[Home]
[Edit this page]
[Recent Changes]
[Special Pages]
[Help]
DenTut9-Pas
Secondly, I released a small little trainer (a trainerette
) on
RsaPROG and Connexctix BBS mail, also on the ASPHYXIA BBS as COPPERS.ZIP
It is a small Pascal program demonstrating how to display copper bars in
text mode. Also includes a check for horizontal retrace (A lot of people
wanted it, that is why I wrote the program) (ASPHYXIA ... first with the
trainer goodies aargh, sorry, had to be done ))
Thirdly, sorry about the problems with Tut 8! If you had all the checking on, the tutorial would probably die on the first points. The reason is this : in the first loop, we have DrawPoints then RotatePoints. The variables used in DrawPoints are set in RotatePoints, so if you put RotatePoints before DrawPoints, the program should work fine. Alternatively, turn off error checking 8-)
Fourthly, I have had a surprisingly large number of people saying that "I get this, like, strange '286 instructions not enabled' message! What's wrong with your code, dude?" To all of you, get into Pascal, hit Alt-O (for options), hit enter and a 2 (for Enable 286 instructions). Hard hey? Doesn't anyone EVER set up their version of Pascal?
Now, on to todays tutorial! 3D solids. That is what the people wanted, that is what the people get! This tutorial is mainly on how to draw the polygon on screen. For details on how the 3D stuff works, check out tut 8.
The procedure I will be using here is based on something most of us learned in standard eight ... I think. I seem to recall doing something like this in Mrs. Reids maths class all those years ago ;)
Of course, it's not as simple as that. We have to make sure we only check those y lines that contain the polygon (a simple min y, max y test for all the points). We also have to check that the line we are calculating actually extends as far as where our current y is (check that the point is between both y's). We have to compare each x to see weather it is smaller then the minimum x value so far, or bigger then the maximum (the original x min is set as a high number, and the x max is set as a small number). We must also check that we only draw to the place that we can see ( 0-319 on the x ; 0-199 on the y (the size of the MCGA screen))
To see how this looks in practice, have a look at the sample code provided. (Mrs. Reid would probably kill me for the above explanation, so when you learn it in school, split it up into thousands of smaller equations to get the same answer ;))
Okay, that's it! What's that? How do you draw a vertical line? Thats simple ...
[Edit this page] [Page history] [What links here] [Discuss this topic] [Printer Friendly]
DenTut9-Pas
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 9 ]==--
- Introduction
Secondly, I released a small little trainer (a trainerette
) on
RsaPROG and Connexctix BBS mail, also on the ASPHYXIA BBS as COPPERS.ZIP
It is a small Pascal program demonstrating how to display copper bars in
text mode. Also includes a check for horizontal retrace (A lot of people
wanted it, that is why I wrote the program) (ASPHYXIA ... first with the
trainer goodies aargh, sorry, had to be done ))Thirdly, sorry about the problems with Tut 8! If you had all the checking on, the tutorial would probably die on the first points. The reason is this : in the first loop, we have DrawPoints then RotatePoints. The variables used in DrawPoints are set in RotatePoints, so if you put RotatePoints before DrawPoints, the program should work fine. Alternatively, turn off error checking 8-)
Fourthly, I have had a surprisingly large number of people saying that "I get this, like, strange '286 instructions not enabled' message! What's wrong with your code, dude?" To all of you, get into Pascal, hit Alt-O (for options), hit enter and a 2 (for Enable 286 instructions). Hard hey? Doesn't anyone EVER set up their version of Pascal?
Now, on to todays tutorial! 3D solids. That is what the people wanted, that is what the people get! This tutorial is mainly on how to draw the polygon on screen. For details on how the 3D stuff works, check out tut 8.
