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Turbo Pascal Graphics?

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Marcel Siegwart

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May 2, 1997, 3:00:00 AM5/2/97

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Hi everybody

I've been playing around with non-BGI pascal graphics based on
Asphyxia's graphichs tutorial(tutorial 1-9 included with this
message)and wrote a great program(I don't want to give it out - sorry),
but know I've been having some problems:

1. I am only able to work in 320x200 how do I switch to other
resolutions like the 101h graphics mode(please no BGI).

2. I have been having trouble accessing Asphyxia's page - is it down?

3. The routines givin in Asphyxia's tutorial are good, but are there
faster ways of doing them(When you read the tutorial they give some
hints that they have better routines like their faster putpixel routine)

4. How do you tell if one routine is faster than the other?

5. How big is BMP's headers?

6. I am also looking for a tutorial on assembler or something to do with
registers which can used in Turbo Pascal 7.

7. The repeat
utill keypress
routine I want to use in future programs. How do I know what key the
person pressed. (Maybe something to do with the keyboard buffer? If it
isn't I would also like to learn how to use the keyb. buffer.)

If you are able to answer only one question out of this group I would be
very pleased.

Sorry I cannot recieve mail(I really mean it). So your answer would have
to be left on this newsgroup

Thank you
Roelf Pringle

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ł W E L C O M E ł
ł To the VGA Trainer Program ł ł
ł By ł ł
ł DENTHOR of ASPHYXIA ł ł ł
ÔÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍľ ł ł
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ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄŮ

--==[ PART 1 ]==--

ţ 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.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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
....

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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

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

ţ 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.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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;

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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;

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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?

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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;

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ 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

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--==[ PART 3 ]==--

ţ Introduction

Greetings! This is the third part of the VGA Trainer series! Sorry it
took so long to get out, but I had a running battle with the traffic
department for three days to get my car registered, and then the MailBox
went down. Ahh, well, life stinks. Anyway, today will do some things
vital to most programs : Lines and circles.

Watch out for next week's part : Virtual screens. The easy way to
eliminate flicker, "doubled sprites", and subjecting the user to watch
you building your screen. Almost every ASPHYXIA demo has used a virtual
screen (with the exception of the SilkyDemo), so this is one to watch out
for. I will also show you how to put all of these loose procedures into
units.

If you would like to contact me, or the team, there are many ways you
can do it : 1) Write a message to Grant Smith in private mail here on
the Mailbox BBS.
2) Write a message here in the Programming conference here
on the Mailbox (Preferred if you have a general
programming query or problem others would benefit from)
3) Write to ASPHYXIA on the ASPHYXIA BBS.
4) Write to Denthor, Eze or Livewire on Connectix.
5) Write to : Grant Smith
P.O.Box 270 Kloof
3640
6) Call me (Grant Smith) at 73 2129 (leave a message if you
call during varsity)

NB : If you are a representative of a company or BBS, and want ASPHYXIA
to do you a demo, leave mail to me; we can discuss it.
NNB : If you have done/attempted a demo, SEND IT TO ME! We are feeling
quite lonely and want to meet/help out/exchange code with other demo
groups. What do you have to lose? Leave a message here and we can work
out how to transfer it. We really want to hear from you!

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Circle Algorithim

You all know what a circle looks like. But how do you draw one on the
computer?

You probably know circles drawn with the degrees at these points :

0
ÜŰ|ŰÜ
ŰŰŰ|ŰŰŰ
270 ----+---- 90
ŰŰŰ|ŰŰŰ
ßŰ|Űß
180

Sorry about my ASCI ;-) ... anyway, Pascal doesn't work that way ... it
works with radians instead of degrees. (You can convert radians to degrees,
but I'm not going to go into that now. Note though that in pascal, the
circle goes like this :

270
ÜŰ|ŰÜ
ŰŰŰ|ŰŰŰ
180 ----+---- 0
ŰŰŰ|ŰŰŰ
ßŰ|Űß
90

Even so, we can still use the famous equations to draw our circle ...
(You derive the following by using the theorem of our good friend
Pythagoras)
Sin (deg) = Y/R
Cos (deg) = X/R
(This is standard 8(?) maths ... if you haven't reached that level yet,
take this to your dad, or if you get stuck leave me a message and I'll
do a bit of basic Trig with you. I aim to please ;-))

Where Y = your Y-coord
X = your X-coord
R = your radius (the size of your circle)
deg = the degree

To simplify matters, we rewrite the equation to get our X and Y values :

Y = R*Sin(deg)
X = R*Cos(deg)

This obviousy is perfect for us, because it gives us our X and Y co-ords
to put into our putpixel routine (see Part 1). Because the Sin and Cos
functions return a Real value, we use a round function to transform it
into an Integer.

Procedure Circle (oX,oY,rad:integer;Col:Byte);
VAR deg:real;
X,Y:integer;
BEGIN
deg:=0;
repeat
X:=round(rad*COS (deg));
Y:=round(rad*sin (deg));
putpixel (x+ox,y+oy,Col);
deg:=deg+0.005;
until (deg>6.4);
END;

In the above example, the smaller the amount that deg is increased by,
the closer the pixels in the circle will be, but the slower the procedure.
0.005 seem to be best for the 320x200 screen. NOTE : ASPHYXIA does not use
this particular circle algorithm, ours is in assembly language, but this
one should be fast enough for most. If it isn't, give us the stuff you are
using it for and we'll give you ours.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Line algorithms

There are many ways to draw a line on the computer. I will describe one
and give you two. (The second one you can figure out for yourselves; it
is based on the first one but is faster)

The first thing you need to do is pass what you want the line to look
like to your line procedure. What I have done is said that x1,y1 is the
first point on the screen, and x2,y2 is the second point. We also pass the
color to the procedure. (Remember the screens top left hand corner is (0,0);
see Part 1)

Ie. o (X1,Y1)
ooooooooo
ooooooooo
oooooooo (X2,Y2)

Again, sorry about my drawings ;-)

To find the length of the line, we say the following :

XLength = ABS (x1-x2)
YLength = ABS (y1-y2)

The ABS function means that whatever the result, it will give you an
absolute, or posotive, answer. At this stage I set a variable stating
wheter the difference between the two x's are negative, zero or posotive.
(I do the same for the y's) If the difference is zero, I just use a loop
keeping the two with the zero difference posotive, then exit.

