SuperHack/SuperHack CD.bin/CODING/GRAPHICS/VGA-VUL2.ZIP/VULTURE.TXT

Text File | 1995-06-17 | 9.9 KB | 193 lines

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                               ║ ∙ PRESENTS ∙ ║
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                         Palette tricks in assembler.
───────────────────────────────────────────────────────────────────────────────
 Created By   : Vulture                  Total Files  : 7
 File Type    : VGA-intro source         Release Date : June 17th 1995
 Difficulty   : Beginners level          Filename     : VGA-VUL2.ZIP
───────────────────────────────────────────────────────────────────────────────

 Well, here's another fine source-code by Vulture. This time I will cover the
 palette. I have used a copple of these routines before (VGA-VUL1.ZIP) but I
 thought it might be usefull to explain things in detail. As always the code
 is documented but there are a few things that may need sum more explanation.
 That is what I am gonna do in this file...

 The files included should be:

     - fade.exe       =>    The executable
     - fade.asm       =>    The full source
     - picture.dat    =>    Data for picture
     - palette.dat    =>    Data for palette
     - make.bat       =>    Makes the .exe
     - vulture.txt    =>    This text (yeah:))
     - file_id.diz    =>    File description

 Hmm, there probably are sum other files in here 2. Like bbs intros and stuff
 like that... Never mind.

 Ok, here we go! The palette is what makes you see the colors you see. (wow:))
 As you probably know, we have 256 colors in MCGA mode. These colors are made
 by a combination of red, green and blue values. You just mix them together.
 These R,G,B values can reach a maximum of 63. For example: 63,63,63 gives us
 a white color and 0,0,0 gives us black. Logically 35,35,35 would give us a
 gray color. You can create various colors using the palette. A maximum of
 64*64*64=262144 combinations can be made. We choose 256 colors from these
 262144 possibilities and we have a created full palette we can use in our
 code. Wow, great huh? :)

 Well, let's say you have got a palette ready for use (like in a file). Then
 you can use various techniques to set the palette. If you want to use it for
 a picture, the simplest way to initialize it would be using the BIOS. Here
 is the code to do that. Nothing to explain here... you are just using BIOS:

    mov     ax,cs            ; Move cs into AX
    mov     es,ax            ; es points to cs (where data is located)
    mov     ax,1012h         ; Select write palette function
    mov     bx,0             ; Start at color 0
    mov     cx,256           ; Write 256 colors ( 0-255 )
    lea     dx,Palette       ; es:dx points to palette data
    int     10h              ; Call VID interrupt & set palette

 Note that I use a label Palette here. You can ofcourse use your own labels.
 Take a look at the source-code to see what I mean. I have used a file to
 store all R,G,B values. Then I use the above routine to set the palette.
 So, this is simple, eh? But only use this routine if you only want to show
 a picture. It is very slow because you are using BIOS. And BIOS is slow....
 If you want to rotate or fade the palette, you should use different methods.
 Anyway, see the source for an example of the above method.

 Well, on to the next part. We can also use internal registers to set the
 palette. This is more difficult to understand. Here we go...
 Let's suppose you have created an array with all R,G,B values in it. That
 would mean 256*3=768 values. Well, first we must have a pointer which points
 to the start of the array. Do it like this:

    lea     bp,PaletteArray  ; Load offset array

 Ok, that's easy stuff, right? On to the real work. To write the palette we
 have to use port 03c8h. This port was designed for writing the palette. We
 use dx to set the port. We also have to choose the color we want to start
 writing at. We use al to do that. Well, here's the code to do it:

    mov     dx,03c8h         ; Write register
    mov     al,0             ; Start writing at color 0
    out     dx,al            ; Give info to VGA

 This selects port 03c8h and tells the VGA that we want to start writing at
 color 0. Still easy? Well, then we have to pass all R,G,B data to the VGA.
 To do that we have to use port 03c9h. That's our data port. Now we simply
 go into a loop where we set all R,G,B values at once. First we set cx to
 768 because we want to set 768 values. Then set the port to 03c9h and go
 into the loop. Inside the loop we increase the bp pointer to point to the
 next cel. Here's the code:

    mov     cx,768           ; Do all values
    mov     dx,03c9h         ; Data register
WriteAll:
    mov     al,byte ptr [bp] ; Get the value
    out     dx,al            ; Write to VGA
    inc     bp               ; Point to next cel
    loop    WriteAll