- How to draw a polygon
The procedure I will be using here is based on something most of us learned in standard eight ... I think. I seem to recall doing something like this in Mrs. Reids maths class all those years ago ;)
Take two points, x1,y1 and x2,y2. Draw them :
+ (x1,y1)
\
\ <-- Point a somewhere along the line
\
+ (x2,y2)
Right, so what we have to do is this : if we know the y-coord of a, what
is it's x-coord? To prove the method we will give the points random
values.
+ (2,10)
\
\ <-- a.y = 12
\
+ (15,30)
Right. Simple enough problem. This is how we do it :
(a.y-y1) = (12 - 10) {to get a.y as though y1 was zero}
- (x2-x1) = *(15 - 2) {the total x-length of the line}
For example : Two lines going down :
+ +
/ <-x1 x2->| <--For this y line
/ |
+ +
Find x1 and x2 for that y, then draw a line between them. Repeat for all
y values.Of course, it's not as simple as that. We have to make sure we only check those y lines that contain the polygon (a simple min y, max y test for all the points). We also have to check that the line we are calculating actually extends as far as where our current y is (check that the point is between both y's). We have to compare each x to see weather it is smaller then the minimum x value so far, or bigger then the maximum (the original x min is set as a high number, and the x max is set as a small number). We must also check that we only draw to the place that we can see ( 0-319 on the x ; 0-199 on the y (the size of the MCGA screen))
To see how this looks in practice, have a look at the sample code provided. (Mrs. Reid would probably kill me for the above explanation, so when you learn it in school, split it up into thousands of smaller equations to get the same answer ;))
Okay, that's it! What's that? How do you draw a vertical line? Thats simple ...
- Drawing a vertical line
IN : x1 , x2, y, color, where
asm
mov ax,where
mov es,ax
mov di,y
mov ax,y
shl di,8 { di:=di*256 }
shl ax,6 { ax:=ax*64 }
add di,ax { di := (y*256)+(y*64) := y*320 Faster then a
straight multiplication }
Right, now you add the first x value to get your startoff.
add di,x1Move the color to store into ah and al
mov al,color
mov ah,al { ah:=al:=color }
then get CX equal to how many pixels across you want to go
mov cx,x2
sub cx,x1 { cx:=x2-x1 }
Okay, as we all know, moving a word is a lot faster then moving a byte,
so we halve CX
shr cx,1 { cx:=cx/2 }
but what happens if CX was an odd number. After a shift, the value of
the last number is placed in the carry flag, so what we do is jump over
a single byte move if the carry flag is zero, or execute it if it is
one.
jnc @Start { If there is no carry, jump to label Start }
stosb { ES:[DI]:=al ; increment DI }
@Start : { Label Start }
rep stosw { ES:[DI]:=ax ; DI:=DI+2; repeat CX times }
Right, the finished product looks like this :
Procedure Hline (x1,x2,y:word;col:byte;where:word); assembler;
{ This draws a horizontal line from x1 to x2 on line y in color col }
asm
mov ax,where
mov es,ax
mov ax,y
mov di,ax
shl ax,8
shl di,6
add di,ax
add di,x1
mov al,col
mov ah,al
mov cx,x2
sub cx,x1
shr cx,1
jnc @start
stosb
@Start :
rep stosw
end;
Done!- In closing
[ My sister and I were driving along the other day when she
asked me, what would I like for my computer.
I thought long and hard about it, and came up with the
following hypothesis. When a gets a Barbie doll, she
then wants the extra ballgown for the doll, then the
hairbrush, and the car, and the house, and the friends
etc.
When a guy gets a computer, he wants the extra memory, the
bigger hard drive, the maths co-pro, the better
motherboard, the latest software, and the bigger monitor
etc.
I told my sister all of this, and finished up with : "So as
you can see, computers are Barbie dolls for MEN!"
She called me a chauvinist. And hit me. Hard.
]
- Grant Smith
19:24
26/2/94
See you next time!
- Denthor
[Edit this page] [Page history] [What links here] [Discuss this topic] [Printer Friendly]
