all about me: create line in pascal

saya akan memberikan tutorial membuat sebuah garis pada pascal dengan menggunakan opengl, jika ingin menggunakan pascal sebaiknya gunakan "freepascal" karena jika kita menginstall freepascal maka kita tidak perlu lagi menambahkan library opengl karena freepascal telah include opengl.

ini adalah coding'a.:

uses graph,crt;
var driver,mode:integer;
x1,y1,x2,y2:integer;
step,k:integer;
dx,dy:real;
xm,ym,x,y:real;
pil :integer;
men:integer;
label menu;

procedure utama;
begin
driver:=detect;
InitGraph(driver,mode,'');
end;

procedure Input;
begin
clrscr;
writeln('Program Menggambar Garis DIAGONAL');
writeln('<<=========================================>>');
writeln;
write('Masukkan Nilai x1: ');
readln(x1);
write('masukan nilai X2: ');
readln(x2);
write('Masukkan Nilai y1: ');
readln(y1);
write('Masukkan Nilai y2: ');
readln(y2);
end;

procedure Garis_diagonal;
begin
x1:=abs(x1);
x2:=abs(x2);
y1:=abs(y1);
y2:=abs(y2);

dx:=x2-x1;
dy:=y2-y1;
x:=x1;
y:=y1;
if abs(dx) > abs(dy) then
step:=round(abs(dx))
else
step:=round(abs(dy));
xm:=dx/step;
ym:=dy/step;
putPixel(round(x),round(y),red);
for k:=1 to step do
begin
x:=x+xm;
y:=y+ym;
putPixel(round(x),round(y),red);
end;
end;

procedure hor;
begin
driver:=detect;
InitGraph(driver,mode,'');
end;

procedure inhor;
begin
clrscr;
writeln('Program Menggambar Garis');
writeln('<<=========================================>>');
writeln;
write('Masukkan Nilai x1: ');
readln(x1);
write('Masukkan Nilai y1: ');
readln(y1);
writeln('Masukan Nilai y2 : ');
readln(y2);

end;

procedure gahor;
begin
x1:=abs(x1);

y1:=abs(y1);
y2:=abs(y2);

dy:=y2-y1;
x:=x1;
y:=y1;
if abs(x) > abs(dy) then
step:=round(abs(x))
else
step:=round(abs(dy));

ym:=dy/step;
putPixel(round(x),round(y),yellow);
for k:=1 to step do
begin

y:=y+ym;
putPixel(round(x),round(y),yellow);
end;
end;

procedure ver;
begin

driver:=detect;
InitGraph(driver,mode,'');
end;

procedure inver;
begin
clrscr;
writeln('Program Menggambar Garis');
writeln('<<=========================================>>');
writeln;
write('Masukkan Nilai x1: ');
readln(x1);
writeln('Masukan Nilai x2: ');
readln(x2);
write('Masukkan Nilai y1: ');
readln(y1);

end;

procedure gaver;
begin
x1:=abs(x1);
x2:=abs(x2);
y1:=abs(y1);
y2:=abs(y2);
dx:=x2-x1;

x:=x1;
y:=y1;
if abs(dx) > abs(y) then
step:=round(abs(dx))
else
step:=round(abs(dy));
xm:=dx/step;

putPixel(round(x),round(y),green);
for k:=1 to step do
begin
x:=x+xm;

putPixel(round(x),round(y),green);
end;
end;

begin
menu:
clrscr;
writeln('-------menu-------');
writeln('==================');
writeln('1. vertikal ');
writeln('2. horizontal ');
writeln('3. diagonal ');
writeln('4. keluar ');
writeln('ukuran layar 1024 x 768 ');
writeln('untuk hasil yang maximal masukan kordinat 100-999');
writeln('masukan pilihan :');
readln(pil);
case pil of
1: begin
   inhor;
   hor;
   gahor;
   goto menu;
   end;

2: begin
inver;
ver;
gaver;
goto menu;
   end;

3: begin
   input;
   utama;
   Garis_diagonal;
   readln;
   goto menu;

end;
4: begin

end;
end;
end.

output: