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VGA Trainer Program: part 16
Õ-------------------------------¸
| W E L C O M E |
| To the VGA Trainer Program | |
| By | |
| DENTHOR of ASPHYXIA | | |
Ô-------------------------------¾ | |
--------------------------------Ù |
--------------------------------Ù
--==[ PART 16 ]==--Introduction
Hi there. This trainer is on the scaling of an arbitrary sized bitmap to screen in two dimensions. The sample program seems to work quite quickly, and the code is document. The scaling procedure is however totally in assembler ... hopefully this won't cause to many problems.
EzE has released a trainer! It is on the speeding up of 3D for normal 3D and for virtual worlds. Check it out, it is quite good (even though I get a bit of ribbing in his quote ;-)) It will be in PCGPE ][, to be released shortly.
I have set up a mailserver (that doesn't seem to work all the time, but the ones that miss I post manually). It works like this :
Send mail to denthor@beastie.cs.und.ac.za with the subject line : request-list ... it will automatically mail you back with a list of subject lines with which you can grab certain files. You will then mail me with the subject line of a specific file and it will send you a uuencoded version of that file automatically. Cool, huh?
Remember, no more mail to smith9@batis.bis.und.ac.za, send it all to denthor@beastie.cs.und.ac.za ! Thanks.
If you would like to contact me, or the team, there are many ways you can do it :
- Write a message to Grant Smith/Denthor/Asphyxia in private mail on the ASPHYXIA BBS.
- Write to : Grant Smith P.O.Box 270 Kloof 3640 Natal South Africa
- Call me (Grant Smith) at (031) 73 2129 (leave a message if you call during varsity). Call +27-31-73-2129 if you call from outside South Africa. (It's YOUR phone bill ;-))
- Write to denthor@beastie.cs.und.ac.za in E-Mail.
- Write to asphyxia@beastie.cs.und.ac.za to get to all of us at once.
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!
What is scaling?
I think that most of you know this one already, but here goes. Let us say you have a picture (10x10 pixels) and you want to draw it to a different size (say 5x7 pixel), the process of altering the picture to fit into the new size is called scaling. Scaling only works on rectangular areas.
With scaling to can easily strech and shrink your bitmaps.
Okay, so how do we code it?
Right. The way I am going to do scaling is as follows :
For the horizontal area, I am going to calculate a certain step value. I will then trace along the bitmap, adding this step to my position, and placing the nearest pixel on to the screen. Let me explain this simpler ...
Let us say I have a 10 pixel wide bitmap. I want to squish it into 5 pixels. Along the bitmap, I would draw every second pixel to screen. In ascii :
1234567890 13579
+--------+ +---+
| | | |
| bitmap | | |dest
| | | |
+--------+ +---+As you can see, by stepping through every second pixel, I have shrunk the bitmap to a width of 5 pixels.
The equation is as follows :
step = origionalwidth / wantedwidth;Let us say we have a 100 pixel wide bitmap, which we want to get to 20 pixels.
step = 100 / 20
step = 5If we draw every fifth pixel from the original bitmap, we have scaled it down correctly! This also works for all values, if step is of type real.
We also find the step for the height in the same way.
Our horizontal loop is as follows :
For loop1:=1 to wantedwidth do BEGIN
putpixel (loop1,height,bitmap[round (curpos)],vga);
curpos:=curpos+xstep;
END;And the vertical loop is much the same. Easy huh? So east in fact, I wrote the procedure in pure assembler for you ;-) ... don't worry, it's commented.
In the sample program, instead of using reals I have used fixed point math. Refer to tut 14 if you have any hassles with fixed point, it is fairly straightforward.
I also use pseudo 3-d perspective transforms to get the positions smooth... after Tut8, this should be a breeze.
There are no new commands in the assembler for you, so you should get by with what you learned in tut7/8 ... whew! A lot of back referencing there ;) We really are building on our knowledge :)
In closing
Well, that is about it. As you can see the concept is easy, and in fact fairly obvious, but that didn't stop me from having to sit down with a pencil and a piece of paper a few months ago and puzzle it out ;-)
I have a lot of work ahead of me for a while, so this may be the last trainer for a few months ... unless I can find some free time available. So please be patient!
[ "Sir! My computer has just gone haywire!"
"What?" shouts the CO. "That is a multimilliondollar machine! find out what's wrong! This is a critical time lieutenant!"
