Vi du 2 :

Program Cong_bac_3;

USES graph,crt;

VAR

pi:array[0..3] of real;

u: real;

xi,yi:array[0..3,0..3]of real;

x,y:array[0..3]of real;

m,n:array[0..100]of real;

xdau,Gd,Gm,t,i,j,k,l:integer;

a1,b1,c,s:real;

f:text;

(*************************************************)

{-------------Ve he truc toa do------------}

procedure khoitao;

begin

Gd := Detect;

InitGraph(Gd, Gm, 'c:\tp\bgi ');

if GraphResult <> grOk then Halt(1);

directvideo:=False;

setbkcolor(1);

setcolor(14);

setviewport(getmaxX div 2,getmaxY div 2,getmaxX,getmaxY,false);

line(-320,0,319,0);

line(319,0,310,-5);

line(319,0,310,5);

line(0,239,0,-240);

line(-5,-230,0,-240);

line(5,-230,0,-240);

outtextxy(-10,-10,'O');

outtextxy(305,10,'x');

outtextxy(10,-230,'y');

end;

(*************************************************)

{thu tuc ve duong cong tron theo thuat toan CASTELJAU}

PROCEDURE ve;

Var

i,j : integer;

BEGIN

moveto(round(x[0]),round(y[0]));

for i:=0 to 3 do

Begin

yi[i,0]:=y[i];

xi[i,0]:=x[i];

End;

u:=0;

while u<=1 do

Begin

for j:=1 to 3 do

Begin

for i:=j to 3 do

Begin

xi[i,j]:=(1-u)*xi[i-1,j-1]+u*xi[i,j-1];

yi[i,j]:=(1-u)*yi[i-1,j-1]+u*yi[i,j-1];

End;

End;

{lineto(round(xi[i,j]),round(yi[i,j]));}

putpixel(round(xi[i,j]),round(yi[i,j]),WHITE);

delay(0);

u:=u+0.0001

End; END;

(*************************************************)

{-------------Chuong Trinh Chinh------------}

BEGIN

l:=6; {l phai la so chan}

m[0]:=-90; n[0]:=100;

m[1]:=-60; n[1]:=60;

m[2]:=-40; n[2]:=80;

m[3]:=0; n[3]:=10;

m[4]:=60; n[4]:=140;

m[5]:=160; n[5]:=120;

m[6]:=260; n[6]:=220;

khoitao;

i:=0;

x[0]:=m[i];

y[0]:=n[i];

i:=i+1;

x[2]:=m[i];

y[2]:=n[i];

circle(round(x[2]),round(y[2]),2);

x[1]:=x[2]-5;

y[1]:=y[2]-5;

i:=i+1;

x[3]:=m[i];

y[3]:=n[i];

x[2]:=(8*x[2]-x[0]-3*x[1]-x[3])/3;

y[2]:=(8*y[2]-y[0]-3*y[1]-y[3])/3;

circle(round(x[0]),round(y[0]),2);

circle(round(x[3]),round(y[3]),2);

ve;

while i<l do

Begin

x[0]:=x[3];y[0]:=y[3];

x[1]:=x[3]+(x[3]-x[2]);

y[1]:=y[3]+(y[3]-y[2]);

i:=i+1;

x[2]:=m[i];

y[2]:=n[i];

circle(round(x[2]),round(y[2]),2);

i:=i+1;

x[3]:=m[i];

y[3]:=n[i];

x[2]:=(8*x[2]-x[0]-3*x[1]-x[3])/3;

y[2]:=(8*y[2]-y[0]-3*y[1]-y[3])/3;

circle(round(x[0]),round(y[0]),2);

circle(round(x[3]),round(y[3]),2);

ve;

End;

repeat until

keypressed;

closegraph;

END.