If neither the x's or y's have a zero difference, I calculate the X and Y
slopes, using the following two equations :

Xslope = Xlength / Ylength
Yslope = Ylength / Xlength

As you can see, the slopes are real numbers.
NOTE : XSlope = 1 / YSlope

Now, there are two ways of drawing the lines :

X = XSlope * Y
Y = YSlope * X

The question is, which one to use? if you use the wrong one, your line
will look like this :

o
o
o

Instead of this :

ooo
ooo
ooo

Well, the solution is as follows :

*\``|``/*
***\|/***
----+----
***/|\***
*/``|``\*

If the slope angle is in the area of the stars (*) then use the first
equation, if it is in the other section (`) then use the second one.
What you do is you calculate the variable on the left hand side by
putting the variable on the right hand side in a loop and solving. Below
is our finished line routine :

Procedure Line (x1,y1,x2,y2:integer;col:byte);
VAR x,y,xlength,ylength,dx,dy:integer;
xslope,yslope:real;
BEGIN
xlength:=abs (x1-x2);
if (x1-x2)<0 then dx:=-1;
if (x1-x2)=0 then dx:=0;
if (x1-x2)>0 then dx:=+1;
ylength:=abs (y1-y2);
if (y1-y2)<0 then dy:=-1;
if (y1-y2)=0 then dy:=0;
if (y1-y2)>0 then dy:=+1;
if (dy=0) then BEGIN
if dx<0 then for x:=x1 to x2 do
putpixel (x,y1,col);
if dx>0 then for x:=x2 to x1 do
putpixel (x,y1,col);
exit;
END;
if (dx=0) then BEGIN
if dy<0 then for y:=y1 to y2 do
putpixel (x1,y,col);
if dy>0 then for y:=y2 to y1 do
putpixel (x1,y,col);
exit;
END;
xslope:=xlength/ylength;
yslope:=ylength/xlength;
if (yslope/xslope<1) and (yslope/xslope>-1) then BEGIN
if dx<0 then for x:=x1 to x2 do BEGIN
y:= round (yslope*x);
putpixel (x,y,col);
END;
if dx>0 then for x:=x2 to x1 do BEGIN
y:= round (yslope*x);
putpixel (x,y,col);
END;
END
ELSE
BEGIN
if dy<0 then for y:=y1 to y2 do BEGIN
x:= round (xslope*y);
putpixel (x,y,col);
END;
if dy>0 then for y:=y2 to y1 do BEGIN
x:= round (xslope*y);
putpixel (x,y,col);
END;
END;
END;

Quite big, isn't it? Here is a much shorter way of doing much the same
thing :

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;

procedure line(a,b,c,d,col:integer);
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;

This routine is very fast, and should meet almost all of your requirements
(ASPHYXIA used it for quite a while before we made our new one.)
In the end program, both the new line routine and the circle routine are
tested. A few of the procedures of the first parts are also used.

Line and circle routines may seem like fairly trivial things, but they are
a vital component of many programs, and you may like to look up other
methods of drawing them in books in the library (I know that here at the
varsity they have books for doing this kind of stuff all over the place)
A good line routine to look out for is the Bressenhams line routine ...
there is a Bressenhams circle routine too ... I have documentaiton for them
if anybody is interested, they are by far some of the fastest routines
you will use.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ In closing

Varsity has started again, so I am (shock) going to bed before three in
the morning, so my quote this week wasn't written in the same wasted way
my last weeks one was (For last week's one, I had gotten 8 hours sleep in
3 days, and thought up and wrote the quote at 2:23 am before I fell asleep.)

[ "What does it do?" she asks.
"It's a computer," he replies.
"Yes, dear, but what does it do?"
"It ..er.. computes! It's a computer."
"What does it compute?"
"What? Er? Um. Numbers! Yes, numbers!" He smiles
worriedly.
"Why?"
"Why? Well ..um.. why?" He starts to sweat.
"I mean, is it just something to dust around, or does
it actually do something useful?"
"Um...you can call other computers with it!" Hope lights
up his eyes. "So you can get programs from other computers!"
"I see. Tell me, what do these programs do?"
"Do? I don't think I fol..."
"I see. They compute. Numbers. For no particular reason." He
withers under her gaze.
"Yes, but..."
She smiles, and he trails off, defeated. She takes another look
at the thing. "Although," she says, with a strange look in
her eyes. He looks up, an insane look of hope on his
face. "Does it come in pink?" she asks.
]
- Grant Smith
Tue 27 July, 1993
9:35 pm.

See you next time,
- Denthor

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--==[ PART 4 ]==--

ţ Introduction

Howdy all! Welcome to the fourth part of this trainer series! It's a
little late, but I am sure you will find that the wait was worth it,
becase today I am going to show you how to use a very powerful tool :
Virtual Screens.

NB : If you are a representative of a company or BBS, and want ASPHYXIA
to do you a demo, leave mail to me; we can discuss it.
NNB : If you have done/attempted a demo, SEND IT TO ME! We are feeling
quite lonely and want to meet/help out/exchange code with other demo
groups. What do you have to lose? Leave a message here and we can work
out how to transfer it. We really want to hear from you!

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ What is a Virtual Screen and why do we need it?

