Алгоритм Брезенхема

uses graphabc;
 
const xx=20;
      yy=20;
      _x=100;
      _y=310;
      
procedure drawLine(x1,y1,x2,y2:integer);
var x,y, delta,dx,dy,d,d1,d2:integer;
begin
dx:=x2-x1;
dy:=y2-y1;
d:=2*dy-dx;
x:=x1;
y:=y1;
 
repeat
      setpixel(x,y,clred);
      if d<0 then delta:=2*dy else begin
         delta:=2*(dy-dx);
         y:=y+1;
      end;
      delta:=d+delta;
      x:=x+1;
until x>x2;
 
end;
begin
drawLine(xx,yy,_x,_y);
line(xx,yy+10,_x,_y+10);
end.

uses graphABC;
procedure drawLine(x1, y1, x2, y2: integer);
var
  currentX, currentY: integer;
  errorX, errorY: integer;
  d, dx, dy, incX, incY: integer;
begin
  dx := x2 - x1;
  dy := y2 - y1;
  errorX := 0;
  errorY := 0;
 
  if(dx > 0) then incX := 1
    else if(dx = 0) then incX := 0
      else incX := -1;
 
  if(dy > 0) then incY := 1
    else if(dy = 0) then incY := 0
      else incY := -1;
 
  dx := abs(dx);
  dy := abs(dy);
 
  if(dy > dx) then d := dy
    else d := dx;
 
  currentX := x1;
  currentY := y1;
  SetPixel(currentX, currentY, 0);
  while((currentX <> x2) OR (currentY <> y2)) do
  begin
    errorX := errorX + dx;
    errorY := errorY + dy;
    if(errorX >= d) then
    begin
         errorX := errorX - d;
         currentX := currentX + incX;
    end;
    if(errorY >= d) then
    begin
         errorY := errorY - d;
         currentY := currentY + incY;
    end;
    SetPixel(currentX, currentY, 0);
  end;
end;
begin
setpencolor(clBlue);
drawLine(10,50,50,400);
setpencolor(clRed);
line(10,50,50,400)
end.