 Well, this writes 768 values to the VGA. The total code for setting the
 palette would now look like this:

    lea     bp,PaletteArray  ; Load offset array
    mov     dx,03c8h         ; Write register
    mov     al,0             ; Start writing at color 0
    out     dx,al            ; Give info to VGA
    mov     cx,768           ; Do all values
    mov     dx,03c9h         ; Data register
WriteAll:
    mov     al,byte ptr [bp] ; Get the value
    out     dx,al            ; Write to VGA
    inc     bp               ; Point to next cel
    loop    WriteAll

 Again, this code will set the palette values found in the PaletteArray using
 the internal registers of the VGA. Fast stuff...

 Right. What if you want to READ the palette? Well, then you use port 03c7h.
 This is our read-register. Instead of grabbing a value out of the array and
 writing it to the VGA, you read it from the VGA and put it IN the array.
 But there is one trick to do here. If you read from the VGA you must be sure
 that you do not write values above 63 to the array. Remember that a palette
 value can only be between 0 and 63. Take a look at the following code:

    in      al,dx            ; Get what's in the register (read)
    and     al,00111111b     ; Mask of the upper 2 bits (value=0..63)

 Ok, I suggest you try to code your own read routine. Shouldn't be that hard
 to do. Just modify the write routine I gave you here. If you have troubles,
 just take a glance at the fully documented sourcecode provided.

 Keep in mind that there are indeed various otha ways to do this stuff. I
 only explained the way I did it myself. I could have avoided a copple of
 things but I decided to put it in there anyway. What's important is that
 you fully understand those portwrites. The way you handle it from there
 is totally up to you (hint: rep outsb).

 Well, I could ofcourse explain how the palettefading works but I let you
 figure that one out for yourself. I just don't feel like explaning it... :)
 Just play a little with the routines found here and you'll get the hang
 of it soon. Only way to learn things is by trial and error, right?

 Ok, that's all I have to say for now. Check out the .asm file and learn from
 it. Use it for yar own intros but don't just rip the code. Understand what
 you are doing. Andeh... a greet would be appreciated. Simply ripping is lame.
 But then again, if there weren't any lamerz, cewl people wouldn't have anyone
 to loose their frustations on..... :)

 Hmm, well, the following cr*p is supposed to be stated so here we go:
 I (Vulture) take no responsibility for any mistakes found in this document.
 So use at your own risk. If you spot errors or have something to add to the
 text, don't hesitate to contact me. Phew, that's that... :)

 Wanna contact Outlaw for any reason? Then leave mail at one of our distros.
 Don't hestitate to mail Outlaw, coz we like to chat with otha scene-people.

 Be seeing ya...


         Signed:    Vulture / Outlaw Triad


─────────────────────────┬───────────────────────┬────────────────────────────
 Outlaw Triad Distros :  │  Greetz from Outlaw:  │  Releases sofar:
─────────────────────────┼───────────────────────┼────────────────────────────
                         │                       │
 ■    Blue Thunder   ■   │   - DemoLisher        │   ■ MESSAGE  (dosscroller)
 ■ [phone] ■   │   - ThunderHawk       │
                         │   - Ash               │   ■ VGA-VUL1 (sources)
                         │   - The Machine       │
 ■     FireHouse     ■   │   - X∙N∙TRiC          │   ■ CHAINDOC (textfile)
 ■ [phone] ■   │   - Utter Chaos       │
                         │   - Crusher           │   ■ VGA-VUL2 (sources)
                         │                       │
                         │   - Critical          │   ■ BASICDOC (textfile)
     Open for more!      │   - Da Frisian Force  │
                         │   - Tribal            │   + various bbs-intros
                         │                       │
─────────────────────────┴───────────────────────┴────────────────────────────

                   ■ (C) 1995  O∙U∙T∙L∙A∙W   T∙R∙I∙A∙D ■

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