Hi there again! This is Grant Smith, AKA Denthor of ASPHYXIA. This is the second part of my Training Program for new programmers. I have only had a lukewarm response to my first part of the trainer series …

remember, if I don't hear from you, I will assume that you are all dead and will stop writing the series .

Also, if you do get in contact with me I will give you some of our fast assembly routines which will speed up your demos no end. So go on, leave mail to GRANT SMITH in the main section of the MailBox BBS, start up a discussion or ask a few questions in this Conference, leave mail to ASPHYXIA on the ASPHYXIA BBS, leave mail to Denthor on Connectix, or write to

Grant Smith,
P.O.Box 270
Kloof
3640

See, there are many ways you can get in contact with me! Use one of them!

In this part, I will put the Pallette through it's paces. What the hell is a pallette? How do I find out what it is? How do I set it? How do I stop the “fuzz” that appears on the screen when I change the pallette? How do I black out the screen using the pallette? How do I fade in a screen? How do I fade out a screen? Why are telephone calls so expensive?

Most of these quesions will be answered in this, the second part of my Trainer Series for Pascal.

A few weeks ago a friend of mine was playing a computer game. In the game there was a machine with stripes of blue running across it. When the machine was activated, while half of the the blue stripes stayed the same, the other half started to change color and glow. He asked me how two stripes of the same color suddenly become different like that. The answer is simple:

the program was changing the palette. As you know from Part 1, there are 256 colors in MCGA mode, numbered 0 to 255.

What you don't know is that each if those colors is made up of different intensities of Red, Green and Blue, the primary colors (you should have learned about the primary colors at school).

These intensities are numbers between 0 and 63. The color of bright red would for example be obtained by setting red intensity to 63, green intensity to 0, and blue intensity to 0.

This means that two colors can look exactly the same, eg you can set color 10 to bright red and color 78 to color bright red.

If you draw a picture using both of those colors, no-one will be able to tell the difference between the two..

It is only when you again change the palette of either of them will they be able to tell the difference.

Also, by changing the whole palette, you can obtain the “Fade in” and “Fade out” effects found in many demos and games.

Palette manipulation can become quite confusing to some people, because colors that look the same are in fact totally separate.

This is very easy to do. To read in the pallette value, you enter in the number of the color you want into port '$3c7', then read in the values of red, green and blue respectively from port '$3c9'. Simple, huh? Here is a procedure that does it for you :

Procedure GetPal(ColorNo : Byte; Var R,G,B : Byte);
  { This reads the values of the Red, Green and Blue values of a certain
    color and returns them to you. }
Begin
   Port[$3c7] := ColorNo;
   R := Port[$3c9];
   G := Port[$3c9];
   B := Port[$3c9];
End;

This is also as easy as 3.1415926535897932385. What you do is you enter in the number of the color you want to change into port '$3c8', then enter the values of red, green and blue respectively into port '$3c9'. Because you are all so lazy I have written the procedure for you

Procedure Pal(ColorNo : Byte; R,G,B : Byte);
  { This sets the Red, Green and Blue values of a certain color }
Begin
   Port[$3c8] := ColorNo;
   Port[$3c9] := R;
   Port[$3c9] := G;
   Port[$3c9] := B;
End;

Asphyxia doesn't use the above pallete procedures, we use assembler versions, which will be given to PEOPLE WHO RESPOND TO THIS TRAINER SERIES (HINT, HINT)

If you have used the pallette before, you will have noticed that there is quite a bit of “fuzz” on the screen when you change it.

The way we counter this is as follows : There is an elctron beam on your monitor that is constantly updating your screen from top to bottom. As it gets to the bottom of the screen, it takes a while for it to get back up to the top of the screen to start updating the screen again. The period where it moves from the bottom to the top is called the Verticle Retrace. During the verticle retrace you may change the pallette without affecting what is on the screen. What we do is that we wait until a verticle retrace has started by calling a certain procedure; this means that everything we do now will only be shown after the verticle retrace, so we can do all sorts of strange and unusual things to the screen during this retrace and only the results will be shown when the retrace is finished. This is way cool, as it means that when we change the pallette, the fuzz doesn't appear on the screen, only the result (the changed pallette), is seen after the retrace! Neat, huh? I have put the purely assembler WaitRetrace routine in the sample code that follows this message. Use it wisely, my son.

