Mode 13h
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 1 ]==--
þ Introduction
Hi there! This is Denthor of ASPHYXIA, AKA Grant Smith. This training
program is aimed at all those budding young demo coders out there. I am
assuming that the reader is fairly young, has a bit of basic Std. 6 math
under his belt, has done a bit of programming before, probably in BASIC,
and wants to learn how to write a demo all of his/her own.
This I what I am going to do. I am going to describe how certain routines
work, and even give you working source code on how you do it. The source
code will assume that you have a VGA card that can handle the
320x200x256 mode. I will also assume that you have Turbo Pascal 6.0 or
above (this is because some of the code will be in Assembly language,
and Turbo Pascal 6.0 makes this incredibly easy to use). By the end of
the first "run" of sections, you will be able to code some cool demo
stuff all by yourself. The info you need, I will provide to you, but it
will be you who decides on the most spectacular way to use it.
Why not download some of our demos and see what I'm trying to head you
towards.
I will be posting one part a week on the Mailbox BBS. I have the first
"run" of sections worked out, but if you want me to also do sections on
other areas of coding, leave a message to Grant Smith in private E-Mail,
or start a conversation here in this conference. I will do a bit of
moderating of a sort, and point out things that have been done wrong.
In this, the first part, I will show you how you are supposed to set up
your Pascal program, how to get into 320x200x256 graphics mode without a
BGI file, and various methods of putpixels and a clearscreen utility.
NOTE : I drop source code all through my explanations. You needn't try
to grab all of it from all over the place, at the end of each part I
add a little program that uses all the new routines that we have
learned. If you do not fully understand a section, leave me
private mail telling me what you don't understand or asking how I
got something etc, and I will try to make myself clearer. One
last thing : When you spot a mistake I have made in one of my
parts, leave me mail and I will correct it post-haste.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ Disclaimer
Hi again, sorry that I have to add this, but here goes. All source code
obtained from this series of instruction programs is used at your own
risk. Denthor and the ASPHYXIA demo team hold no responsibility for any
loss or damage suffered by anyone through the use of this code. Look
guys, the code I'm going to give you has been used by us before in
Demos, Applications etc, and we have never had any compliants of machine
damage, but if something does go wrong with your computer, don't blame
us. Sorry, but that's the way it is.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ The MCGA mode and how you get into it in Pascal without a BGI
Lets face it. BGI's are next to worthless for demo coding. It is
difficult to find something that is slower then the BGI units for doing
graphics. Another thing is, they wern't really meant for 256 color
screens anyhow. You have to obtain a specific external 256VGA BGI to get
into it in Pascal, and it just doesn't make the grade.
So the question remains, how do we get into MCGA 320x200x256 mode in
Pascal without a BGI? The answer is simple : Assembly language.
Obviously assembly language has loads of functions to handle the VGA
card, and this is just one of them. If you look in Norton Gides to
Assembly Language, it says this ...
____________________________________________________________________
INT 10h, 00h (0) Set Video Mode
Sets the video mode.
On entry: AH 00h
AL Video mode
Returns: None
Registers destroyed: AX, SP, BP, SI, DI
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
This is all well and good, but what does it mean? It means that if you
plug in the video mode into AL and call interrupt 10h, SHAZAM! you are
in the mode of your choice. Now, the MCGA video mode is mode 13h, and
here is how we do it in Pascal.
Procedure SetMCGA;
BEGIN
asm
mov ax,0013h
int 10h
end;
END;
There you have it! One call to that procedure, and BANG you are in
320x200x256 mode. We can't actually do anything in it yet, so to go back
to text mode, you make the video mode equal to 03h, as seen below :
Procedure SetText;
BEGIN
asm
mov ax,0003h
int 10h
end;
END;
BANG! We are back in text mode! Now, cry all your enquiring minds, what
use is this? We can get into the mode, but how do we actually SHOW
something on the screen? For that, you must move onto the next section
....
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ Clearing the screen to a specific color
Now that we are in MCGA mode, how do we clear the screen. The answer is
simple : you must just remember that the base adress of the screen is
$a000. From $a000, the next 64000 bytes are what is actually displayed on
the screen (Note : 320 * 200 = 64000). So to clear the screen, you just use
the fillchar command (a basic Pascal command) like so :
FillChar (Mem [$a000:0],64000,Col);
What the mem command passes the Segment base and the Offset of a part of
memory : in this case the screen base is the Segment, and we are starting
at the top of the screen; Offset 0. The 64000 is the size of the screen
(see above), and Col is a value between 0 and 255, which represents the
color you want to clear the screen to.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
þ Putting a pixel on the screen (two different methoods)
If you look in Norton Guides about putting a pixel onto the screen, you
will see this :
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
Writes a pixel dot of a specified color at a specified screen
coordinate.
