ÕÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͸
                   ³         W E L C O M E         ³
                   ³  To the VGA Trainer Program   ³ ³
                   ³              By               ³ ³
                   ³      DENTHOR of ASPHYXIA      ³ ³ ³
                   ÔÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ; ³ ³
                     ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³
                       ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

                           --==[ PART 2 ]==--



þ Introduction



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.


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  What is the Pallette?

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 pallette. 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 pallette of either of them will they be able to
tell the difference. Also, by changing the whole pallette, you can obtain
the "Fade in" and "Fade out" effects found in many demos and games.
Pallette manipulation can become quite confusing to some people, because
colors that look the same are in fact totally seperate.


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  How do I read in the pallette value of a color?

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;

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  How do I set the pallette value of a color?

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)


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  How do I stop the "fuzz" that appears on my screen when I change the
        pallette?

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.

NOTE : WaitRetrace can be a great help to your coding ... code that fits
       into one retrace will mean that the demo will run at the same
       speed no matter what your computer speed (unless you are doing a lot
       during the WaitRetrace and the computer is slooooow). Note that in
       the following sample program and in our SilkyDemo, the thing will run
       at the same speed whether turbo is on or off.


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  How do I black out the screen using the pallette?

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 of
    all the colors to zero. }
VAR loop1:integer;
BEGIN
  WaitRetrace;
  For loop1:=0 to 255 do
    Pal (loop1,0,0,0);
END;


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  How do I fade in a screen?

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?


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ  How do I fade out a screen?

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;


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

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


ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
³ TUTPROG2.PAS ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

{$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 Loop : Integer;
BEGIN
   FillChar(Pall,SizeOf(Pall),0);
       { Clear the entire PALL variable to zero. }
   For Loop := 0 to 200 do BEGIN
      Pall[Loop,1] := 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(319,199,320-Loop,0,(Loop Mod 199)+1);
      Line(0,0,Loop,199,(Loop Mod 199)+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.