Starfields

                    嬪様様様様様様様様様様様様様様様
                             W E L C O M E         
                      To the VGA Trainer Program    
                                  By                
                          DENTHOR of ASPHYXIA        
                    塒様様様様様様様様様様様様様様様  
                      陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳 
                        陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳

                            --==[ PART 13 ]==--

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
  Introduction

 Hello again! Here I am, cooped up at home, recovering from my illness
 with nothing to do, so of course it is the perfect time to write another
 trainer! After the long delay between parts 11 and 12, two trainers in
 two days doesn't sound like a bad idea.

 This trainer is on starfields, which is by request of more then one
 person. This is quite an easy effect, and you should have no trouble
 grasping the concept behind it. I will be doing a 3d starfield, a
 horizontal starfield is very easy with you merely incrementing a x-value
 for each star for each frame. I am not even going to bother doing code
 for that one (unless requested).

 So I am off to go grab my antibiotics pills and I will be right back
 with the tutorial! ;-)

 If you would like to contact me, or the team, there are many ways you
 can do it : 1) Write a message to Grant Smith/Denthor/Asphyxia in private mail
                   on the ASPHYXIA BBS.
             2) Write to Denthor, EzE, Goth, Fubar or Nobody on Connectix.
             3) Write to :  Grant Smith
                            P.O.Box 270 Kloof
                            3640
                            Natal
                            South Africa
             4) Call me (Grant Smith) at (031) 73 2129 (leave a message if you
                   call during varsity). Call +27-31-73-2129 if you call
                   from outside South Africa. (It's YOUR phone bill ;-))
             5) Write to smith9@batis.bis.und.ac.za in E-Mail.
             6) Write to asphyxia@beastie.cs.und.ac.za

 NB : If you are a representative of a company or BBS, and want ASPHYXIA
        to do you a demo, leave mail to me; we can discuss it.
 NNB : If you have done/attempted a demo, SEND IT TO ME! We are feeling
         quite lonely and want to meet/help out/exchange code with other demo
         groups. What do you have to lose? Leave a message here and we can work
         out how to transfer it. We really want to hear from you!

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   What is a 3d starfield?

 I am not even sure if I should do this bit. Go watch any episode of Star
 Trek, the movies, Star Wars, or just about any sci-fi movie. Somewhere
 there will be a scene where you can see stars whizzing past the
 viewscreen, with the ones that are further away moving slower then the
 ones that are passed quite close to.

 This is a 3d starfield. If you look closely, you will see that all the
 stars seem to originate from a point, the point you are travelling
 towards.  This is an illusion which thankfully happens automatically,
 you don't have to code for it ;)

 Starfields look very nice, and can make a big difference to an otherwise
 black background. It also makes a great screen saver ;-)

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   How do they work?

 This is actually quite simple. Imagine if you will, each star in the
 heavens having an x,y and z coordinate, with you being at 0,0,0. Easy?
 Right. Now, if you were to say move forward, ie. increase your z value,
 to you you will still be at 0,0,0 , but all the stars z values would
 have appeared to decrease by the exact same amount.

 In easier language, we decrease the z value of all the the stars so that
 they come closer to you, and eventually whizz past.

 This solves all our problems. Stars that are close to us on the x and y
 scales will pass us by faster then those that are very far from us on
 the x and y scales. The only thing we must watch out for is that no star
 is at 0,0 , ie. exactly in front of us, otherwise there will be a
 collision which will not look good.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   How do we code this?

 The first thing to be done is to generate our starfield. This is quite
 easy, with us choosing x values between -160 and 160, and y values
 between -100 and 100 randomly. Each z is sequentially greater for each
 star so that we don't get large areas with no stars. We must remember to
 check that there are no stars at 0,0!

 Okay, now we start the actual viewing section. Here are the steps :

 1) Convert our 3-d coords into their 2-d versions. Have a look at tut 8
    to see how this is done, but basically we divide by z.

 2) Clear away all old stars that may be on the screen.

 3) Draw all our stars according to our 2-d values we have calculated in
    1)

 4) Move all the stars either closer to us or further away from us by
    decreasing or increasing their z values respectively.

 5) If a star's z value has passed into the negative, place it at the
    very back of our "queue" so that it will come around again

 6) Jump back to 1) ad-infinitum.

