Thuật toán MIDPOInt

uses crt,graph;
var xp,yp,xq,yq:integer;
{----------------------khoi tao do hoa---------------------------- }
procedure Khoitao;
var gd,gm:integer;
Begin
gd:=detect;
initgraph(gd,gm,'d:\tp\bgi');
if graphresult <> grok then
Begin
writeln('Loi khoi tao do hoa, kiem tra lai duong dan');
readln;
halt(1);
End;
End;
{------------Dung Hinh----------------}
procedure DungHinh;
Begin
repeat until keypressed;
End;
{---------ket thuc do hoa----}
procedure Ketthuc;
Begin
closegraph;
End;
{---------Thuat toan ve doan thang DDA hsg <1--}
procedure MidLine(xa,ya,xb,yb,m:integer);
var A,B,x,y: integer;
P:real;
Begin
outtextxy(xa-10,ya,'A');
outtextxy(xb+10,yb,'B');
A:=yb-ya;
B:=-(xb-xa);
P:=A+b/2;
x:=xa;
y:=ya;
Repeat
putpixel(x,y,m);
if P<0 then P:=P+A
else
begin
P:=P+A+B;
y:=y+1;
end;
x:=x+1;
Until x>xb;
End;
{---Bong nay------}
procedure bongnay;
var i:integer;
Begin
for i:=50 to getmaxy-51 do
begin
circle(round(getmaxx/2),i,50);
delay(10);
cleardevice;
end;
for i:=getmaxy-50 downto 50 do
begin
circle(round(getmaxx/2),i,50);
delay(10);
cleardevice;
end;
End;

{-------nhap toa do 1 diem---}
procedure NhapDiem(var x,y:integer;ten:char);
Begin
Writeln('Nhap toa do cho diem ',ten);
write(ten,'(x,y)=');readln(x,y);
End;
{---------------CHUONG TRINH CHINH---------------------}
BEGIN
clrscr;
Nhapdiem(xp,yp,'P');
Nhapdiem(xq,yq,'Q');
khoitao;
MidLine(xp,yp,xq,yq,yellow);
dunghinh;
ketthuc;

END.