This is basic : just set the Red, Green and Blue values of all colors to zero intensity, like so :

Procedure Blackout;
  { This procedure blackens the screen by setting the pallette values ofall the colors to zero. }
VAR loop1:integer;
BEGIN
  WaitRetrace;
  For loop1:=0 to 255 do
    Pal (loop1,0,0,0);
END;

Okay, this can be VERY effective. What you must first do is grab the pallette into a variable, like so :

   VAR Pall := Array [0.255,1..3] of BYTE;

0 to 255 is for the 256 colors in MCGA mode, 1 to 3 is red, green and blue intensity values;

Procedure GrabPallette;
VAR loop1:integer;
BEGIN
  For loop1:=0 to 255 do
    Getpal (loop1,pall[loop1,1],pall[loop1,2],pall[loop1,3]);
END;

This loads the entire pallette into variable pall. Then you must blackout the screen (see above), and draw what you want to screen without the construction being shown. Then what you do is go throgh the pallette. For each color, you see if the individual intensities are what they should be.

If not, you increase them by one unit until they are. Beacuse intensites are in a range from 0 to 63, you only need do this a maximum of 64 times.

Procedure Fadeup;
VAR loop1,loop2:integer;
    Tmp : Array [1..3] of byte;
      { This is temporary storage for the values of a color }
BEGIN
  For loop1:=1 to 64 do BEGIN
      { A color value for Red, green or blue is 0 to 63, so this loop only need be executed a maximum of 64 times }
    WaitRetrace;
    For loop2:=0 to 255 do BEGIN
      Getpal (loop2,Tmp[1],Tmp[2],Tmp[3]);
      If Tmp[1]<Pall[loop2,1] then inc (Tmp[1]);
      If Tmp[2]<Pall[loop2,2] then inc (Tmp[2]);
      If Tmp[3]<Pall[loop2,3] then inc (Tmp[3]);
        { If the Red, Green or Blue values of color loop2 are less then they should be, increase them by one. }
      Pal (loop2,Tmp[1],Tmp[2],Tmp[3]);
        { Set the new, altered pallette color. }
    END;
  END;
END;

Hey-presto! The screen fades up. You can just add in a delay before the waitretrace if you feel it is too fast. Cool, no?

This is just like the fade in of a screen, just in the opposite direction.

What you do is you check each color intensity. If it is not yet zero, you decrease it by one until it is. BAAASIIIC!

Procedure FadeDown;
VAR loop1,loop2:integer;
    Tmp : Array [1..3] of byte;
      { This is temporary storage for the values of a color }
BEGIN
  For loop1:=1 to 64 do BEGIN
    WaitRetrace;
    For loop2:=0 to 255 do BEGIN
      Getpal (loop2,Tmp[1],Tmp[2],Tmp[3]);
      If Tmp[1]>0 then dec (Tmp[1]);
      If Tmp[2]>0 then dec (Tmp[2]);
      If Tmp[3]>0 then dec (Tmp[3]);
        { If the Red, Green or Blue values of color loop2 are not yet zero,
          then, decrease them by one. }
      Pal (loop2,Tmp[1],Tmp[2],Tmp[3]);
        { Set the new, altered pallette color. }
    END;
  END;
END;

Again, to slow the above down, put in a delay above the WaitRetrace. Fading out the screen looks SO much more impressive then just clearing the screen; it can make a world of difference in the impression your demo etc will leave on the people viewing it. To restore the pallette, just do this :

Procedure RestorePallette;
VAR loop1:integer;
BEGIN
  WaitRetrace;
  For loop1:=0 to 255 do
    pal (loop1,Pall[loop1,1],Pall[loop1,2],Pall[loop1,3]);
END;

Well, there are most of those origional questions answered The following sample program is quite big, so it might take you a while to get around it.

Persevere and thou shalt overcome. Pallette manipulation has been a thorn in many coders sides for quite some time, yet hopefully I have shown you all how amazingly simple it is once you have grasped the basics.

I need more feedback! In which direction would you like me to head? Is there any particular section you would like more info on? Also, upload me your demo's, however trivial they might seem. We really want to get in contact with/help out new and old coders alike, but you have to leave us that message telling us about yourself and what you have done or want to do.

IS THERE ANYBODY OUT THERE!?!