Let us say you are generating a complex screen numerous times on the fly
(for example scrolling up the screen then redrawing all the sprites for
each frame of a game you are writing.) Do you have any idea how awful it
would look if the user could actually see you erasing and redrawing each
sprite for each frame? Can you visualise the flicker effect this would
give off? Do you realise that there would be a "sprite doubling" effect
(where you see two copies of the same sprite next to each other)? In the
sample program I have included a part where I do not use virtual screens
to demonstrate these problems. Virtual screens are not the only way to
solve these problems, but they are definately the easiest to code in.

A virtual screen is this : a section of memory set aside that is exactly
like the VGA screen on which you do all your working, then "flip" it
on to your true screen. In EGA 640x350x16 you automatically have a
virtual page, and it is possible to have up to four on the MCGA using a
particular tweaked mode, but for our puposes we will set one up using base
memory.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Setting up a virtual screen

As you will have seen in the first part of this trainer series, the MCGA
screen is 64000 bytes big (320x200=64000). You may also have noticed that
in TP 6.0 you arn't allowed too much space for normal variables. For
example, saying :

VAR Virtual : Array [1..64000] of byte;

would be a no-no, as you wouldn't have any space for your other variables.
What is the solution? I hear you enquiring minds cry. The answer : pointers!
Pointers to not use up the base 64k allocated to you by TP 6.0, it gets
space from somewhere else in the base 640k memory of your computer. Here is
how you set them up :

Type Virtual = Array [1..64000] of byte; { The size of our Virtual Screen }
VirtPtr = ^Virtual; { Pointer to the virtual screen }

VAR Virscr : VirtPtr; { Our first Virtual screen }
Vaddr : word; { The segment of our virtual screen}

If you put this in a program as it stands, and try to acess VirScr, your
machine will probably crash. Why? Because you have to get the memory for
your pointers before you can acess them! You do that as follows :

Procedure SetUpVirtual;
BEGIN
GetMem (VirScr,64000);
vaddr := seg (virscr^);
END;

This procedure has got the memory for the screen, then set vaddr to the
screens segment. DON'T EVER LEAVE THIS PROCEDURE OUT OF YOUR PROGRAM!
If you leave it out, when you write to your virtual screen you will probably
be writing over DOS or some such thing. Not a good plan ;-).

When you have finished your program, you will want to free the memory
taken up by the virtual screen by doing the following :

Procedure ShutDown;
BEGIN
FreeMem (VirScr,64000);
END;

If you don't do this your other programs will have less memory to use for
themselves.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Putting a pixel to your virtual screen

This is very similar to putting a pixel to your normal MCGA screen, as
discussed in part one... here is our origonal putpixel :

Procedure PutPixel (X,Y : Integer; Col : Byte);
BEGIN
Mem [VGA:X+(Y*320)]:=col;
END;

For our virtual screen, we do the following :

Procedure VirtPutPixel (X,Y : Integer; Col : Byte);
BEGIN
Mem [Vaddr:X+(Y*320)]:=col;
END;

It seems quite wasteful to have two procedures doing exactly the same thing,
just to different screens, doesn't it? So why don't we combine the two like
this :

Procedure PutPixel (X,Y : Integer; Col : Byte; Where : Word);
BEGIN
Mem [Where:X+(Y*320)]:=col;
END;

To use this, you will say something like :

Putpixel (20,20,32,VGA);
PutPixel (30,30,64,Vaddr);

These two statements draw two pixels ... one to the VGA screen and one to
the virtual screen! Doesn't that make you jump with joy! ;-) You will
have noticed that we still can't actually SEE the virtual screen, so on to
the next part ...

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ How to "Flip" your virtual screen on to the true screen

You in fact already have to tools to do this yourselves from information
in the previous parts of this trainer series. We will of course use the
Move command, like so :

Move (Virscr^,mem [VGA:0],64000);

simple, eh? Yuo may want to wait for a verticle retrace (Part 2) before you
do that, as it may make the flip much smoother (and, alas, slower).

Note that most of our other procedures may be altered to support the
virtual screen, such as Cls etc. (see Part 1 of this series), using the
methoods described above (I have altered the CLS procedure in the sample
program given at the end of this Part.)

We of ASPHYXIA have used virtual screens in almost all of our demos.
Can you imagine how awful the SoftelDemo would have looked if you had to
watch us redrawing the moving background, text and vectorballs for EACH
FRAME? The flicker, doubling effects etc would have made it awful! So
we used a virtual screen, and are very pleased with the result.
Note, though, that to get the speed we needed to get the demo fast enough,
we wrote our sprites routines, flip routines, pallette routines etc. all
in assembly. The move command is very fast, but not as fast as ASM ;-)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ In closing

I am writing this on the varsity computers in between lectures. I prefer
writing & coding between 6pm and 4am, but it isn't a good plan when
varsity is on ;-), so this is the first part of the trainer series ever
written before 9pm.

I have been asked to do a part on scrolling the screen, so that is
probably what I will do for next week. Also, ASPHYXIA will soon be putting
up a small demo with source on the local boards. It will use routines
that we have discussed in this series, and demonstrate how powerful these
routines can be if used in the correct manner.

Some projects for you to do :
1) Rewrite the flip statement so that you can say :
flip (Vaddr,VGA);
flip (VGA,Vaddr);
( This is how ASPHYXIAS one works )

2) Put most of the routines (putpixel, cls, pal etc.) into a unit,
so that you do not need to duplicate the procedures in each program
you write. If you need help, leave me mail.

See you next week
- Denthor

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--==[ PART 5 ]==--

ţ Introduction

Hello! This is Denthor here with the 5 part of the ASPHYXIA VGA Trainer
Series : The Scrolling Saga. I have had many requests for information on
scrolling, so I decided to make it this weeks topic. Note that I do make
reference to my recently released program TEXTER5, which should be available
from wherever you get this message. (Note to Sysops : If you put the trainer
series up on your boards, please add WORMIE.ZIP and TEXTER5.ZIP as they
both suppliment this series)

By the way, sorry for the delay in the appearance of this part. Tests,
projects and a few wild days of sin at the Wild Coast all conspired
against the prompt appearance of this part. Also note I need more input as
to what I should do future parts on, so leave me mail.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ What is scrolling?

