Scrolling

                    嬪様様様様様様様様様様様様様様様
                             W E L C O M E         
                      To the VGA Trainer Program    
                                  By                
                          DENTHOR of ASPHYXIA        
                    塒様様様様様様様様様様様様様様様  
                      陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳 
                        陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳

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

  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.

 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
                            Natal
             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!

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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).

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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?

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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.

 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
   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
 {$X+} {$R-}
 Uses Crt;

 CONST VGA = $a000;
       XSize = 16;
       YSize = 16;

 TYPE
         Letter = Array[1..xsize,1..ysize] of Byte;
         Letters = Array[' '..']'] of Letter;

 VAR Font : ^Letters;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure SetMCGA;  { This procedure gets you into 320x200x256 mode. }
 BEGIN
   asm
      mov        ax,0013h
      int        10h
   end;
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure SetText;  { This procedure returns you to text mode.  }
 BEGIN
   asm
      mov        ax,0003h
      int        10h
   end;
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 procedure WaitRetrace; assembler;
   { This waits until you are in a Verticle Retrace }

 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 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;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure PutPixel (X,Y : Integer; Col : Byte; Where : Word);
    { This puts a pixel at X,Y using color col, on VGA or the Virtual Screen}
 BEGIN
   Mem [Where:X+(Y*320)]:=col;
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 procedure LoadPal (FileName : string);
    { This loads the Pallette file and puts it on screen }
 type DACType = array [0..255] of record
                                 R, G, B : byte;
                               end;
 var DAC : DACType;
     Fil : file of DACType;
     I : integer;
 BEGIN
   assign (Fil, FileName);
   reset (Fil);
   read (Fil, DAC);
   close (Fil);
   for I := 0 to 255 do Pal(I,Dac[I].R,Dac[I].G,Dac[I].B);
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 function Exist(FileName: string): Boolean;
     { Checks to see if filename exits or not }
 var f: file;
 begin
   {$I-}
   Assign(f, FileName);
   Reset(f);
   Close(f);
   {$I+}
   Exist := (IOResult = 0) and
    (FileName <> '');
 end;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure Setup;
   { This loads the font and the pallette }
 VAR f:file;
     loop1:char;
     loop2,loop3:integer;
 BEGIN
   getmem (font,sizeof (font^));
   If exist ('softrock.fnt') then BEGIN
     Assign (f,'softrock.fnt');
     reset (f,1);
     blockread (f,font^,sizeof (font^));
     close (f);
     Writeln ('SoftRock.FNT from TEXTER5 found in current directory. Using.');
   END
   ELSE BEGIN
     Writeln ('SoftRock.FNT from TEXTER5 not found in current directory.');
     For loop1:=' ' to ']' do
       For loop2:=1 to 16 do
         for loop3:=1 to 16 do
           font^[loop1,loop2,loop3]:=loop2;
   END;
   If exist ('pallette.col') then
     Writeln ('Pallette.COL from TEXTER5 found in current directory. Using.')
   ELSE
     Writeln ('Pallette.COL from TEXTER5 not found in current directory.');
   Writeln;
   Writeln;
   Write ('Hit any key to continue ...');
   readkey;
   setmcga;
   If exist ('pallette.col') then loadpal ('pallette.col');
 END;

 {陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳陳}
 Procedure ScrollMsg (Msg : String);
   { This scrolls the string in MSG across the screen }
 Var Loop1,loop2,loop3 : Integer;
 Begin
   For loop1:=1 to length (msg) do BEGIN
     For loop2:=1 to xsize do BEGIN

       { This bit scrolls the screen by one then puts in the new row of
         letters }

       waitretrace;
       For Loop3 := 100 to 99+ysize do
         move (mem[vga:1+(loop3*320)],mem[vga:(loop3*320)],319);
       for loop3:=100 to 99+ysize do
         putpixel (319,loop3,font^[msg[loop1],loop2,loop3-99],vga);
            { Change the -99 above to the minimum of loop3-1, which you
              will change in order to move the position of the scrolly }
     END;

     {This next bit scrolls by one pixel after each letter so that there
       are gaps between the letters }

     waitretrace;
     For Loop3 := 100 to 99+ysize do
       move (mem[vga:1+(loop3*320)],mem[vga:(loop3*320)],319);
       for loop3:=100 to 99+ysize do
         putpixel (319,loop3,0,vga);
   END;
 End;

 BEGIN
   ClrScr;
   Writeln ('This program will give you an example of a scrolly. If the file');
   Writeln ('SOFTROCK.FNT is in the current directory, this program will scroll');
   Writeln ('letters, otherwise it will only scroll bars. It also searches for');
   Writeln ('PALLETTE.COL, which it uses for it''s pallette. Both SOFTROCK.FNT');
   Writeln ('and PALLETTE.COL come with TEXTER5.ZIP, at a BBS near you.');
   Writeln;
   Writeln ('You will note that you can change what the scrolly says merely by');
   Writeln ('changing the string in the program.');
   Writeln;
   Setup;
   repeat
     ScrollMsg ('ASPHYXIA RULZ!!!   ');
   until keypressed;
   Settext;
   freemem (font, sizeof (font^));
   Writeln ('All done. This concludes the fifth sample program in the ASPHYXIA');
   Writeln ('Training series. You may reach DENTHOR under the name of GRANT');
   Writeln ('SMITH on the MailBox BBS, or leave a message to ASPHYXIA on the');
   Writeln ('ASPHYXIA BBS. Get the numbers from Roblist, or write to :');
   Writeln ('             Grant Smith');
   Writeln ('             P.O. Box 270');
   Writeln ('             Kloof');
   Writeln ('             3640');
   Writeln ('I hope to hear from you soon!');
   Writeln; Writeln;
   Write   ('Hit any key to exit ...');
   Readkey;
 END.

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Date this article was posted to GameDev.net: 7/16/1999
(Note that this date does not necessarily correspond to the date the article was written)

See Also:
Denthor's Asphyxia Tutorials

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