Planet X3 update package - August 2020
======================================

This is the official Planet X3 update package with new versions of the
executable files from August 2020.
It contains accumulated bug fixes from the past 15 months, support for
the TNDLPT audio device, an alternative grayscale CGA mode and for the
first  time  a  beta version of  the combined  ATI Graphics Solution +
medium-resolution Tandy engine.

List of files
-------------

- DISTRO.360\PX3.COM      - engine for CGAs & HGC for smaller distro
- DISTRO.720\PX3.COM      - wrapper for PX3_CGA.COM and PX3_VGA.COM
- DISTRO.720\PX3_CGA.COM  - engine for CGA derivatives and HGC
- DISTRO.720\PX3_EGA.COM  - engine for 640x200 EGA
- DISTRO.720\PX3_MTDY.COM - engine for ATI GS and med-res Tandy
- DISTRO.720\PX3_VGA.COM  - engine for VGA/MCGA and high-res Tandy
- README.TXT              - this file

The file  DISTRO.720\PX3.COM has not been modified and is included for
completeness.

New features
------------

The most notable addition is PX3_MTDY.COM, which provides full support
for the 640x200 16-color mode of  ATI "Small Wonder" Graphics Solution
cards with  CGA screen and  experimental  support for 320x200 16-color
Tandy mode.  The latter is based  on dynamic  down-conversion from the
256-color VGA artwork to 16 colors via an auto-generated lookup table.

Furthermore, this  release adds  support for  the TNDLPT audio device,
which can  be used to  play back  Planet X3's Tandy music via parallel
port.  The TNDLPT has to be un-muted before Planet X3 is launched.

Lastly, a variant of the existing CGA 4-gray mode has been added, that
swaps the two intermediate shades of gray to accommodate to monochrome
CGA screens that otherwise would not display the four shades, propery.

Bugfixes
--------

The  following  adjustments  have been  made to correct or work around
software bugs that occured in or with previous versions of Planet X3:

- Do not show white as yellow in CGA 4-gray mode on IBM EGAs
- Use correct background colors for some text strings in VGA mode
- Restore a proper text mode when leaving high-res Tandy mode
- Work around buggy int 29h versions for "Have a nice DOS!" message

Modding hints
-------------

All executable files of notable size have been compressed with UPX and
have to be de-compressed before they can be modified in any meaningful
way.
As of this version, the output port for Tandy sound is hard-coded in a
word variable rather than in the code itself.  If you have an ISA card
that provides Tandy sound capabilities at a different output port, you
only have to find and change the correct C0 00 word.

The palette in PX3_VGA starts with 00 00 00 AA 00 00 AA 55,  while the
Tandy lookup table in PX3_MTDY starts with 00 44 66 17 33 11 55 77.
The upper  four bits of  every byte in  the Tandy lookup table contain
the closest  match,  the lower four bits contain  the currently unused
second-closest  match.   Attempts to manually tweak the LUT to improve
the visual appearance of the 320x200 Tandy mode are very welcome.

The game artwork uses ZX7 compression.   Once de-compressed,  the file
formats of Planet X3's graphics and map files are trivial.

Special thanks
--------------

I would like to thank the following  people for their contributions to
this update release:

- David Murray for the original game and source code
- Carlos Teixeira for the int 29h workaround
- Serge Defever for the TNDLPT device


Have fun!

-- Benedikt Freisen