If you have ever seen a demo, you have probably seen some form of scrolling.
Our SILKYDEMO has quite a nice example of scrolling. What it is is a long
row of text moving across your screen, usually from right to left, eg :

H : Step 1
He : Step 2
Hel : Step 3
Hell : Step 4
Hello : Step 5
Hello : Step 6

etc. etc. See the program attatched for an example of scrolling.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ What do we scroll?

Usually, letters. Most groups put greetings and information in their
'scrollies', as they are termed. You can also scroll and entire screen
using the scrolling technique. Scrolling your text is a hell of a lot
less boring then just having it appear on your screen. Unfortunately,
'scrollies' have been used so many times in demos they are wearing a
bit thin, so usually they are accompanied by a cool picture or some nice
routine happening at the same time (In our SILKYDEMO we had a moving
checkerboard and colour bars going at the same time).

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ How do we scroll from side to side?

The theory behind scrolling is quite easy. Let us imagine that we are
scrolling a 16x16 font grabbed by TEXTER (;-)) across the top of the
screen (ie. 320 pixels) As we know, the VGA screen starts at zero at the
top left hand part of the screen, then counts up to the right to 319, then
goes back to the left hand side one pixel down at 320. (See Tut 1) This means
that a 16*320 scroller takes up the space 0 to 5119 on the screen. In ascii
this looks like this :

(0) . . (319)
(320) . . (639)
" " "
(4800) . . (5119)

Simple enough. Now what we do is we put down the first Y-line of the first
character onto the very right hand side of the screen , like so :

For loop1:=1 to 16 do
Putpixel (319,loop1-1,font['A',1,loop1],vga);

This will draw some stuff on the very right hand side. Your screen should now
look like this :

(0) . X. (319)
(320) . X. (639)
" " "
(4800) . X. (5119)

Next, we move each line one to the left, ie :

For loop1:=0 to 15 do
Move (mem[VGA:loop1*320+1],mem[VGA:loop1*320],320);

This scrolls the screen from right to left, which is the easiest to read.
To scroll the screen from left to right, swap the +1 onto the other side
of the command. Also, to increase the size of the portion scrolled, increase
the 15 to however many lines from the top you wish to scroll-1.

After this move, your screen will look like this :

(0) . X . (319)
(320) . X . (639)
" " "
(4800) . X . (5119)
^
Note this space

What you then do is draw in the next line on the right hand side, move it,
draw the next line, move it etc. etc. Tah-Dah! You have a scrolly! Fairly
simple, isn't it?

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ How do we scroll up or down?

To scroll up or down is also fairly simple. This can be used for 'movie
credit' endings (I once wrote a little game with a desert scrolling down
with you being a little robot on the bottom of the screen). The theory is
this : Draw the top line (or bottom line) then move the entire screen :

Move (mem[vga:0],mem[vga:320],63680);
{ 64000 - 320 = 63680 }

For scrolling down, or :

Move (mem[vga:320],mem[vga:0],63680);

For scrolling up. You then draw the next line and repeat.

Because of the simplicity of coding in a scrolly, most demos have one. It
is usually best to have something extra happening on the screen so that
the viewer doesn't get too bored, even, as I say, if it is only a really nice
picture.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ In closing

The University of Natal, Durban, Science Dept., now has 10 new 486's!
This is a great boon, as now I can program nice routines during frees
(even though I am a Commerce Student (Shhhhh) ;-) ). I can now use those
previously wasted hours that I spent socialising and making friends
coding instead ;-)

I suggest you get a copy of TEXTER, for coding demos with fonts, or in fact
almost any graphics application, it is an amazing help, and we have used it
for *ALL* our demos. (P.S. We have written many demos, but many have been
written for companies and have not been released for the general public)
NOTE : For TEXTER's test program TEST.PAS, add {$X+} {$R-} if you have range
checking on (I code with it off.)

[ "I'm from the Computer Inspection Agency, sir,
I'm here to check your computer. Here is
my identification."
"Certainly. Have a look, I'm clean. I don't have
any pirated software."
The C-man pushes past him and sits in front of the
computer. He notes the fact that the computer
is currently off with a look of disdain. He
makes a note on his clipboard. He boots up.
"What is this?" he asks, pointing at the screen.
"It's MasterMenu" stutters the man. "I wrote it
myself!"
"Do you know what the penalty is for using junk
like this on a private machine?" The C-man smiles.
"This is a two-month sentance in itself!"
"I'm sorry sir! It won't happen again!"
"I know. I'll make sure of that." He smiles again.
The C-man runs through the hard drive, checking for
illeagal software, bad programs and anti-government
propaganda. He notes with satisfaction that he has
enough to put this weenie away for ten years, not that
it mattered. He usually could just make something up.
He comes to the last entry on the aphebetised menu tree.
His hands jerk away from the keyboard. Then, tentatively,
he types in the three letters of doom. He looks at the
man, who is backing away with wide eyes and his hands
outstretched in front of him, as if to ward off a blow.
The C-man smiles, his lips a thin, hard line.
"Windows!"
]
- Grant Smith
1:55pm
16/9/93

Cheers,
- Denthor

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--==[ PART 6 ]==--

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Introduction

Hi there! I'm back, with the latest part in the series : Pregenerated
arrays. This is a fairly simple concept that can treble the speed of
your code, so have a look.

I still suggest that if you haven't got a copy of TEXTER that you get it.
This is shareware, written by me, that allows you to grab fonts and use
them in your own programs.

I downloaded the Friendly City BBS Demo, an intro for a PE BBS, written
by a new group called DamnRite, with coder Brett Step. The music was
excellent, written by Kon Wilms (If I'm not mistaken, he is an Amiga
weenie ;-)). A very nice first production, and I can't wait to see more
of their work. I will try con a local BBS to allow me to send Brett some
fido-mail.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Why do I need a lookup table? What is it?

