VGA Trainer Program: part 2
Õ-------------------------------¸
| W E L C O M E |
| To the VGA Trainer Program | |
| By | |
| DENTHOR of ASPHYXIA | | |
Ô-------------------------------¾ | |
--------------------------------Ù |
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--==[ 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 questions 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 separate.
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. Because intensities 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?
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;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
TUTPROG2.PAS
{$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. }
{--------------------------------------------------------------------------}
Procedure SetMCGA; { This procedure gets you into 320x200x256 mode. }
BEGIN
asm
mov ax,0013h
int 10h
end;
END;
{--------------------------------------------------------------------------}
Procedure SetText; { This procedure returns you to text mode. }
BEGIN
asm
mov ax,0003h
int 10h
end;
END;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
Procedure GrabPallette;
VAR loop1:integer;
BEGIN
For loop1:=0 to 255 do
Getpal (loop1,pall2[loop1,1],pall2[loop1,2],pall2[loop1,3]);
END;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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.
