VGA Trainer Program: part 1
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| W E L C O M E |
| To the VGA Trainer Program | |
| By | |
| DENTHOR of ASPHYXIA | | |
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--==[ PART 1 ]==--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.
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 complaints of machine damage, but if something does go wrong with your computer, don't blame us. Sorry, but that's the way it is.
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, DIThis 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 ....
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 address 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.
Putting a pixel on the screen (two different methods)
If you look in Norton Guides about putting a pixel onto the screen, you will see this :
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, DIAs 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 above 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 $a000, the base of the VGA's memory, and then we specify how far into this base memory we start. Think of the monitor this way. It starts in the top left hand corner at 0. As you increase the number, you start to move across the screen to your right, until you reach 320. At 320, you have gone all the way across the screen and come back out the left side, one pixel down. This carries on until you reach 63999, at the bottom right hand side of the screen. This is how we get the equation X+(Y*320). For every increased Y, we must increment the number by 320. Once we are at the beginning of the Y line we want, we add our X by how far out we want to be. This gives us the exact point in memory that we want to be at, and then we set it equal to the pixel value we want.
The MEM method of putpixel is much faster, and it is shown in the sample program at the end of this lesson. The ASPHYXIA team uses neither putpixel; we use a DMA-Straight-To-Screen-Kill-Yer-Momma-With-An-Axe type putipixel which is FAST. We will give it out, but only to those of you who show us you are serious about coding. If you do do anything, upload it to me, I will be very interested to see it. Remember : If you do glean anything from these training sessions, give us a mention in your demos and UPLOAD YOUR DEMO TO US!
Well, after this is the sample program; have fun with it, UNDERSTAND it, and next week I will start on fun with the pallette.
See you all later,
- Denthor
TUTPROG1.PAS
{$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 = $a000; (* This sets the constant VGA to the segment of the
VGA screen. *)
{--------------------------------------------------------------------------}
Procedure SetMCGA; { This procedure gets you into 320x200x256 mode. }
BEGIN
asm
mov ax,0013h
int 10h
end;
END;
{--------------------------------------------------------------------------}
Procedure SetText; { This procedure returns you to text mode. }
BEGIN
asm
mov ax,0003h
int 10h
end;
END;
{--------------------------------------------------------------------------}
Procedure Cls (Col : Byte);
{ This clears the screen to the specified color }
BEGIN
Fillchar (Mem [$a000:0],64000,col);
END;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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;
{--------------------------------------------------------------------------}
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 *)