"Yes sir"
The young lieutenant furiously types away at the keyboard, but the machine totally ignores her.
"What is going on, soldier?"
"I don't know sir! It is just doing totally arbitrary things after it's assigned tasks are completed. In the computer world this is known as Denthorisms."
The computer starts to make random beeps, and prints out a payroll program.
"Get it working NOW soldier"
The lieutenant ignores him, and contines typing. She gets partial control of the system, she can run programs, but the computer is continually running arb tasks in the background. One of the techhies who have gathered behing her suddenly cries "Hey! It's accessing the missile codes! It wants to launch them!"
The typing gathers speed, but to no avail. Another techhie says "I could disconnect the computer from the link, but that would take hours! And this thing will have the codes in under five minutes at the speed it's going!"
A smile forms on the lieutanants face, and she leans back in her chair.
"What the hell are you doing?" yells the CO. "Why have you stopped?"
Again ignoring him, the lieutenant instead turns to the techhie. "Go disconnect the machine, I know how to get you the time you need."
"How on earth will you do that? The machines going at top speed!"
She smiles again, leans forward, types in three letters and hits the carriage return. The computer grinds to a halt.
The smile breaks into a grin. "Maybe it _does_ have it's uses after all."]- Grant Smith
15:30
23-9-94
Byeeeee.....
The following are official ASPHYXIA distribution sites :
É--------------------------Ë----------------Ë-----»
|BBS Name |Telephone No. |Open |
Ì--------------------------Î----------------Î-----¹
|ASPHYXIA BBS #1 |+27-31-765-5312 |ALL |
|ASPHYXIA BBS #2 |+27-31-765-6293 |ALL |
|C-Spam BBS |410-531-5886 |ALL |
|POP! |+27-12-661-1257 |ALL |
|Soul Asylum |+358-0-5055041 |ALL |
|Wasted Image |407-838-4525 |ALL |
|Reckless Life |351-01-716 67 58|ALL |
È--------------------------Ê----------------Ê-----¼Leave me mail if you want to become an official Asphyxia BBS distribution site.
TUTPRO16.PAS
{$X+}
USES crt,gfx2;
Type Pallette = Array [0..255,1..3] of byte;
VAR virscr2:virtptr;
vaddr2:word;
{--------------------------------------------------------------------------}
Procedure LoadCELPal (FileName : String; Var Palette : Pallette);
{ This loads in the pallette of the .CEL file into the variable Palette }
Var
Fil : file;
Begin
Assign (Fil, FileName);
Reset (Fil, 1);
Seek(Fil,32);
BlockRead (Fil, Palette, 768);
Close (Fil);
End;
{--------------------------------------------------------------------------}
Procedure Init;
VAR loop1,loop2:integer;
tpal:pallette;
BEGIN
getmem (virscr2,sizeof(virscr2^));
vaddr2:=seg(virscr2^);
cls (vaddr2,0);
cls (vaddr,0);
loadcelpal ('to.cel',tpal);
for loop1:=0 to 255 do
pal (loop1,tpal[loop1,1],tpal[loop1,2],tpal[loop1,3]);
loadcel ('to.cel',virscr);
for loop1:=0 to 319 do
for loop2:=0 to 199 do
if getpixel (loop1,loop2,vaddr)=0 then
putpixel (loop1,loop2,(loop1+loop2) mod 256,vaddr);
END;
{--------------------------------------------------------------------------}
Procedure Scale (x,y,w,h,origw,origh,source,dest:word); assembler;
{ This scales the picture to the size of w and h, and places the result
at x , y. Origw and origh are the origional width and height of the
bitmap. The bitmap must start at the beginning of a segment, with
source being the segment value. The image is placed in screen at dest}
VAR jx,jy,depth,temp:word;
asm
push ds
mov ax,source
mov ds,ax