P.S. Our new demo should be out soon … it is going to be GOOOD … keep an eye out for it.

And so she came across him, slumped over his keyboard yet again.  
'It's three in the morning' she whispered. 'Let's get you to bed'. 
He stirred, his face bathed in the dull light of his monitor. He mutters something.  
As she leans across him to disconnect the power, she asks him; 'Was it worth it?'.  
His answer surprises her.   
'No.' he says. In his caffiene-enduced haze, he smiles. 'But it sure is a great way to relax.'  

Grant Smith Tue 13 July, 1993, 2:23 am.

See you next week! Denthor

(*****************************************************************************)
(*                                                                           *)
(* TUTPROG2.PAS - VGA Trainer Program 2 (in Pascal)                          *)
(*                                                                           *)
(* "The VGA Trainer Program" is written by Denthor of Asphyxia.  However it  *)
(* was limited to Pascal only in its first run.  All I have done is taken    *)
(* his original release, translated it to C++, and touched up a few things.  *)
(* I take absolutely no credit for the concepts presented in this code, and  *)
(* am NOT the person to ask for help if you are having trouble.              *)
(*                                                                           *)
(* Program Notes : This program presents many new concepts, including:       *)
(*                 line drawing, pallette manipulation, and fading.          *)
(*                 the computer into graphics mode, testing out two differ-  *)
(*                 ent methods of putting pixels to the screen, and finally  *)
(*                 re-entering text mode.                                    *)
(*                                                                           *)
(* Author        : Grant Smith (Denthor)  - denthor@beastie.cs.und.ac.za     *)
(*                                                                           *)
(*****************************************************************************)
 
{$X+}
 
Uses Crt;
 
CONST VGA=$a000;
 
Var Pall,Pall2 : Array[0..255,1..3] of Byte;
     { This declares the PALL variable. 0 to 255 signify the colors of the
       pallette, 1 to 3 signifies the Red, Green and Blue values. I am
       going to use this as a sort of "virtual pallette", and alter it
       as much as I want, then suddenly bang it to screen. Pall2 is used
       to "remember" the origional pallette so that we can restore it at
       the end of the program. }
 
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure SetMCGA;  { This procedure gets you into 320x200x256 mode. }
BEGIN
  asm
     mov        ax,0013h
     int        10h
  end;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure SetText;  { This procedure returns you to text mode.  }
BEGIN
  asm
     mov        ax,0003h
     int        10h
  end;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
procedure WaitRetrace; assembler;
  { This waits until you are in a Verticle Retrace ... this means that all
    screen manipulation you do only appears on screen in the next verticle
    retrace ... this removes most of the "fuzz" that you see on the screen
    when changing the pallette. It unfortunately slows down your program
    by "synching" your program with your monitor card ... it does mean
    that the program will run at almost the same speed on different
    speeds of computers which have similar monitors. In our SilkyDemo,
    we used a WaitRetrace, and it therefore runs at the same (fairly
    fast) speed when Turbo is on or off. }
 
