then

             p:=p+2*x+3

    else

        Begin p:=p+2*(x-y)+5;

              y:=y-1;

        end;

    x:=x+1;

    put8pixel(x1,y1,x,y,10);

    End;

    End;

    Begin

    gd:=0;

    initgraph(gd,gm,'D:\Turbo Pascal 7.0');

    x:=100; ym:=getmaxy/2; y:=round(ym);

    xMax:=getmaxX;

    repeat

    for i:=0 to 50 do

    Begin

    x:=x+i;

    veduongtron(300,250,x);

    clearviewport;

    end;

     for i:=50 downto 0 do

    Begin

    x:=x+i;

    veduongtron(300,250,x);

    clearviewport;

    end;

    until keypressed;

    readln;

    closegraph;

End.