mov ax,dest
mov es,ax
mov depth,0
dec h
xor dx,dx
mov ax,origw
shl ax,6
mov bx,w
div bx
shl ax,2
mov jx,ax { jx:=origw*256/w }
xor dx,dx
mov ax,origh
shl ax,6
mov bx,h
div bx
shl ax,2
mov jy,ax { jy:=origh*256/h }
xor cx,cx
@Loop2 : { vertical loop }
push cx
mov ax,depth
add ax,jy
mov depth,ax
xor dx,dx
mov ax,depth
shr ax,8
mov bx,origw
mul bx
mov temp,ax { temp:=depth shr 8*origw;}
mov di,y
add di,cx
mov bx,di
shl di,8
shl bx,6
add di,bx
add di,x { es:di = dest ... di=(loop1+y)*320+x }
mov cx,w
xor bx,bx
mov dx,jx
mov ax,temp
@Loop1 : { horizontal loop }
mov si,bx
shr si,8
add si,ax { ax = temp = start of line }
movsb { si=temp+(si shr 8) }
add bx,dx
dec cx
jnz @loop1 { horizontal loop }
pop cx
inc cx
cmp cx,h
jl @loop2 { vertical loop }
pop ds
end;
{--------------------------------------------------------------------------}
Procedure Play;
VAR x,y,z,loop1:integer;
BEGIN
z:=114;
while keypressed do readkey;
Repeat
for loop1:=1 to 50 do BEGIN
dec (z,2);
x:=16 shl 8 div z;
y:=10 shl 8 div z; { Perspective transforms ... makes the zoom smoother }
cls (vaddr2,0);
scale (160-(x shr 1),100-(y shr 1),x,y,320,200,vaddr,vaddr2);
flip (vaddr2,vga);
END; { Scale towards you }
for loop1:=1 to 50 do BEGIN
inc (z,2);
x:=16 shl 8 div z;
y:=10 shl 8 div z; { Perspective transforms ... makes the zoom smoother }
cls (vaddr2,0);
scale (160-(x shr 1),100-(y shr 1),x,y,320,200,vaddr,vaddr2);
flip (vaddr2,vga);
END; { Scale away from you }
Until keypressed;
while keypressed do readkey;
END;
BEGIN
clrscr;
writeln ('Hokay! Here is the sixteenth tutorial! This one is on nice fast 2d');
writeln ('scaling, for any size bitmap. Just hit any key and it will scale a');
writeln ('picture up and down. Clipping is NOT performed, so the destination');
writeln ('pic MUST fit in the screen boundaries. In one zoom towards and away');
writeln ('from you there is 100 frames.');
writeln;
Writeln ('You can make many nice effects with scaling, this "bouncing" is just');
writeln ('one of them ... go on, amaze everyone with your ingenuity ;-) Also,');
writeln ('why not test your coding mettle, so to speak, by implementing clipping?');
Writeln;
writeln ('The routine could greatly be speeded up with 386 extended registers, but');
writeln ('for the sake of compatability I have kept it to 286 code. Also, this');
writeln ('routine isn''t fully optimised .. you may be able to get some speedups');
writeln ('out of it... (probably by moving the finding of DI out of the loop and');
writeln ('just adding a constant for each line ... hint hint) ;)');
writeln;
writeln ('The pic was drawn by me for Tut11, I am reusing it because I am at varsity..');
writeln ('without a mouse. :(');
writeln;
writeln;
writeln ('Hit any key to continue ... ');
readkey;
setupvirtual;
setmcga;
init;
play;
settext;
shutdown;
freemem (virscr2,sizeof(virscr2^));
Writeln ('All done. This concludes the sixteenth sample program in the ASPHYXIA');
Writeln ('Training series. You may reach DENTHOR under the names of GRANT');
Writeln ('SMITH/DENTHOR/ASPHYXIA on the ASPHYXIA BBS.I also occasinally');
Writeln ('RSAProg, comp.lang.pascal and comp.sys.ibm.pc.demos. E-mail me at :');
Writeln (' denthor@beastie.cs.und.ac.za');
Writeln ('The numbers are available in the main text. You may also write to me at:');
Writeln (' Grant Smith');
Writeln (' P.O. Box 270');
Writeln (' Kloof');
Writeln (' 3640');
Writeln (' Natal');
Writeln (' South Africa');
Writeln ('I hope to hear from you soon!');
Writeln; Writeln;
Write ('Hit any key to exit ...');
readkey;
END.