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;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure GetPal(ColorNo : Byte; Var R,G,B : Byte);
  { This reads the values of the Red, Green and Blue values of a certain
    color and returns them to you. }
Begin
   Port[$3c7] := ColorNo;
   R := Port[$3c9];
   G := Port[$3c9];
   B := Port[$3c9];
End;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure Pal(ColorNo : Byte; R,G,B : Byte);
  { This sets the Red, Green and Blue values of a certain color }
Begin
   Port[$3c8] := ColorNo;
   Port[$3c9] := R;
   Port[$3c9] := G;
   Port[$3c9] := B;
End;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure Putpixel (X,Y : Integer; Col : Byte);
  { This puts a pixel on the screen by writing directly to memory. }
BEGIN
  Mem [VGA:X+(Y*320)]:=Col;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure line(a,b,c,d,col:integer);
  { This draws a line from a,b to c,d of color 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 u,s,v,d1x,d1y,d2x,d2y,m,n:real;
    i: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 := INT(m / 2);
     FOR i := 0 TO round(m) DO
     BEGIN
          putpixel(a,b,col);
          s := s + n;
          IF not (s<m) THEN
          BEGIN
               s := s - m;
               a:= a +round(d1x);
               b := b + round(d1y);
          END
          ELSE
          BEGIN
               a := a + round(d2x);
               b := b + round(d2y);
          END;
     END;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure PalPlay;
  { This procedure mucks about with our "virtual pallette", then shoves it
    to screen. }
Var Tmp : Array[1..3] of Byte;
  { This is used as a "temporary color" in our pallette }
    loop1 : Integer;
BEGIN
   Move(Pall[200],Tmp,3);
     { This copies color 200 from our virtual pallette to the Tmp variable }
   Move(Pall[0],Pall[1],200*3);
     { This moves the entire virtual pallette up one color }
   Move(Tmp,Pall[0],3);
     { This copies the Tmp variable to the bottom of the virtual pallette }
   WaitRetrace;
   For loop1:=1 to 255 do
     pal (loop1,pall[loop1,1],pall[loop1,2],pall[loop1,3]);
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure SetUpScreen;
  { This gets our screen ready but setting up the pallette and drawing
    the lines. }
Var j,Loop : Integer;
BEGIN
   FillChar(Pall,SizeOf(Pall),0);
       { Clear the entire PALL variable to zero. }
   For Loop := 0 to 31 do BEGIN
      Pall[Loop,1] := (Loop mod 64) + 32; END;
   j := 63;
   For Loop := 32 to 63 do BEGIN
      Pall[Loop,1] := j; dec(j); END;
   For Loop := 64 to 127 do BEGIN
      Pall[Loop,2] := Loop mod 64; END;
   For Loop := 128 to 196 do BEGIN
      Pall[Loop,3] := Loop mod 64;
 
   END;
       { This sets colors 0 to 200 in the PALL variable to values between
         0 to 63. the MOD function gives you the remainder of a division,
         ie. 105 mod 10 = 5 }
 
   For Loop := 1 to 320 do BEGIN
      Line(320-Loop,199,320-Loop,0,(Loop Mod 201)+1);
       { These two lines start drawing lines from the left and the right
         hand sides of the screen, using colors 1 to 199. Look at these
         two lines and understand them. }
      PalPlay;
        { This calls the PalPlay procedure }
   END;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure GrabPallette;
VAR loop1:integer;
BEGIN
  For loop1:=0 to 255 do
    Getpal (loop1,pall2[loop1,1],pall2[loop1,2],pall2[loop1,3]);
END;
 
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure Blackout;
  { This procedure blackens the screen by setting the pallette values of
    all the colors to zero. }
VAR loop1:integer;
BEGIN
  WaitRetrace;
  For loop1:=0 to 255 do
    Pal (loop1,0,0,0);
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure HiddenScreenSetup;
  { This procedure sets up the screen while it is blacked out, so that the
    user can't see what is happening. }
VAR loop1,loop2:integer;
BEGIN
  For loop1:=0 to 319 do
    For loop2:=0 to 199 do
      PutPixel (loop1,loop2,Random (256));
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure Fadeup;
  { This procedure slowly fades up the new screen }
VAR loop1,loop2:integer;
    Tmp : Array [1..3] of byte;
      { This is temporary storage for the values of a color }
BEGIN
  For loop1:=1 to 64 do BEGIN
      { A color value for Red, green or blue is 0 to 63, so this loop only
        need be executed a maximum of 64 times }
    WaitRetrace;
    For loop2:=0 to 255 do BEGIN
      Getpal (loop2,Tmp[1],Tmp[2],Tmp[3]);
      If Tmp[1]<Pall2[loop2,1] then inc (Tmp[1]);
      If Tmp[2]<Pall2[loop2,2] then inc (Tmp[2]);
      If Tmp[3]<Pall2[loop2,3] then inc (Tmp[3]);
        { If the Red, Green or Blue values of color loop2 are less then they
          should be, increase them by one. }
      Pal (loop2,Tmp[1],Tmp[2],Tmp[3]);
        { Set the new, altered pallette color. }
    END;
  END;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure FadeDown;
  { This procedure fades the screen out to black. }
VAR loop1,loop2:integer;
    Tmp : Array [1..3] of byte;
      { This is temporary storage for the values of a color }
BEGIN
  For loop1:=1 to 64 do BEGIN
    WaitRetrace;
    For loop2:=0 to 255 do BEGIN
      Getpal (loop2,Tmp[1],Tmp[2],Tmp[3]);
      If Tmp[1]>0 then dec (Tmp[1]);
      If Tmp[2]>0 then dec (Tmp[2]);
      If Tmp[3]>0 then dec (Tmp[3]);
        { If the Red, Green or Blue values of color loop2 are not yet zero,
          then, decrease them by one. }
      Pal (loop2,Tmp[1],Tmp[2],Tmp[3]);
        { Set the new, altered pallette color. }
    END;
  END;
END;
 