 That is, as they say, it. In our sample program the steps have been
 neatly placed into individual procedures for easy reading.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   What next?

 Okay, so now we have a cool looking starfield. What next? How about
 adding left and right motion? A menu or a scrolly in the foreground? How
 about figuring out how a star tunnel works? A cool 3d routine going in
 front of the stars?

 A starfield can make just about any routine look just that much more
 professional, and can itself be improved to be a great effect all on
 it's own.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   In closing

 So, this was yet another effect in the series. Do you still want more
 effects, or what? Leave me mail with further ideas for trainers. I may
 not do it if you don't ask for it!

 Oh, well, the medicine has been taken, it is time for me to go. Hello to
 all those people who have sent me mail, and those great guys on #coders
 in IRC (you know who you are). Wow. That is the first greets I have ever
 done in a trainer. Hmm. Maybe I'm just ill ;-)

 Happy coding people!
   - Denthor
       19:28
         24-7-94

 The following are official ASPHYXIA distribution sites :

 浜様様様様様様様様様様様様曜様様様様様様様様僕様様
 BBS Name                  Telephone No.   Open 
 麺様様様様様様様様様様様様洋様様様様様様様様陵様様
 ASPHYXIA BBS #1           +27-31-765-5312 ALL  
 ASPHYXIA BBS #2           +27-31-765-6293 ALL  
 C-Spam BBS                410-531-5886    ALL  
 Connectix BBS             +27-31-266-9992 ALL  
 POP!                      +27-12-661-1257 ALL  
 Soul Asylum               +358-0-5055041  ALL  
 Wasted Image              407-838-4525    ALL  
 藩様様様様様様様様様様様様擁様様様様様様様様瞥様様

 Leave me mail if you want to become an official Asphyxia BBS
 distribution site.

 Unit GFX2;

 INTERFACE

 USES crt;
 CONST VGA = $A000;

 TYPE Virtual = Array [1..64000] of byte;  { The size of our Virtual Screen }
      VirtPtr = ^Virtual;                  { Pointer to the virtual screen }

 VAR Virscr : VirtPtr;                     { Our first Virtual screen }
     Vaddr  : word;                        { The segment of our virtual screen}

 Procedure SetMCGA;
    { This procedure gets you into 320x200x256 mode. }
 Procedure SetText;
    { This procedure returns you to text mode.  }
 Procedure Cls (Where:word;Col : Byte);
    { This clears the screen to the specified color }
 Procedure SetUpVirtual;
    { This sets up the memory needed for the virtual screen }
 Procedure ShutDown;
    { This frees the memory used by the virtual screen }
 procedure flip(source,dest:Word);
    { This copies the entire screen at "source" to destination }
 Procedure Pal(Col,R,G,B : Byte);
    { This sets the Red, Green and Blue values of a certain color }
 Procedure GetPal(Col : Byte; Var R,G,B : Byte);
   { This gets the Red, Green and Blue values of a certain color }
 procedure WaitRetrace;
    {  This waits for a vertical retrace to reduce snow on the screen }
 Procedure Hline (x1,x2,y:word;col:byte;where:word);
    { This draws a horizontal line from x1 to x2 on line y in color col }
 Procedure Line(a,b,c,d:integer;col:byte;where:word);
   { This draws a solid line from a,b to c,d in colour col }
 Procedure DrawPoly(x1,y1,x2,y2,x3,y3,x4,y4:integer;color:byte;where:word);
    { This draw a polygon with 4 points at x1,y1 , x2,y2 , x3,y3 , x4,y4
      in color col }
 Function rad (theta : real) : real;
    {  This calculates the degrees of an angle }
 Procedure Putpixel (X,Y : Integer; Col : Byte; where:word);
    { This puts a pixel on the screen by writing directly to memory. }
 Function Getpixel (X,Y : Integer; where:word) :Byte;
    { This gets the pixel on the screen by reading directly to memory. }
 Procedure LoadCEL (FileName :  string; ScrPtr : pointer);
   { This loads the cel 'filename' into the pointer scrptr }