A lookup table is an imaginary table in memory where you look up the
answers to certain mathematical equations instead of recalculating them
each time. This may speed things up considerably. Please note that a
lookup table is sometimes referred to as a pregenerated array.

One way of looking at a lookup table is as follows : Let us say that for
some obscure reason you need to calculate a lot of multiplications (eg.
5*5 , 7*4 , 9*2 etc.). Instead of actually doing a slow multiply each
time, you can generate a kind of bonds table, as seen below :

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ş 9 ş 9 ł 18 ł 27 ł 36 ł 45 ł 54 ł 63 ł 72 ł 81 ł
ČÍÍÍĘÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄŮ

This means that instead of calculating 9*4, you just find the 9 on the
top and the 4 on the side, and the resulting number is the answer. This
type of table is very useful when the equations are very long to do.

The example I am going to use for this part is that of circles. Cast
your minds back to Part 3 on lines and circles. The circle section took
quite a while to finish drawing, mainly because I had to calculate the
SIN and COS for EVERY SINGLE POINT. Calculating SIN and COS is obviously
very slow, and that was reflected in the speed of the section.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ How do I generate a lookup table?

This is very simple. In my example, I am drawing a circle. A circle has
360 degrees, but for greater accuracy, to draw my circle I will start
with zero and increase my degrees by 0.4. This means that in each circle
there need to be 8000 SINs and COSes (360/0.4=8000). Putting these into
the base 64k that Pascal allocates for normal variables is obviously not
a happening thing, so we define them as pointers in the following
manner:
TYPE table = Array [1..8000] of real;

VAR sintbl : ^table;
costbl : ^table;

Then in the program we get the memory for these two pointers. Asphyxia
was originally thinking of calling itself Creative Reboot Inc., mainly
because we always forgot to get the necessary memory for our pointers.
(Though a bit of creative assembly coding also contributed to this. We
wound up rating our reboots on a scale of 1 to 10 ;-)). The next obvious
step is to place our necessary answers into our lookup tables. This can
take a bit of time, so in a demo, you would do it in the very beginning
(people just think it's slow disk access or something), or after you
have shown a picture (while the viewer is admiring it, you are
calculating pi to its 37th degree in the background ;-)) Another way of
doing it is, after calculating it once, you save it to a file which you
then load into the variable at the beginning of the program. Anyway,
this is how we will calculate the table for our circle :

Procedure Setup;
VAR deg:real;
BEGIN
deg:=0;
for loop1:=1 to 8000 do BEGIN
deg:=deg+0.4;
costbl^[loop1]:=cos (rad(deg));
sintbl^[loop1]:=sin (rad(deg));
END;
END;

This will calculate the needed 16000 reals and place them into our two
variables. The amount of time this takes is dependant on your computer.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ How do I use a lookup table?

This is very easy. In your program, wherever you put
cos (rad(deg)),
you just replace it with :
costbl^[deg]

Easy, no? Note that the new "deg" variable is now an integer, always
between 1 and 8000.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Where else do I use lookup tables?

Lookup tables may be used in many different ways. For example, when
working out 3-dimensional objects, sin and cos are needed often, and are
best put in a lookup table. In a game, you may pregen the course an
enemy may take when attacking. Even saving a picture (for example, a
plasma screen) after generating it, then loading it up later is a form
of pregeneration.

When you feel that your program is going much too slow, your problems
may be totally sorted out by using a table. Or, maybe not. ;-)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ In closing

As you have seen above, lookup tables aren't all that exciting, but they
are useful and you need to know how to use them. The attached sample
program will demonstrate just how big a difference they can make.

Keep on coding, and if you finish anything, let me know about it! I
never get any mail, so all mail is greatly appreciated ;-)

Sorry, no quote today, it's hot and I'm tired. Maybe next time ;-)

- Denthor

--------------51E51D9163C8
Content-Type: text/plain; charset=iso-8859-1; name="Tut7.txt"
Content-Transfer-Encoding: 8bit
Content-Disposition: inline; filename="Tut7.txt"

--==[ PART 7 ]==--

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Introduction

Hello! By popular request, this part is all about animation. I will be
going over three methods of doing animation on a PC, and will
concerntrate specifically on one, which will be demonstrated in the
attached sample code.

Although not often used in demo coding, animation is usually used in
games coding, which can be almost as rewarding ;-)

In this part I will also be a lot less stingy with assembler code :)
Included will be a fairly fast pure assembler putpixel, an asm screen
flip command, an asm icon placer, an asm partial-flip and one or two
others. I will be explaining how these work in detail, so this may also
be used as a bit of an asm-trainer too.

By the way, I apologise for this part taking so long to be released, but
I only finished my exams a few days ago, and they of course took
preference ;-). I have also noticed that the MailBox BBS is no longer
operational, so the trainer will be uploaded regularly to the BBS lists
shown at the end of this tutorial.

If you would like to contact me, or the team, there are many ways you
can do it : 1) Write a message to Grant Smith/Denthor/Asphyxia in private mail
on the ASPHYXIA BBS.
2) Write a message in the Programming conference on the
For Your Eyes Only BBS (of which I am the Moderator )
This is preferred if you have a general programming query
or problem others would benefit from.
4) Write to Denthor, Eze or Livewire on Connectix.
5) Write to : Grant Smith
P.O.Box 270 Kloof
3640
Natal
6) Call me (Grant Smith) at (031) 73 2129 (leave a message if you
call during varsity)
7) Write to mcp...@beastie.cs.und.ac.za on InterNet, and
mention the word Denthor near the top of the letter.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ The Principals of Animation

I am sure all of you have seen a computer game with animation at one or
other time. There are a few things that an animation sequence must do in
order to give an impression of realism. Firstly, it must move,
preferably using different frames to add to the realism (for example,
with a man walking you should have different frames with the arms an
legs in different positions). Secondly, it must not destroy the
background, but restore it after it has passed over it.

