{$X+}
USES GFX2,crt;

CONST Num = 400;     { Number of stars }

TYPE Star = Record
              x,y,z:integer;
            End;     { Information on each star }
     Pos = Record
             x,y:integer;
           End;      { Information on each point to be plotted }

VAR Stars : Array [1..num] of star;
    Clear : Array [1..2,1..num] of pos;

{ִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִ}
Procedure Init;
VAR loop1,loop2:integer;
    logo:array [1..50,1..320] of byte;
BEGIN
  for loop1:=1 to num do
    Repeat
      stars[loop1].x:=random (320)-160;
      stars[loop1].y:=random (200)-100;
      stars[loop1].z:=loop1;
    Until (stars[loop1].x<>0) and (stars[loop1].y<>0);
      { Make sure no stars are heading directly towards the viewer }
  pal (32,00,00,30);
  pal (33,10,10,40);
  pal (34,20,20,50);
  pal (35,30,30,60);   { Pallette for the stars coming towards you }

  pal (247,20,20,20);
  pal (136,30,0 ,0 );
  pal (101,40,0 ,0 );
  pal (19 ,60,0 ,0 );  { Pallette for the logo at the top of the screen }

  loadcel ('logo.cel',addr(logo));
  for loop1:=0 to 319 do
    for loop2:=1 to 50 do
      putpixel (loop1,loop2-1,logo[loop2,loop1+1],vga);
    { Placing the logo at the top of the screen }
END;

{ִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִ}
Procedure Calcstars;
  { This ccalculates the 2-d coordinates of our stars and saves these values
    into the variable clear }
VAR loop1,x,y:integer;
BEGIN
  For loop1:=1 to num do BEGIN
    x:=((stars[loop1].x shl 7) div stars[loop1].z)+160;
    y:=((stars[loop1].y shl 7) div stars[loop1].z)+100;
    clear[1,loop1].x:=x;
    clear[1,loop1].y:=y;
  END;
END;

{ִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִ}
Procedure Drawstars;
  { This draws the 2-d values stored in clear to the vga screen, with various
    colors according to how far away it is. }
VAR loop1,x,y:integer;
BEGIN
  For loop1:=1 to num do BEGIN
    x:=clear[1,loop1].x;
    y:=clear[1,loop1].y;
    if (x>0) and (x<320) and (y>50) and (y<200) then
      If stars[loop1].z>400 then putpixel(x,y,32,vga)
      else
      If stars[loop1].z>300 then putpixel(x,y,33,vga)
      else
      If stars[loop1].z>200 then putpixel(x,y,34,vga)
      else
      If stars[loop1].z>100 then putpixel(x,y,34,vga)
      else
      putpixel(x,y,35,vga)
  END;
END;

{ִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִ}
Procedure Clearstars;
  { This clears the 2-d values from the vga screen, which is faster then a
    cls (vga,0) }
VAR loop1,x,y:integer;
BEGIN
  For loop1:=1 to num do BEGIN
    x:=clear[2,loop1].x;
    y:=clear[2,loop1].y;
    if (x>0) and (x<320) and (y>50) and (y<200) then
      putpixel (x,y,0,vga);
  END;
END;


{ִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִ}
Procedure MoveStars (Towards:boolean);
  { If towards is True, then the z-value of each star is decreased to come
    towards the viewer, otherwise the z-value is increased to go away from
    the viewer }
VAR loop1:integer;
BEGIN
  If towards then
    for loop1:=1 to num do BEGIN
      stars[loop1].z:=stars[loop1].z-2;
      if stars[loop1].z<1 then stars[loop1].z:=stars[loop1].z+num;
    END
    else
    for loop1:=1 to num do BEGIN
      stars[loop1].z:=stars[loop1].z+2;
      if stars[loop1].z>num then stars[loop1].z:=stars[loop1].z-num;
    END;
END;

{ִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִִ}
Procedure Play;
  { This is our main procedure }
VAR ch:char;
BEGIN
  Calcstars;
  Drawstars;  { This draws our stars for the first time }
  ch:=#0;
  Repeat
    if keypressed then ch:=readkey;
    clear[2]:=clear[1];
    Calcstars;     { Calculate new star positions }
    waitretrace;
    Clearstars;    { Erase old stars }
    Drawstars;     { Draw new stars }
    if ch=' ' then Movestars(False) else Movestars(True);
      { Move stars towards or away from the viewer }
  Until ch=#27;
    { Until the escape key is pressed }
END;

BEGIN
  clrscr;
  writeln ('Hello! Another effect for you, this one is on starfields, again by');
  writeln ('request.  In this sample program, a starfield will be coming towards');
  writeln ('you. Hit the space bar to have it move away from you, any other key');
  writeln ('to have it come towards you again. Hit [ESC] to end.');
  writeln;
  Writeln ('The logo at the top of the screen was drawn by me in Autodesk Animator.');
  Writeln ('It only took a few seconds, so please don''t laugh too much at my attempt.');
  writeln;
  writeln ('The code is very easy to follow, and the documentation is as usual in the');
  writeln ('main text. Leave me mail with further ideas for future trainers.');
  writeln;
  writeln;
  write ('Hit any key to continue ...');
  readkey;
  randomize;
  setmcga;
  init;
  Play;
  settext;
  Writeln ('All done. This concludes the thirteenth sample program in the ASPHYXIA');
  Writeln ('Training series. You may reach DENTHOR under the names of GRANT');
  Writeln ('SMITH/DENTHOR/ASPHYXIA on the ASPHYXIA BBS. I am also an avid');
  Writeln ('Connectix BBS user, and occasionally read RSAProg. E-mail me at :');
  Writeln ('    [email protected]');
  Writeln ('The numbers are available in the main text. You may also write to me at:');
  Writeln ('             Grant Smith');
  Writeln ('             P.O. Box 270');
  Writeln ('             Kloof');
  Writeln ('             3640');
  Writeln ('             Natal');
  Writeln ('             South Africa');
  Writeln ('I hope to hear from you soon!');
  Writeln; Writeln;
  Write   ('Hit any key to exit ...');
  readkey;
END.