 IMPLEMENTATION

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure SetMCGA;  { This procedure gets you into 320x200x256 mode. }
 BEGIN
   asm
      mov        ax,0013h
      int        10h
   end;
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure SetText;  { This procedure returns you to text mode.  }
 BEGIN
   asm
      mov        ax,0003h
      int        10h
   end;
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure Cls (Where:word;Col : Byte); assembler;
    { This clears the screen to the specified color }
 asm
    push    es
    mov     cx, 32000;
    mov     es,[where]
    xor     di,di
    mov     al,[col]
    mov     ah,al
    rep     stosw
    pop     es
 End;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure SetUpVirtual;
    { This sets up the memory needed for the virtual screen }
 BEGIN
   GetMem (VirScr,64000);
   vaddr := seg (virscr^);
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure ShutDown;
    { This frees the memory used by the virtual screen }
 BEGIN
   FreeMem (VirScr,64000);
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 procedure flip(source,dest:Word); assembler;
   { This copies the entire screen at "source" to destination }
 asm
   push    ds
   mov     ax, [Dest]
   mov     es, ax
   mov     ax, [Source]
   mov     ds, ax
   xor     si, si
   xor     di, di
   mov     cx, 32000
   rep     movsw
   pop     ds
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure Pal(Col,R,G,B : Byte); assembler;
   { This sets the Red, Green and Blue values of a certain color }
 asm
    mov    dx,3c8h
    mov    al,[col]
    out    dx,al
    inc    dx
    mov    al,[r]
    out    dx,al
    mov    al,[g]
    out    dx,al
    mov    al,[b]
    out    dx,al
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure GetPal(Col : Byte; Var R,G,B : Byte);
   { This gets the Red, Green and Blue values of a certain color }
 Var
    rr,gg,bb : Byte;
 Begin
    asm
       mov    dx,3c7h
       mov    al,col
       out    dx,al

       add    dx,2

       in     al,dx
       mov    [rr],al
       in     al,dx
       mov    [gg],al
       in     al,dx
       mov    [bb],al
    end;
    r := rr;
    g := gg;
    b := bb;
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 procedure WaitRetrace; assembler;
   {  This waits for a vertical retrace to reduce snow on the screen }
 label
   l1, l2;
 asm
     mov dx,3DAh
 l1:
     in al,dx
     and al,08h
     jnz l1
 l2:
     in al,dx
     and al,08h
     jz  l2
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure Hline (x1,x2,y:word;col:byte;where:word); assembler;
   { This draws a horizontal line from x1 to x2 on line y in color col }
 asm
   mov   ax,where
   mov   es,ax
   mov   ax,y
   mov   di,ax
   shl   ax,8
   shl   di,6
   add   di,ax
   add   di,x1

   mov   al,col
   mov   ah,al
   mov   cx,x2
   sub   cx,x1
   shr   cx,1
   jnc   @start
   stosb
 @Start :
   rep   stosw
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure Line(a,b,c,d:integer;col:byte;where:word);
   { This draws a solid line from a,b to c,d in colour col }
   function sgn(a:real):integer;
   begin
        if a>0 then sgn:=+1;
        if a<0 then sgn:=-1;
        if a=0 then sgn:=0;
   end;
 var i,s,d1x,d1y,d2x,d2y,u,v,m,n:integer;
 begin
      u:= c - a;
      v:= d - b;
      d1x:= SGN(u);
      d1y:= SGN(v);
      d2x:= SGN(u);
      d2y:= 0;
      m:= ABS(u);
      n := ABS(v);
      IF NOT (M>N) then
      BEGIN
           d2x := 0 ;
           d2y := SGN(v);
           m := ABS(v);
           n := ABS(u);
      END;
      s := m shr 1;
      FOR i := 0 TO m DO
      BEGIN
           putpixel(a,b,col,where);
           s := s + n;
           IF not (smxy then mxy:=y2;
   if y3mxy then mxy:=y3;    { Choose the min y mny and max y mxy }
   if y4mxy then mxy:=y4;

   if mny<0 then mny:=0;
   if mxy>199 then mxy:=199;
   if mny>199 then exit;
   if mxy<0 then exit;        { Verticle range checking }