This sounds obvious enough, but can be very difficult to code when you
have no idea of how to go about achieving that.

In this trainer I will discuss various methods of meeting these two
objectives.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Frames and Object Control

It is quite obvious that for most animation to succeed, you must have
numerous frames of the object in various poses (such as a man with
several frames of him walking). When shown one after the other, these
give the impression of natural movement.

So, how do we store these frames? I hear you cry. Well, the obvious
method is to store them in arrays. After drawing a frame in Autodesk
Animator and saving it as a .CEL, we usually use the following code to
load it in :

TYPE icon = Array [1..50,1..50] of byte;

VAR tree : icon;

Procedure LoadCEL (FileName : string; ScrPtr : pointer);
var
Fil : file;
Buf : array [1..1024] of byte;
BlocksRead, Count : word;
begin
assign (Fil, FileName);
reset (Fil, 1);
BlockRead (Fil, Buf, 800); { Read and ignore the 800 byte header }
Count := 0; BlocksRead := $FFFF;
while (not eof (Fil)) and (BlocksRead <> 0) do begin
BlockRead (Fil, mem [seg (ScrPtr^): ofs (ScrPtr^) + Count], 1024, BlocksRead);
Count := Count + 1024;
end;
close (Fil);
end;

BEGIN
Loadcel ('Tree.CEL',addr (tree));
END.

We now have the 50x50 picture of TREE.CEL in our array tree. We may access
this array in the usual manner (eg. col:=tree [25,30]). If the frame is
large, or if you have many frames, try using pointers (see previous
parts)

Now that we have the picture, how do we control the object? What if we
want multiple trees wandering around doing their own thing? The solution
is to have a record of information for each tree. A typical data
structure may look like the following :

TYPE Treeinfo = Record
x,y:word; { Where the tree is }
speed:byte; { How fast the tree is moving }
Direction:byte; { Where the tree is facing }
frame:byte { Which animation frame the tree is
currently involved in }
active:boolean; { Is the tree actually supposed to be
shown/used? }
END;

VAR Forest : Array [1..20] of Treeinfo;

You now have 20 trees, each with their own information, location etc.
These are accessed using the following means :
Forest [15].x:=100;
This would set the 15th tree's x coordinate to 100.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ Restoring the Overwritten Background

I will discuss three methods of doing this. These are NOT NECESSARILY
THE ONLY OR BEST WAYS TO DO THIS! You must experiment and decide which
is the best for your particular type of program.

METHOD 1 :

Step 1 : Create two virtual pages, Vaddr and Vaddr2.
Step 2 : Draw the background to Vaddr2.
Step 3 : Flip Vaddr2 to Vaddr.
Step 4 : Draw all the foreground objects onto Vaddr.
Step 5 : Flip Vaddr to VGA.
Step 6 : Repeat from 3 continuously.

In ascii, it looks like follows ...

+---------+ +---------+ +---------+
| | | | | |
| VGA | <======= | VADDR | <====== | VADDR2 |
| | | (bckgnd)| | (bckgnd)|
| | |+(icons) | | |
+---------+ +---------+ +---------+

The advantages of this approach is that it is straightforward, continual
reading of the background is not needed, there is no flicker and it is
simple to implement. The disadvantages are that two 64000 byte virtual
screens are needed, and the procedure is not very fast because of the
slow speed of flipping.

METHOD 2 :

Step 1 : Draw background to VGA.
Step 2 : Grab portion of background that icon will be placed on.
Step 3 : Place icon.
Step 4 : Replace portion of background from Step 2 over icon.
Step 5 : Repeat from step 2 continuously.

In terms of ascii ...

+---------+
| +--|------- + Background restored (3)
| * -|------> * Background saved to memory (1)
| ^ |
| +--|------- # Icon placed (2)
+---------+

The advantages of this method is that very little extra memory is
needed. The disadvantages are that writing to VGA is slower then writing
to memory, and there may be large amounts of flicker.

METHOD 3 :

Step 1 : Set up one virtual screen, VADDR.
Step 2 : Draw background to VADDR.
Step 3 : Flip VADDR to VGA.
Step 4 : Draw icon to VGA.
Step 5 : Transfer background portion from VADDR to VGA.
Step 6 : Repeat from step 4 continuously.

In ascii ...

+---------+ +---------+
| | | |
| VGA | | VADDR |
| | | (bckgnd)|
| Icon>* <|-----------|--+ |
+---------+ +---------+

The advantages are that writing from the virtual screen is quicker then
from VGA, and there is less flicker then in Method 2. Disadvantages are
that you are using a 64000 byte virtual screen, and flickering occurs
with large numbers of objects.

In the attached sample program, a mixture of Method 3 and Method 1 is
used. It is faster then Method 1, and has no flicker, unlike Method 3.
What I do is I use VADDR2 for background, but only restore the
background that has been changed to VADDR, before flipping to VGA.

In the sample program, you will see that I restore the entire background
of each of the icons, and then place all the icons. This is because if I
replace the background then place the icon on each object individually,
if two objects are overlapping, one is partially overwritten.

The following sections are explanations of how the various assembler
routines work. This will probably be fairly boring for you if you
already know assembler, but should help beginners and dabblers alike.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ The ASM Putpixel

To begin with, I will explain a few of the ASM variables and functions :

There are 4 register variables : AX,BX,CX,DX. These are words (double
bytes) with a range from 0 to 65535. You may access the high and low
bytes of these by replacing the X with a "H" for high or "L" for low.
For example, AL has a range from 0-255.

You also have two pointers : ES:DI and DS:SI. The part on the left is
the segment to which you are pointing (eg $a000), and the right hand
part is the offset, which is how far into the segment you are pointing.
Turbo Pascal places a variable over 16k into the base of a segment, ie.
DI or SI will be zero at the start of the variable.