GFX2.PAS
Unit GFX2;
INTERFACE
USES crt;
CONST VGA = $A000;
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}
Procedure SetMCGA;
{ This procedure gets you into 320x200x256 mode. }
Procedure SetText;
{ This procedure returns you to text mode. }
Procedure Cls (Where:word;Col : Byte);
{ This clears the screen to the specified color }
Procedure SetUpVirtual;
{ This sets up the memory needed for the virtual screen }
Procedure ShutDown;
{ This frees the memory used by the virtual screen }
procedure flip(source,dest:Word);
{ This copies the entire screen at "source" to destination }
Procedure Pal(Col,R,G,B : Byte);
{ This sets the Red, Green and Blue values of a certain color }
Procedure GetPal(Col : Byte; Var R,G,B : Byte);
{ This gets the Red, Green and Blue values of a certain color }
procedure WaitRetrace;
{ This waits for a vertical retrace to reduce snow on the screen }
Procedure Hline (x1,x2,y:word;col:byte;where:word);
{ This draws a horizontal line from x1 to x2 on line y in color col }
Procedure Line(a,b,c,d:integer;col:byte;where:word);
{ This draws a solid line from a,b to c,d in colour col }
Procedure DrawPoly(x1,y1,x2,y2,x3,y3,x4,y4:integer;color:byte;where:word);
{ This draw a polygon with 4 points at x1,y1 , x2,y2 , x3,y3 , x4,y4
in color col }
Function rad (theta : real) : real;
{ This calculates the degrees of an angle }
Procedure Putpixel (X,Y : Integer; Col : Byte; where:word);
{ This puts a pixel on the screen by writing directly to memory. }
Function Getpixel (X,Y : Integer; where:word) :Byte;
{ This gets the pixel on the screen by reading directly to memory. }
Procedure LoadCEL (FileName : string; ScrPtr : pointer);
{ This loads the cel 'filename' into the pointer scrptr }
IMPLEMENTATION
{--------------------------------------------------------------------------}
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 (Where:word;Col : Byte); assembler;
{ This clears the screen to the specified color }
asm
push es
mov cx, 32000;
mov es,[where]
xor di,di
mov al,[col]
mov ah,al
rep stosw
pop es
End;
{--------------------------------------------------------------------------}
Procedure SetUpVirtual;
{ This sets up the memory needed for the virtual screen }
BEGIN
GetMem (VirScr,64000);
vaddr := seg (virscr^);
END;
{--------------------------------------------------------------------------}
Procedure ShutDown;
{ This frees the memory used by the virtual screen }
BEGIN
FreeMem (VirScr,64000);
END;
{--------------------------------------------------------------------------}
procedure flip(source,dest:Word); assembler;
{ This copies the entire screen at "source" to destination }
asm
push ds
mov ax, [Dest]
mov es, ax
mov ax, [Source]
mov ds, ax
xor si, si
xor di, di
mov cx, 32000
rep movsw
pop ds
end;
{--------------------------------------------------------------------------}
Procedure Pal(Col,R,G,B : Byte); assembler;
{ This sets the Red, Green and Blue values of a certain color }
asm
mov dx,3c8h
mov al,[col]
out dx,al
inc dx
mov al,[r]
out dx,al
mov al,[g]
out dx,al
mov al,[b]
out dx,al
end;
{--------------------------------------------------------------------------}
Procedure GetPal(Col : Byte; Var R,G,B : Byte);
{ This gets the Red, Green and Blue values of a certain color }
Var
rr,gg,bb : Byte;
Begin
asm
mov dx,3c7h
mov al,col
out dx,al
add dx,2
in al,dx
mov [rr],al
in al,dx
mov [gg],al
in al,dx
mov [bb],al
end;
r := rr;
g := gg;
b := bb;
end;
{--------------------------------------------------------------------------}
procedure WaitRetrace; assembler;
{ This waits for a vertical retrace to reduce snow on the screen }
label
l1, l2;
asm
mov dx,3DAh
l1:
in al,dx
and al,08h
jnz l1
l2:
in al,dx
and al,08h
jz l2
end;
{--------------------------------------------------------------------------}
Procedure 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;
{--------------------------------------------------------------------------}
