uses crt,graphabc;
const N=5;//частота отрисовки
const T=400; //уровень отрисовки
var i,j:integer;
type point=array[1..2] of integer;
type ColorType=integer;

procedure osi;
begin
 setpenwidth(3);
 line(400,0,400,800);
 line(0,400,800,400);
 line(800,0,0,800);
end;

function to2DY(x,y,z:integer):integer;
 begin
  to2DY:=400-z+trunc(0.4*y);
 end;

function to2DX(x,y,z:integer):integer;
 begin
  to2DX:=400+x-trunc(0.4*y);
 end;


procedure setpixel3d(x,y,z:integer);
begin
 setpixel(400+x-trunc(0.4*y),400-z+trunc(0.4*y),clBlack);
end;

procedure line3d(x,y,z,x1,y1,z1:integer);
begin
 line(to2DX(x,y,z),to2Dy(x,y,z),to2DX(x1,y1,z1),to2Dy(x1,y1,z1))
end;

procedure lineto3d(x1,y1,z1:integer);
begin
 lineto(to2DX(x1,y1,z1),to2Dy(x1,y1,z1))
end;

procedure moveto3d(x1,y1,z1:integer);
begin
 moveto(to2DX(x1,y1,z1),to2Dy(x1,y1,z1))
end;

////////////////////////////////////////////////////////
function f(x,y:real):real;
var a:integer;
begin
try
 f:=(x*x-y*y)/1000;   //сама функция двух аргументов
except
 f:=1;
end;
end;
 ///////////////////////////////////////


procedure metka(x1,y1,z1:integer);
var color1:integer;
begin

 color1:=pencolor();
 SetBrushColor(clgreen);
 SetPencolor(clgreen);
 SetBrushStyle(bsSolid);
 circle(to2DX(x1,y1,z1),to2Dy(x1,y1,z1),2);
 SetBrushStyle(bsClear);
 SetpenColor(color1);
end;





procedure draw(F: function(x,y:real):real; color:colortype);
begin
 setpenwidth(1);
 setpencolor(color);
 for j:=-T to T do
 begin
    moveto3d(j,-T,trunc(f(j,-T)));
    for i:=-T to T do
     begin
      if (i mod N=0) and (j mod N=0) then lineto3d(j,i,trunc(f(j,i)));
       if abs(f(j,i))<0.001 then metka(j,i,trunc(f(j,i)));
     end;

 end;
 for i:=-T to T do
 begin
    moveto3d(-T,i,trunc(f(-T,i)));
    for j:=-T to T do
     begin
      if (i mod N=0) and (j mod N=0) then lineto3d(j,i,trunc(f(j,i)));
       if abs(f(j,i))<0.001 then metka(j,i,trunc(f(j,i)));
     end;

 end;
end;
 

 
begin
 setwindowheight(800);
 setwindowwidth(800);
 osi;
 draw(f,rgb(255,0,0));
end.