   mul1:=x1-x4; div1:=y1-y4;
   mul2:=x2-x1; div2:=y2-y1;
   mul3:=x3-x2; div3:=y3-y2;
   mul4:=x4-x3; div4:=y4-y3;  { Constansts needed for intersection calc }

   for yc:=mny to mxy do
     begin
       mnx:=320;
       mxx:=-1;
       if (y4>=yc) or (y1>=yc) then
         if (y4<=yc) or (y1<=yc) then   { Check that yc is between y1 and y4 }
           if not(y4=y1) then
             begin
               x:=(yc-y4)*mul1 div div1+x4; { Point of intersection on x axis }
               if xmxx then
                 mxx:=x;       { Set point as start or end of horiz line }
             end;
       if (y1>=yc) or (y2>=yc) then
         if (y1<=yc) or (y2<=yc) then   { Check that yc is between y1 and y2 }
           if not(y1=y2) then
             begin
               x:=(yc-y1)*mul2 div div2+x1; { Point of intersection on x axis }
               if xmxx then
                 mxx:=x;       { Set point as start or end of horiz line }
             end;
       if (y2>=yc) or (y3>=yc) then
         if (y2<=yc) or (y3<=yc) then   { Check that yc is between y2 and y3 }
           if not(y2=y3) then
             begin
               x:=(yc-y2)*mul3 div div3+x2; { Point of intersection on x axis }
               if xmxx then
                 mxx:=x;       { Set point as start or end of horiz line }
             end;
       if (y3>=yc) or (y4>=yc) then
         if (y3<=yc) or (y4<=yc) then   { Check that yc is between y3 and y4 }
           if not(y3=y4) then
             begin
               x:=(yc-y3)*mul4 div div4+x3; { Point of intersection on x axis }
               if xmxx then
                 mxx:=x;       { Set point as start or end of horiz line }
             end;
       if mnx<0 then
         mnx:=0;
       if mxx>319 then
         mxx:=319;          { Range checking on horizontal line }
       if mnx<=mxx then
         hline (mnx,mxx,yc,color,where);   { Draw the horizontal line }
     end;
   end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Function rad (theta : real) : real;
   {  This calculates the degrees of an angle }
 BEGIN
   rad := theta * pi / 180
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure Putpixel (X,Y : Integer; Col : Byte; where:word); assembler;
   { This puts a pixel on the screen by writing directly to memory. }
 Asm
   mov     ax,[where]
   mov     es,ax
   mov     bx,[X]
   mov     dx,[Y]
   mov     di,bx
   mov     bx, dx                  {; bx = dx}
   shl     dx, 8
   shl     bx, 6
   add     dx, bx                  {; dx = dx + bx (ie y*320)}
   add     di, dx                  {; finalise location}
   mov     al, [Col]
   stosb
 End;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Function Getpixel (X,Y : Integer; where:word):byte; assembler;
   { This puts a pixel on the screen by writing directly to memory. }
 Asm
   mov     ax,[where]
   mov     es,ax
   mov     bx,[X]
   mov     dx,[Y]
   mov     di,bx
   mov     bx, dx                  {; bx = dx}
   shl     dx, 8
   shl     bx, 6
   add     dx, bx                  {; dx = dx + bx (ie y*320)}
   add     di, dx                  {; finalise location}
   mov     al, es:[di]
 End;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure LoadCEL (FileName :  string; ScrPtr : pointer);
   { This loads the cel 'filename' into the pointer scrptr }
 var
   Fil : file;
   Buf : array [1..1024] of byte;
   BlocksRead, Count : word;
 begin
   assign (Fil, FileName);
   reset (Fil, 1);
   BlockRead (Fil, Buf, 800);    { Read and ignore the 800 byte header }
   Count := 0; BlocksRead := $FFFF;
   while (not eof (Fil)) and (BlocksRead <> 0) do begin
     BlockRead (Fil, mem [seg (ScrPtr^): ofs (ScrPtr^) + Count], 1024, BlocksRead);
     Count := Count + 1024;
   end;
   close (Fil);
 end;

 BEGIN
 END.{$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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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 ('    smith9@batis.bis.und.ac.za');
   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.

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Date this article was posted to GameDev.net: 7/16/1999
(Note that this date does not necessarily correspond to the date the article was written)

See Also:
Denthor's Asphyxia Tutorials

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