If you wish to be pointing to pixel number 3000 on the VGA screen (see
previous parts for the layout of the VGA screen), ES would be equal to
$a000 and DI would be equal to 3000. You can quite as easily make ES or
DS be equal to the offset of a virtual screen.

Here are a few functions that you will need to know :

mov destination,source This moves the value in source to
destination. eg mov ax,50
add destination,source This adds source to destination,
the result being stored in destination
mul source This multiplies AX by source. If
source is a byte, the source is
multiplied by AL, the result being
stored in AX. If source is a word,
the source is multiplied by AX, the
result being stored in DX:AX
movsb This moves the byte that DS:SI is
pointing to into ES:DI, and
increments SI and DI.
movsw Same as movsb except it moves a
word instead of a byte.
stosw This moves AX into ES:DI. stosb
moves AL into ES:DI. DI is then
incremented.
push register This saves the value of register by
pushing it onto the stack. The
register may then be altered, but
will be restored to it's original
value when popped.
pop register This restores the value of a pushed
register. NOTE : Pushed values must
be popped in the SAME ORDER but
REVERSED.
rep command This repeats Command by as many
times as the value in CX

SHL Destination,count ;
and SHR Destination,count ;
need a bit more explaining. As you know, computers think in ones and
zeroes. Each number may be represented in this base 2 operation. A byte
consists of 8 ones and zeroes (bits), and have a range from 0 to 255. A
word consists of 16 ones and zeroes (bits), and has a range from 0 to
65535. A double word consists of 32 bits.

The number 53 may be represented as follows : 00110101. Ask someone who
looks clever to explain to you how to convert from binary to decimal and
vice-versa.

What happens if you shift everything to the left? Drop the leftmost
number and add a zero to the right? This is what happens :

00110101 = 53
<-----
01101010 = 106

As you can see, the value has doubled! In the same way, by shifting one
to the right, you halve the value! This is a VERY quick way of
multiplying or dividing by 2. (note that for dividing by shifting, we
get the trunc of the result ... ie. 15 shr 1 = 7)

In assembler the format is SHL destination,count This shifts
destination by as many bits in count (1=*2, 2=*4, 3=*8, 4=*16 etc)
Note that a shift takes only 2 clock cycles, while a mul can take up to 133
clock cycles. Quite a difference, no? Only 286es or above may have count
being greater then one.

This is why to do the following to calculate the screen coordinates for
a putpixel is very slow :

mov ax,[Y]
mov bx,320
mul bx
add ax,[X]
mov di,ax

But alas! I hear you cry. 320 is not a value you may shift by, as you
may only shift by 2,4,8,16,32,64,128,256,512 etc.etc. The solution is
very cunning. Watch.

mov bx,[X]
mov dx,[Y]
push bx
mov bx, dx {; bx = dx = Y}
mov dh, dl {; dh = dl = Y}
xor dl, dl {; These 2 lines equal dx*256 }
shl bx, 1
shl bx, 1
shl bx, 1
shl bx, 1
shl bx, 1
shl bx, 1 {; bx = bx * 64}
add dx, bx {; dx = dx + bx (ie y*320)}
pop bx {; get back our x}
add bx, dx {; finalise location}
mov di, bx

Let us have a look at this a bit closer shall we?
bx=dx=y dx=dx*256 ; bx=bx*64 ( Note, 256+64 = 320 )

dx+bx=Correct y value, just add X!

As you can see, in assembler, the shortest code is often not the
fastest.

The complete putpixel procedure is as follows :

Procedure Putpixel (X,Y : Integer; Col : Byte; where:word);
{ This puts a pixel on the screen by writing directly to memory. }
BEGIN
Asm
push ds {; Make sure these two go out the }
push es {; same they went in }
mov ax,[where]
mov es,ax {; Point to segment of screen }
mov bx,[X]
mov dx,[Y]
push bx {; and this again for later}
mov bx, dx {; bx = dx}
mov dh, dl {; dx = dx * 256}
xor dl, dl
shl bx, 1
shl bx, 1
shl bx, 1
shl bx, 1
shl bx, 1
shl bx, 1 {; bx = bx * 64}
add dx, bx {; dx = dx + bx (ie y*320)}
pop bx {; get back our x}
add bx, dx {; finalise location}
mov di, bx {; di = offset }
{; es:di = where to go}
xor al,al
mov ah, [Col]
mov es:[di],ah {; move the value in ah to screen
point es:[di] }
pop es
pop ds
End;
END;

Note that with DI and SI, when you use them :
mov di,50 Moves di to position 50
mov [di],50 Moves 50 into the place di is pointing to

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ The Flip Procedure

This is fairly straightforward. We get ES:DI to point to the start of
the destination screen, and DS:SI to point to the start of the source
screen, then do 32000 movsw (64000 bytes).

procedure flip(source,dest:Word);
{ This copies the entire screen at "source" to destination }
begin
asm
push ds
mov ax, [Dest]
mov es, ax { ES = Segment of source }
mov ax, [Source]
mov ds, ax { DS = Segment of source }
xor si, si { SI = 0 Faster then mov si,0 }
xor di, di { DI = 0 }
mov cx, 32000
rep movsw { Repeat movsw 32000 times }
pop ds
end;
end;

The cls procedure works in much the same way, only it moves the color
into AX then uses a rep stosw (see program for details)

The PAL command is almost exactly the same as it's Pascal equivalent
(see previous tutorials). Look in the sample code to see how it uses the
out and in commands.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
ţ In Closing

The assembler procedures presented to you in here are not at their best.
Most of these are procedures ASPHYXIA abandoned for better ones after
months of use. But, as you will soon see, they are all MUCH faster then
the original Pascal equivalents I originally gave you. In future, I
hope to give you more and more assembler procedures for your ever
growing collections. But, as you know, I am not always very prompt with
this series (I don't know if even one has been released within one week
of the previous one), so if you want to get any stuff done, try do it
yourself. What do you have to lose, aside from your temper and a few
rather inventive reboots ;-)

What should I do for the next trainer? A simple 3-d tutorial? You may
not like it, because I would go into minute detail of how it works :)
Leave me suggestions for future trainers by any of the means discussed
at the top of this trainer.