On entry: AH 0Ch
AL Pixel color
CX Horizontal position of pixel
DX Vertical position of pixel
BH Display page number (graphics modes with more
than 1 page)
Returns: None
Registers destroyed: AX, SP, BP, SI, DI
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
As seen from our SetMCGA example, you would write this by doing the following:
Procedure INTPutpixel (X,Y : Integer; Col : Byte);
BEGIN
asm
mov ah,0Ch
mov al,[col]
mov cx,[x]
mov dx,[y]
mov bx,[1]
int 10h
end;
END;
The X would be the X-Coordinate, the Y would be the Y-Coordinate, and the Col
would be the color of the pixel to place. Note that MCGA has 256 colors,
numbered 0 to 255. The startoff pallette is pretty grotty, and I will show
you how to alter it in my next lesson, but for now you will have to hunt for
colors that fit in for what you want to do. Luckily, a byte is 0 to 255, so
that is what we pass to the col variable. Have a look at the following.
CGA = 4 colours.
4x4 = 16
EGA = 16 colors.
16x16 = 256
VGA = 256 colors.
Therefore an EGA is a CGA squared, and a VGA is an EGA squared ;-)
Anyway, back to reality. Even though the abouve procedure is written in
assembly language, it is slooow. Why? I hear your enquiring minds cry. The
reason is simple : It uses interrupts (It calls INT 10h). Interrupts are
sloooow ... which is okay for getting into MCGA mode, but not for trying
to put down a pixel lickety-split. So, why not try the following ...
Procedure MEMPutpixel (X,Y : Integer; Col : Byte);
BEGIN
Mem [VGA:X+(Y*320)]:=Col;
END;
The Mem command, as we have seen above, allows you to point at a certain
point in memory ... the starting point is $a000, the base of the VGA's
memory, and then we specify how far into this base memory we start.
Think of the monitor this way. It starts in the top left hand corner at
0. As you increase the number, you start to move across the screen to your
right, until you reach 320. At 320, you have gone all the way across the
screen and come back out the left side, one pixel down. This carries on
until you reach 63999, at the bottom right hand side of the screen. This
is how we get the equation X+(Y*320). For every increased Y, we must
increment the number by 320. Once we are at the beginning of the Y line
we want, we add our X by how far out we want to be. This gives us the
exact point in memory that we want to be at, and then we set it equal to
the pixel value we want.
The MEM methood of putpixel is much faster, and it is shown in the sample
program at the end of this lesson. The ASPHYXIA team uses neither putpixel;
we use a DMA-Straight-To-Screen-Kill-Yer-Momma-With-An-Axe type putipixel
which is FAST. We will give it out, but only to those of you who show us
you are serious about coding. If you do do anything, upload it to me,
I will be very interested to see it. Remember : If you do glean anything
from these training sessions, give us a mention in your demos and UPLOAD
YOUR DEMO TO US!
Well, after this is the sample program; have fun with it, UNDERSTAND it,
and next week I will start on fun with the pallette.
See you all later,
- Denthor
{$X+} (* This is a handy little trick to know. If you put this at the top
of your program, you do not have to set a variable when calling
a function, i.e. you may just say 'READKEY' instead of
'CH:=READKEY' *)
USES Crt; (* This has a few nice functions in it, such as the
READKEY command. *)
CONST VGA = $a000; (* This sets the constant VGA to the segment of the
VGA screen. *)
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure SetMCGA; { This procedure gets you into 320x200x256 mode. }
BEGIN
asm
mov ax,0013h
int 10h
end;
END;
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure SetText; { This procedure returns you to text mode. }
BEGIN
asm
mov ax,0003h
int 10h
end;
END;
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure Cls (Col : Byte);
{ This clears the screen to the specified color }
BEGIN
Fillchar (Mem [$a000:0],64000,col);
END;
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure INTPutpixel (X,Y : Integer; Col : Byte);
{ This puts a pixel on the screen using interrupts. }
BEGIN
asm
mov ah,0Ch
mov al,[col]
mov cx,[x]
mov dx,[y]
mov bx,[1]
int 10h
end;
END;
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure TestINTPutpixel;
{ This tests out the speed of the INTPutpixel procedure. }
VAR loop1,loop2 : Integer;
BEGIN
For loop1:=0 to 319 do
For loop2:=0 to 199 do
INTPutpixel (loop1,loop2,Random (256));
Readkey;
Cls (0);
END;
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
Procedure MEMPutpixel (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 TestMEMPutpixel;
{ This tests out the speed of the MEMPutpixel procedure. }
VAR loop1,loop2 : Integer;
BEGIN
For loop1:=0 to 319 do
For loop2:=0 to 199 do
MEMPutpixel (loop1,loop2,Random (256));
Readkey;
Cls (0);
END;
{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
BEGIN (* Of the main program *)
ClrScr; { This clears the text Screen (CRT unit) }
Writeln ('What will happen is that I will clear the screen twice. After');
Writeln ('each clear screen you will have to hit a key. I will then fill');
Writeln ('the screen twice with randomlly colored pixels using two different');
Writeln ('methoods, after each of which you will have to hit a key. I will');
Writeln ('then return you to text mode.');
Writeln; Writeln;
Write ('Hit any kay to continue ...');
Readkey;
SetMCGA;
CLS (32);
Readkey;
CLS (90);
Readkey;
TestINTPutpixel;
TestMEMPutpixel;
SetText;
Writeln ('All done. This concludes the first 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. (* Of the main program *)
[BACK] Back
Discuss this article in the forums
See Also: © 1999-2011 Gamedev.net. All rights reserved. Terms of Use Privacy Policy
|