Procedure Line(a,b,c,d:integer;col:byte;where:word);
{ This draws a solid line from a,b to c,d in colour col }
function sgn(a:real):integer;
begin
if a>0 then sgn:=+1;
if a<0 then sgn:=-1;
if a=0 then sgn:=0;
end;
var i,s,d1x,d1y,d2x,d2y,u,v,m,n: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 := m shr 1;
FOR i := 0 TO m DO
BEGIN
putpixel(a,b,col,where);
s := s + n;
IF not (s<m) THEN
BEGIN
s := s - m;
a:= a + d1x;
b := b + d1y;
END
ELSE
BEGIN
a := a + d2x;
b := b + d2y;
END;
end;
END;
{--------------------------------------------------------------------------}
Procedure DrawPoly(x1,y1,x2,y2,x3,y3,x4,y4:integer;color:byte;where:word);
{ This draw a polygon with 4 points at x1,y1 , x2,y2 , x3,y3 , x4,y4
in color col }
var
x:integer;
mny,mxy:integer;
mnx,mxx,yc:integer;
mul1,div1,
mul2,div2,
mul3,div3,
mul4,div4:integer;
begin
mny:=y1; mxy:=y1;
if y2<mny then mny:=y2;
if y2>mxy then mxy:=y2;
if y3<mny then mny:=y3;
if y3>mxy then mxy:=y3; { Choose the min y mny and max y mxy }
if y4<mny then mny:=y4;
if y4>mxy then mxy:=y4;
if mny<0 then mny:=0;
if mxy>199 then mxy:=199;
if mny>199 then exit;
if mxy<0 then exit; { Verticle range checking }
mul1:=x1-x4; div1:=y1-y4;
mul2:=x2-x1; div2:=y2-y1;
mul3:=x3-x2; div3:=y3-y2;
mul4:=x4-x3; div4:=y4-y3; { Constansts needed for intersection calc }
for yc:=mny to mxy do
begin
mnx:=320;
mxx:=-1;
if (y4>=yc) or (y1>=yc) then
if (y4<=yc) or (y1<=yc) then { Check that yc is between y1 and y4 }
if not(y4=y1) then
begin
x:=(yc-y4)*mul1 div div1+x4; { Point of intersection on x axis }
if x<mnx then
mnx:=x;
if x>mxx then
mxx:=x; { Set point as start or end of horiz line }
end;
if (y1>=yc) or (y2>=yc) then
if (y1<=yc) or (y2<=yc) then { Check that yc is between y1 and y2 }
if not(y1=y2) then
begin
x:=(yc-y1)*mul2 div div2+x1; { Point of intersection on x axis }
if x<mnx then
mnx:=x;
if x>mxx then
mxx:=x; { Set point as start or end of horiz line }
end;
if (y2>=yc) or (y3>=yc) then
if (y2<=yc) or (y3<=yc) then { Check that yc is between y2 and y3 }
if not(y2=y3) then
begin
x:=(yc-y2)*mul3 div div3+x2; { Point of intersection on x axis }
if x<mnx then
mnx:=x;
if x>mxx then
mxx:=x; { Set point as start or end of horiz line }
end;
if (y3>=yc) or (y4>=yc) then
if (y3<=yc) or (y4<=yc) then { Check that yc is between y3 and y4 }
if not(y3=y4) then
begin
x:=(yc-y3)*mul4 div div4+x3; { Point of intersection on x axis }
if x<mnx then
mnx:=x;
if x>mxx then
mxx:=x; { Set point as start or end of horiz line }
end;
if mnx<0 then
mnx:=0;
if mxx>319 then
mxx:=319; { Range checking on horizontal line }
if mnx<=mxx then
hline (mnx,mxx,yc,color,where); { Draw the horizontal line }
end;
end;
{--------------------------------------------------------------------------}
Function rad (theta : real) : real;
{ This calculates the degrees of an angle }
BEGIN
rad := theta * pi / 180
END;
{--------------------------------------------------------------------------}
Procedure Putpixel (X,Y : Integer; Col : Byte; where:word); assembler;
{ This puts a pixel on the screen by writing directly to memory. }
Asm
mov ax,[where]
mov es,ax
mov bx,[X]
mov dx,[Y]
mov di,bx
mov bx, dx {; bx = dx}
shl dx, 8
shl bx, 6
add dx, bx {; dx = dx + bx (ie y*320)}
add di, dx {; finalise location}
mov al, [Col]
stosb
End;
{--------------------------------------------------------------------------}
Function Getpixel (X,Y : Integer; where:word):byte; assembler;
{ This puts a pixel on the screen by writing directly to memory. }
Asm
mov ax,[where]
mov es,ax
mov bx,[X]
mov dx,[Y]
mov di,bx
mov bx, dx {; bx = dx}
shl dx, 8
shl bx, 6
add dx, bx {; dx = dx + bx (ie y*320)}
add di, dx {; finalise location}
mov al, es:[di]
End;
{--------------------------------------------------------------------------}
Procedure LoadCEL (FileName : string; ScrPtr : pointer);
{ This loads the cel 'filename' into the pointer scrptr }
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
END.
