Pallette Changing

                    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 2 ]==--

  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.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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;

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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)

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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;

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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]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;

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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

 {$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. }

 {陳陳陳陳陳陳陳陳陳陳陳陳陳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 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳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(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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳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(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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳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);
   { This puts a pixel on the screen by writing directly to memory. }
 BEGIN
   Mem [VGA:X+(Y*320)]:=Col;
 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,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 (s0 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳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 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.

 [BACK] Back

Discuss this article in the forums


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

© 1999-2011 Gamedev.net. All rights reserved. Terms of Use Privacy Policy
Comments? Questions? Feedback? Click here!