PCDAAD General notes
--------------------

PCDAAD is a DOS interpreter for DAAD games which uses the VGA 320x200, 
256 colours mode, unlike the original one, that was using VGA 320x200,
16 colours mode. It's also capable of usin VESA BIOS Extension(VBE) to
run in 640x400 mode (SVGA) although that would increase CPU requirements
from 8086 to 80386.

Get PCDAAD at https://www.ngpaws.com/pcdaad.

PCDAAD does not pretend to support everything that was supported in the 
original interpreters. Even the original interpreters didn't support
the same features. 

Some of the features not supported so far may become supported in future
releases, or not.

Please closely read this notes to understand the differences between this
DAAD interpreter and other DAAD interpreters :

- PCDAAD does not support CALL, GFX, SFX and MOUSE condacts.

- PCDAAD supports EXTERN calls made by MALUVA condacts XPART, XMES and 
  XMESSAGE, but in order to make them work you will need to use DRC compiler 
  v0.23 or above and use "vga256" subtarget instead of "vga". Otherwise you
  would have a message saying this target does not support that feature. 
  PCDAAD does also support normal EXTERN calls.
  
- PCDAAD requires DAAD.FNT file to be in the same folder. It is a FNT file
  made with GCS, which can be found in DAAD Ready Package, and was once part
  of SINTAC adventure engine. From that FONT, only the 8 pixels high font is
  used, the 16 pixels high font is ignored. Since version 1.6, PCDAAD also can
  load a file named DAAD.CHR, in the usual CHR format. If DAAD.FNT is not 
  found, DAAD.CHR will be loaded (if present). DAAD.FNT, as all SINTAC fonts,
  is proportional. DAAD.CHR is not, and PCDAAD defaults to understand it as a 
  6x8 charset, so you should use a font like those used in DAAD for targets
  other than C64 and CPC. You can find a valid DAAD.CHR in DAAD-Ready, at the
  ASSETS/CHARSET folder. The one named AD8x6.CHR would be the one. You can also
  find a sample of a valid DAAD.FNT file in that same folder, under the name 
  MSDOS.FNT.

- PCDAAD will run DAAD.DDB file found in same folder, created with DRC compiler.
  You can thouhg specify a different DDB file to be loaded by placing it as 
  parameter:

  PCDAAD MYGAME.DDB

- PCDAAD properly supports English and Spanish languages, but there are not separated interpreters, the interpreter will detect the language in the DDB header.

- If a file named DAAD.PCX or DAAD.VGA is found in the same folder, it will be 
  loaded as loading screen, then wait for a key to be pressed and screen cleared.
  When cleared, color 0 of the PCX palette will be used to clear, so make sure
  it is black or the color you want for background. It should be a 320x200 PCX
  file with a 256 color indexed palette.

- This interpreter uses a mode with same resolution as the CPC and C64 interpreters,
  so the structure of columns and rows is the same (40 columns, 25 rows) unlike
  the classic PC interpreter that has 53 columns and 25 rows. On the other hand,
  the columns structure is not that important in PCDAAD, as it uses a proportional
  font so in fact in those 40 columns, and with the default font, you can easily
  fit more than 53 characters per line. Thus, the column definition it's just 
  important to define the text and graphic windows size, but nothing else. When using
  DRC 0.23 or above the COLS symbol will properly store the value 40.

- "PICTURE n" condact will look for a file named n.PCX or n.VGA in the same folder,
  padded with zeroes in the left in the Maluva style (i.e. PICTURE 7 will look for
  007.VGA or 007.PCX). Images should be 256 colours indexed PCX files, width a 
  maximum size of 320x200 pixels, although making them be exactly the same size 
  the pictures window it's a good idea (otherwise they will use more disk space,
  take longer to load, and be cut anyway).

- The VGA 256 mode is a 320x200 x 256 colours mode, that uses palette. That means
  the 256 colours available don't need to be the same for all pictures, which is 
  great, but also can make the pictures look weird when you load the new picture
  palette and the previous picture is still there. Maybe that takes only 
  milliseconds, but sometimes you can see it. To avoid it, use the same palette 
  in all location pictures, or just clear the images window before loading a new
  picture.

- Also, please notice the text area is also affected by the palette. PCDAAD
  defaults to use colour 0 for background and colour 15 for INK. If those
  colours happen to be black and white in the picture you loaded, everything
  will be OK, but if them both are green, then you will see green on green
  in the text area. PCDAAD includes PCXfixer utility, which unlike PCDAAD
  is a modern tool made for macOS, Windows and linux. PCXfixer takes a PCX
  file and generates another one where color 0 is black and color 15 is white.
  If the origin file is too complicated or uses too many colors pcxfixer
  may give up and be unable to create a "fixed" PCX file. PCXfixer also allows
  you to choose other colors if you don't want white on black but other 
  combination. Run PCXfixer without parameters from the command line for more
  information.