After the customary quote, I will place a listing of the BBSes I
currently know that regularly carry this Trainer Series. If your BBS
receives it regularly, no matter where in the country you are, get a
message to me and I'll add it to the list. Let's make it more convenient
for locals to grab a copy without calling long distance ;-)

[ There they sit, the preschooler class encircling their
mentor, the substitute teacher.
"Now class, today we will talk about what you want to be
when you grow up. Isn't that fun?" The teacher looks
around and spots the child, silent, apart from the others
and deep in thought. "Jonny, why don't you start?" she
encourages him.
Jonny looks around, confused, his train of thought
disrupted. He collects himself, and stares at the teacher
with a steady eye. "I want to code demos," he says,
his words becoming stronger and more confidant as he

speaks. "I want to write something that will change
peoples perception of reality. I want them to walk
away from the computer dazed, unsure of their footing
and eyesight. I want to write something that will
reach out of the screen and grab them, making
heartbeats and breathing slow to almost a halt. I want
to write something that, when it is finished, they
are reluctant to leave, knowing that nothing they
experience that day will be quite as real, as
insightful, as good. I want to write demos."
Silence. The class and the teacher stare at Jonny, stunned. It
is the teachers turn to be confused. Jonny blushes,
feeling that something more is required. "Either that
or I want to be a fireman."
]
- Grant Smith
14:32
21/11/93

See you next time,
- DENTHOR

These fine BBS's carry the ASPHYXIA DEMO TRAINER SERIES : (alphabetical)

ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍËÍÍÍËÍÍÍÍËÍÍÍÍ»
şBBS Name şTelephone No. şOpen şMsgşFileşPastş
ĚÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÎÍÍÍÎÍÍÍÍÎÍÍÍÍą
şASPHYXIA BBS #1 ş(031) 765-5312 şALL ş * ş * ş * ş
şASPHYXIA BBS #2 ş(031) 765-6293 şALL ş * ş * ş * ş
şConnectix BBS ş(031) 266-9992 şALL ş * ş * ş * ş
şFor Your Eyes Only BBS ş(031) 285-318 şA/H ş * ş * ş * ş
ČÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍĘÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍĘÍÍÍÍÍĘÍÍÍĘÍÍÍÍĘÍÍÍÍĽ

Open = Open at all times or only A/H
Msg = Available in message base
File = Available in file base
Past = Previous Parts available

--------------51E51D9163C8--

david.c...@sunderland.ac.uk

unread,

May 2, 1997, 3:00:00 AM5/2/97

4)
One way of clocking the speed of a routine would be to put it in a
loop and repeat it say a million times. You could read the system
clock before and after the loop and work out the speed. This will not
be exactly right though unless you can disable system interrupts
during execution and include the time taken to perform the loops own
code but it will give you some idea of the speed.

I suppose that if you wanted to be more accurate you could
dissassemble the code for the routine into assembler and consult a
8086 manual to find out how many clock cycles each instruction takes.

6) Try the Turbo assembler manual, TASM code is mostly compatible with
assembler written using the asm statement in pascal I think.
But you could also try Using Assembly Language 2nd Ed published by QUE
(sorry don't know the author) which covers TASM and MASM. I haven't
read it myself but I have found that the one covering Turbo Pascal is
an excellent reference and provides loads of examples.

7) The readkey function in pascal can be used to find which key was
pressed. The turbo ide help files give this routine as an example.

uses Crt;

var
C: Char;

begin
Writeln('Please press a key');
C := Readkey;
Writeln(' You pressed ', C, ', whose ASCII value is ', Ord(C), '.');
end.

So you get a value for each key and then you can compare it to the
value you are looking for.

Actually I think each of the keys has a scan code that is stored in
one word of data. the high byte is the ASCII byte and the low one the
extended byte. If the character is one of the 256 ASCII characters
then it's code is stored in the ASCII byte and the extended is left as
0 or undefined.
Alternatively if the key is a "special" key eg PgUp the ascii byte is
0 and the extended byte is set (in this case to 73).

When you strike a key or keys the words are stored in the circular 32
byte keyboard buffer (located at $0040:$001E) and the characters are
read from there one word at a time.
The charaters are stored first come first served and overwrite the
previous contents in a sort of queue. The start of the queue is
pointed to by the head which is at $0040:$001A and the tail at
[$0040:$001C] points to the next open slot. The head and tail are not
part of the queue itself but the bytes in these positions have values
from $1E to $3C indicating the offsets they reference.The tail just
keeps incrementing until all 15 slots are filled and the buffer is
full. You get a beep from your pc if you try to enter more.
Once at the end of the buffer, the tail wraps around and is reset to
the lowest location.

If the head and tail point to the same place the buffer is empty.

You can access the data in the buffer using the MEM array. So for
example the line

if keypressed then ......

is equivalent to

if Mem[$0040:$001A] <> Mem[$0040:$001C] then ...

If you want to be sure that you are reading the correct keystrokes you
can flush the buffer using one of these routines

Procedure Fbuffer;
var MT:char;
begin
while keypressed do MT:=readkey;
end; {uses CRT rqd}

or just

procedure FBuffer;
begin
Mem[$0040:$001A] := Mem[$0040:$001C];
end; {head pointer := tailpointer}

Hope this Helps
Actually the trainer program looks pretty good and I would definitly
be interested in anything else like this if posted.

Dave

On Fri, 02 May 1997 12:30:00 +0200, Marcel Siegwart
<marcel.s...@sm-philnat.unibe.ch> wrote:

>This is a multi-part message in MIME format.
>
>--------------51E51D9163C8
>
>

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