 
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure RestorePallette;
  { This procedure restores the origional pallette }
VAR loop1:integer;
BEGIN
  WaitRetrace;
  For loop1:=0 to 255 do
    pal (loop1,Pall2[loop1,1],Pall2[loop1,2],Pall2[loop1,3]);
END;
 
 
BEGIN
  ClrScr;
  Writeln ('This program will draw lines of different colors across the');
  Writeln ('screen and change them only by changing their pallette values.');
  Writeln ('The nice thing about using the pallette is that one pallette');
  Writeln ('change changes the same color over the whole screen, without');
  Writeln ('you having to redraw it. Because I am using a WaitRetrace');
  Writeln ('command, turning on and off your turbo during the demonstration');
  Writeln ('should have no effect.');
  Writeln;
  Writeln ('The second part of the demo blacks out the screen using the');
  Writeln ('pallette, fades in the screen, waits for a keypress, then fades');
  Writeln ('it out again. I haven''t put in any delays for the fadein/out,');
  Writeln ('so you will have to put ''em in yourself to get it to the speed you');
  Writeln ('like. Have fun and enjoy! ;-)');
  Writeln; Writeln;
  Writeln ('Hit any key to continue ...');
  Readkey;
  SetMCGA;
  GrabPallette;
  SetUpScreen;
  repeat
     PalPlay;
       { Call the PalPlay procedure repeatedly until a key is pressed. }
  Until Keypressed;
  Readkey;
    { Read in the key pressed otherwise it is left in the keyboard buffer }
  Blackout;
  HiddenScreenSetup;
{  FadeUp;
  Readkey;
  FadeDown;
  Readkey;}
  RestorePallette;
  SetText;
  Writeln ('All done. This concludes the second sample program in the ASPHYXIA');
  Writeln ('Training series. You may reach DENTHOR under the name of GRANT');
  Writeln ('SMITH on the MailBox BBS, or leave a message to ASPHYXIA on the');
  Writeln ('ASPHYXIA BBS. Get the numbers from Roblist, or write to :');
  Writeln ('             Grant Smith');
  Writeln ('             P.O. Box 270');
  Writeln ('             Kloof');
  Writeln ('             3640');
  Writeln ('I hope to hear from you soon!');
  Writeln; Writeln;
  Write   ('Hit any key to exit ...');
  Readkey;
END.

/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// TUTPROG2.CPP - VGA Trainer Program 2 (in Turbo C++ 3.0)                 //
//                                                                         //
// "The VGA Trainer Program" is written by Denthor of Asphyxia. However it //
// was limited to Pascal only in its first run.  All I have done is taken  //
// his original release, translated it to C++ and touched up a few things. //
// I take absolutely no credit for the concepts presented in this code and //
// am NOT the person to ask for help if you are having trouble.            //
//                                                                         //
// Program Notes : This program presents many new concepts, including:     //
//                 line drawing, pallette manipulation, and fading.        //
//                                                                         //
//                 If you are compiling this code command line, be sure to //
//                 use the "-ml" parameter (large memory model).           //
//                 Otherwise, the program will compile and link, but will  //
//                 lock up your system.                                    //
//                                                                         //
// Author        : Grant Smith (Denthor) - denthor@beastie.cs.und.ac.za    //
// Translator    : Christopher G. Mann   - r3cgm@dax.cc.uakron.edu         //
//                                                                         //
// Last Modified : November 29, 1994                                       //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
 
//               //
// INCLUDE FILES //
//               //
 
  #include <conio.h>
			  // getch(), clrscr()
  #include <dos.h>
			  // MK_FP, Geninterrupt()
  #include <math.h>
			  // floor(), ceil()
  #include <mem.h>
			  // memset(), movmem()
  #include <iostream.h>
			  // cout
  #include <stdlib.h>
			  // abs(), rand()
 