- You can force PCDAAD to create a log of everything that happens behind the 
  scenes. The log will contain all player orders, responses, and even condacts
  being executed. It is meant for debug purposes and it will be dumped in the
  file PCDAAD.LOG, which will be overwritten in each PCDAAD execution. To
  enable verbose log add "-vlog" parameter to PCDAAD call:

  PCDAAD -vlog
  PCDAAD MYGAME.DDB -vlog

  If you just want playe input and game output, use -log instead of -vlog

  Please notice dumping every condact to the log file with the -vlog option 
  is slow, and normal games initialization can take several seconds to 
  happen. That is absolutely normal. Use -vlog only if you really need it.

- You can have diagnostics in-game, just like with Professional Adventure 
  Writer.  To enable them add "-d" parameter 

  PCDAAD -d

  Type "+" [intro] at the game prompt to know how to use them.

- Parameter -nomaluva disables Maluva emulation in EXTERN calls. May be 
  of use in the future if EXTERN becomes supported and you want to disable  
  Maluva emulation in order to have your own routines. 

- Automatic input: you can have PCDAAD go get order from a text file, 
  instead of player. This is very useful for testing purposes, like 
  checking if game still can be finished after making changes. If the
  file becomes exhausted when reading from it, PCDAAD will them ask 
  the player again. You can use -i parameter for that:

  PCDAAD -iSOLUTION.TXT

  Please notice there is no space between -i and the file name.

- PCDAAD can support nested DOALLs if they are nested in different processes, 
  but to make it support that feature you have to call interpreter with the 
  -ndoall parameter. If that parameter is absent, any DOALL call found during
  a DOALL loop will generate a runtime error #4. That runtime error will also
  happen if, despite having used the -ndoall parameter, a scond DOALL call is
  found in the same process where the first DOALL call is.

- SVGA: If PCDAAD is run with -s parameter, it will try to run in SVGA mode.
  The computer would need to support VESA mode 100 (640x400) and have a 386sx
  CPU or better, although a 486DX is recommended for performance reasons. 
  Please notice the font size will still look like in VGA, it's only the graphics
  that double resolution. Launching PCDAAD with -s parameter will force SVGA mode.

Unlike in SVGA mode, running in pure VGA 320x200 mode resolution will requiere less CPU 
power, so a 8086 should be enough, at least while it has a VGA card installed.

If you find any issues you can:

1) If you think it's a bug you can add an issue at Github:

https://github.com/Utodev/PCDAAD/issues

2) If you need help you can ask in the Retroaventuras group in
Telegram (for Spanish users) or the 8 bit text adventures group
(for English speakers).

https://t.me/RetroAventuras

https://t.me/Advent8bit

You can also find me on Twitter, but I tend to enter twitter only
now and then: @uto_dev

How to use EXTERN
-----------------
 
When "EXTERN value1 value2" is called, PCDAAD will first look wether 
Maluva emulation is enabled or not. If it is (what happens unless you call
PCDAAD with the -nomaluva parameter), then it will try first to understand
that call as a Maluva Condact. That means that in case value2 is 3 (XMES)
or 4 (XPART), PCDAAD will emulate XMES or XPART Maluva condacts, and 
exit.

Please notice from here a basic knowledge of x86 assembly code is 
expected.

If Maluva emulation is disabled, or value2 is neither 2 nor 3, then the
real EXTERN will be executed.
    
When real EXTERN is run, it will look for a file named DAAD.EXT in the 
hard disk, and if found, it will load it to RAM. DAAD.EXT should be a 
pure machine code binary, that is, it should be something like a .COM 
file, not like a .EXE file which has a header.

When called, PCDAAD will first put the following information in registers,
then call your external code:

  AL = EXTERN first parameter 
  AH = EXTERN second parameter 
  DS:BX = pointer to the flags table (256 values)
  DS:CX = pointer to the object locations table (256 values too, some may be 
          unused)

Make sure your code preserves DS, CS and SS values.

This would be a minimal EXTERN code, that just sets flag 100 to "value1" (EXTERN first parameter):
  
  PUSH BP
  MOV BP,SP ; header

  MOV [BX+100], AL 

  MOV SP,BP ; exit
  POP BP
  RETF

Please notice the DAAD.EXT file will only be loaded once, on first EXTERN
execution, which means EXTERN calls will be fast if your code is fast,
except the first one. It also means that in case you have variables in
your code, they will keep values between code execution.

If you want some value to be saved with the savegames, you can use the are not 
used by your specific game in the objects locations table (DS:CX), as the 
whole table, 256 bytes, is saved with the savegames, no matter if there game
has 1 object or 200. If you are making a EXTERN to be used by others, and you 
don't know how many objects the games will have, the best way to do it is 
writing your data at the end of object locations table (where object 255, 254,
253, etc.)

Executables as EXTERNS
----------------------
If you run PCDAAD with -exec parameter, PCDAAD wil try to run executable files
to perform extern code. Basically, first parameter of EXTERN will be used as
filename, and if a matching EXE, COM or BAT file is found (in that specific 
order) then it's run.

Second parameter of EXTERN will be passed as first parameter to that executable,
and two parameters more will follow with the address of the flags in RAM, and
the address of the object locations.

Have in mind the executable will be loaded into lower RAM, so it cannot be too big 
in order for PCDAAD and the exec fit simultaneously.

Example: "EXTERN 12 89" will try to find 12.EXE, then 12.COM then 12.BAT and if
for instance it founds 12.COM, it will run the command:

12.COM 89 <flags address> <object locations address>