 
//                     //
// FUNCTION PROTOTYPES //
//                     //
 
  // MODE SETTING FUNCTIONS
  void SetMCGA();
  void SetText();
 
  // PALLETTE FUNCTIONS
  void GrabPallette();
  void GetPal (unsigned char ColorNo,  unsigned char &R,
	       unsigned char &G,       unsigned char &B);
  void Pal    (unsigned char ColorNo,  unsigned char R,
	       unsigned char G,        unsigned char B);
  void PalPlay  ();
  void Fadeup   ();
  void FadeDown ();
  void Blackout ();
  void RestorePallette();
 
  // SMALL UTILITY FUNCTIONS
  int  sgn  (long a);
  int  round(long a);
 
  // DRAWING FUNCTIONS
  void Putpixel (int x, int y, unsigned char Col);
  void Line(int a, int b, int c, int d, int col);
  void WaitRetrace();
 
  // MID-LEVEL (COMBINATION) FUNCTIONS
  void SetUpScreen();
  void HiddenScreenSetup();
 
 
//                              //
// GLOBAL VARIABLE DECLARATIONS //
//                              //
 
  // declare a pointer to the offset of VGA memory
  unsigned char *vga = (unsigned char *) MK_FP(0xA000, 0);
 
  // This declares the PALL variable. 0 to 255 signifies the colors of the
  // pallette, 1 to 3 signifies the Red, Green and Blue values. I am
  // going to use this as a sort of "virtual pallette", and alter it
  // as much as I want, then suddenly bang it to screen. Pall2 is used
  // to "remember" the origional pallette so that we can restore it at
  // the end of the program. */
  unsigned char Pall[256][3], Pall2[256][3];
 
 
///////////////////////////////////////////////////////////////////////////////
//                                                                           //
//                                MAIN FUNCTION                              //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////
 
void main() {
 
  clrscr();
  cout << "This program will draw lines of different colors across the\n"
       << "screen and change them only by changing their pallette values.\n"
       << "The nice thing about using the pallette is that one pallette\n"
       << "change changes the same color over the whole screen, without\n"
       << "you having to redraw it. Because I am using a WaitRetrace\n"
       << "command, turning on and off your turbo during the demonstration\n"
       << "should have no effect." << endl << endl;
 
  cout << "The second part of the demo blacks out the screen using the\n"
       << "pallette, fades in the screen, waits for a keypress, then fades\n"
       << "it out again. I haven''t put in any delays for the fadein/out,\n"
       << "so you will have to put them in yourself to get to the speed\n"
       << "you like. Have fun and enjoy! ;-)" << endl << endl << endl;
  cout << "Hit any key to continue ...";
  getch();
 
  SetMCGA();
  GrabPallette();
  SetUpScreen();
 
  while (!kbhit()) PalPlay();
    getch();  // once a key is pressed, be sure to clear the keyboard buffer
 
  Blackout();
  HiddenScreenSetup();
  Fadeup();
  getch();
  FadeDown();
  getch();
 
  RestorePallette();
  SetText();
  cout << "All done. This concludes the second sample program in the ASPHYXIA\n"
       << "Training series. You may reach DENTHOR under the name of GRANT\n"
       << "SMITH on the MailBox BBS, or leave a message to ASPHYXIA on the\n"
       << "ASPHYXIA BBS. Get the numbers from Roblist, or write to :\n"
       << "             Grant Smith\n"
       << "             P.O. Box 270\n"
       << "             Kloof\n"
       << "             3640\n"
       << "I hope to hear from you soon!" << endl << endl << endl;
 
  cout << "Hit any key to exit ...";
  getch();
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// SetMCGA() - This function gets you into 320x200x256 mode.               //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void SetMCGA() {
  _AX = 0x0013;
  geninterrupt (0x10);
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// SetText() - This function gets you into text mode.                      //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void SetText() {
  _AX = 0x0003;
  geninterrupt (0x10);
}
 
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// GrabPallette() - This function retrieves the current pallette.          //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void GrabPallette() {
 
  for(int loop1=0;loop1<256;loop1++)
    GetPal(loop1,Pall2[loop1][0],Pall2[loop1][1],Pall2[loop1][2]);
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// GetPal() - This reads the values of the Red, Green, and Blue values of  //
//            a certain color.  This function uses pass-by-reference.      //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void GetPal(unsigned char ColorNo, unsigned char &R,
	    unsigned char &G,      unsigned char &B) {
 
  outp (0x03C7,ColorNo); // here is the pallette color I want read
  R = inp (0x03C9);
  G = inp (0x03C9);
  B = inp (0x03C9);
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// Pal() - This sets the Red, Green, and Blue values of a certain color.   //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void Pal(unsigned char ColorNo, unsigned char R,
	 unsigned char G,       unsigned char B) {
 
  outp (0x03C8,ColorNo); // here is the pallette color I want to set
  outp (0x03C9,R);
  outp (0x03C9,G);
  outp (0x03C9,B);
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// PalPlay() - This function mucks about with our "virtual pallette", then //
//             shoves it to the screen.                                    //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void PalPlay() {
 
unsigned char Tmp[3];
 
  // This copies color 200 from our virtual pallette to the Tmp variable.
  _fmemmove(Tmp,Pall[200],3);
 
  // This moves the entire virtual pallette up one color.
  _fmemmove(Pall[2],Pall[1],199*3);
 
  // This copies the Tmp variable to the bottom of the virtual pallette.
  // Don't change 0: leave this always black to not change overscan color.
  _fmemmove(Pall[1],Tmp,3);
 
  WaitRetrace();
  for (int loop1=0;loop1<256;loop1++)
   Pal(loop1,Pall[loop1][0], Pall[loop1][1], Pall[loop1][2]);
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// Fadeup() - This function slowly fades up the new screen                 //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void Fadeup() {
 
//This is temporary storage for the values of a color
unsigned char Tmp[3];
 
  // A color value for Red, green or blue is 0 to 63, so this loop only
  // need be executed a maximum of 64 times.
  for(int loop1=0;loop1<64;loop1++) {
 
    WaitRetrace();
 
    for(int loop2=0; loop2<256; loop2++) {
      GetPal(loop2,Tmp[0],Tmp[1],Tmp[2]);
 
      // If the Red, Green or Blue values of color loop2 are less then they
      // should be, increase them by one.
      if ((Tmp[0] < Pall2[loop2][0]) && (Tmp[0] < 63)) Tmp[0]++;
      if ((Tmp[1] < Pall2[loop2][1]) && (Tmp[1] < 63)) Tmp[1]++;
      if ((Tmp[2] < Pall2[loop2][2]) && (Tmp[2] < 63)) Tmp[2]++;
 
      // Set the new, altered pallette color.
      Pal (loop2,Tmp[0],Tmp[1],Tmp[2]);
    }
  }
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// FadeDown() - This function fades the screen out to black.               //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void FadeDown() {
 
// This is temporary storage for the values of a color
unsigned char Tmp[3];
 
  for(int loop1=0; loop1<64; loop1++) {
 
    WaitRetrace();
 
    for(int loop2=0; loop2<256; loop2++) {
      GetPal(loop2,Tmp[0],Tmp[1],Tmp[2]);
 
      // If the Red, Green or Blue values of color loop2 are not yet zero,
      // then, decrease them by one.
      if (Tmp[0] > 0) Tmp[0]--;
      if (Tmp[1] > 0) Tmp[1]--;
      if (Tmp[2] > 0) Tmp[2]--;
 
      // Set the new, altered pallette color.
      Pal(loop2,Tmp[0],Tmp[1],Tmp[2]);
    }
  }
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// Blackout() - This function just clears the screen.                      //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void Blackout() {
 
  WaitRetrace();
  for (int loop1=0;loop1<256;loop1++)
    Pal (loop1,0,0,0);
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// RestorePallette() - This function restores the origional pallette.      //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void RestorePallette() {
 
  WaitRetrace();
  for(int loop1=0; loop1<255; loop1++)
    Pal(loop1,Pall2[loop1][0],Pall2[loop1][1],Pall2[loop1][2]);
 
}
 
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// sgn() - This function is used by Line() to determine the sign of a long //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
int sgn (long a) {
 
  if (a > 0) return +1;
  else if (a < 0) return -1;
  else return 0;
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// round() - This function is used by Line() to round a long to the        //
//           nearest integer.                                              //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
int round (long a) {
  if ( (a - (int)a) < 0.5) return floor(a);
    else return ceil(a);
}
 
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// Putpixel() - This puts a pixel on the screen by writing directly to     //
//              memory.                                                    //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void Putpixel (int x, int y, unsigned char Col) {
 
  memset(vga+(x+(y*320)),Col,1);
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// Line() - This draws a line from a,b to c,d of color col.                //
//          This function will be explained in more detail in tut3new.zip  //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void Line(int a, int b, int c, int d, int col) {
 
long u,s,v,d1x,d1y,d2x,d2y,m,n;
int  i;
 
  u   = c-a;      // x2-x1
  v   = d-b;      // y2-y1
  d1x = sgn(u);   // d1x is the sign of u (x2-x1) (VALUE -1,0,1)
  d1y = sgn(v);   // d1y is the sign of v (y2-y1) (VALUE -1,0,1)
  d2x = sgn(u);   // d2x is the sign of u (x2-x1) (VALUE -1,0,1)
  d2y = 0;
  m   = abs(u);   // m is the distance between x1 and x2
  n   = abs(v);   // n is the distance between y1 and y2
 
  if (m<=n) {     // if the x distance is greater than the y distance
    d2x = 0;
    d2y = sgn(v); // d2y is the sign of v (x2-x1) (VALUE -1,0,1)
    m   = abs(v); // m is the distance between y1 and y2
    n   = abs(u); // n is the distance between x1 and x2
  }
 
  s = (int)(m / 2); // s is the m distance (either x or y) divided by 2
 
  for (i=0;i<round(m);i++) { // repeat this loop until it
			     // is = to m (y or x distance)
    Putpixel(a,b,col);       // plot a pixel at the original x1, y1
    s += n;                  // add n (dis of x or y) to s (dis of x of y)
    if (s >= m) {            // if s is >= m (distance between y1 and y2)
      s -= m;
      a += d1x;
      b += d1y;
    }
    else {
      a += d2x;
      b += d2y;
    }
  }
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// WaitRetrace() - This waits until you are in a Verticle Retrace ...      //
// 		   this means that all screen manipulation you do only     //
//		   appears on screen in the next verticle retrace ... this //
//		   removes most of the "fuzz" that you see on the screen   //
//		   when changing the pallette. It unfortunately slows down //
//		   your program by "synching" your program with your       //
//		   monitor card ... it does mean that the program will run //
//		   at almost the same speed on different speeds of         //
//		   computers which have similar monitors.  In our          //
//		   SilkyDemo, we used a WaitRetrace, and it therefore      //
//		   runs at the same (fairly fast) speed when Turbo is on   //
//		   or off.                                                 //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void WaitRetrace() {
 
  _DX = 0x03DA;
 
  l1: asm {
	in  al,dx;
	and al,0x08;
	jnz l1;
      }
 
  l2: asm {
	in  al,dx;
	and al,0x08;
	jz  l2;
      }
}
 
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// SetUpScreen() - This gets our screen ready by setting up the pallette   //
//                 and drawing the lines.                                  //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void SetUpScreen() {
 
  // Clear the entire PALL variable to zero.
  _fmemset(Pall,0,sizeof(Pall));
 
  // This sets colors 0 to 200 in the PALL variable to values between
  // 0 to 63. the modulus function gives you the remainder of a division,
  // ie. 105 % 10 = 5.
  for (int loop = 0; loop < 201;loop++)
    Pall[loop][0] = loop % 64;
 
  for (loop = 0; loop < 321; loop++) {
 
    // These two lines start drawing lines from the left and the right
    // hand sides of the screen, using colors 1 to 199. Look at these
    // two lines and understand them.
    Line(319,199,320-loop,0,(loop % 199) + 1);
    Line(0,0,loop,199,(loop % 199) + 1);
 
    // This calls the PalPlay function.
    PalPlay();
  }
 
}
 
/////////////////////////////////////////////////////////////////////////////
//                                                                         //
// HiddenScreenSetup() - This function sets up the screen while it is      //
//                       blacked out, so that the user can't see what is   //
//                       happening.                                        //
//                                                                         //
/////////////////////////////////////////////////////////////////////////////
 
void HiddenScreenSetup() {
 
  for (int loop1=0; loop1<320; loop1++)
    for (int loop2=0; loop2<200; loop2++)
      Putpixel (loop1,loop2, rand());
 
}