Short: HD Installer for Gyrex / Pursuit to Earth
Author: DJ Mike (djmike@crystalmike.com)
Version: 1.0
Type: game/patch
Requires: WHDLoad 19, 364k chip mem, 4k any mem

This patch applies to "Gyrex" aka "Pursuit To Earth"
© 1988 Powerhouse Software Ltd.

Both versions of the game are supported.

REQUIREMENTS

- Original disk or compatible disk image
  (Cracks have not been tested and are not supported)
- Slave requires WHDLoad 19+
- Game requires 364k chip memory, plus 4k any memory
  (+ approx 730k other memory for preload option)

FEATURES

- Game loads fully from HD
- Quit game at any time (default key F10), including on 68000 machines
- OS calls removed
- Missing blitter wait fixed
- CPU-dependent (empty DBF) loops fixed
- Access fault on defeating boss fixed (movem.w sign extension bug)
- Stack moved to fast memory if available
- Can enable caches for faster speed
- Trainer/other options added - set CUSTOM1 with any of the following:
  + 1 for infinite lives
  + 2 for ship immune to damage
  + 4 for power-ups immune to damage
  + 8 to enable cheat keys (screen flashes blue for on, red for off):
    * DEL to skip level
    * HELP to give 69 lives + all powerups (same as game's HELP+M+E cheat)
- Set CUSTOM2=0-11 to select starting world (set of 4 waves)
- Set CUSTOM3 to number of frames to wait, to regulate speed
- CD32 controls added - set CUSTOM4=1 to enable:
  * Blue button uses selected power-up
  * Shoulder buttons+Yellow quits game
- Combined Color/New/Rom Icon included
- Source code included

CHEAT

Hold HELP+M+E (HELP ME) at the same time to grant 69 lives + all power-ups.
If cheat keys are enabled, you only need to press HELP.

HISTORY

Version 1.0 (2025-10-21)
- Initial release

WORDS FROM THE AUTHOR

This install was by special request! One of its developers, Steve Benfield,
got in touch with an original disk of the game as it was called when he knew
it: Gyrex, a Gyruss clone programmed by Jason Chown that would later go on
to be released - credit removed - as Pursuit to Earth.

The disk was rescued from a mountain of decaying Amiga things in a collapsed
shed, of all places, that had long been forgotten about. As Steve told me,
"The disks and the machine [had been temporarily moved] to a garden shed due
to a leaking roof. The machine and the disk collection was forgotten during
this time and the shed collapsed in a storm.

"Many years later it was discovered. The machine was a corroded mess and the
disks exposed to the elements - wet, mouldy and covered in bird droppings.
These disks were painstakingly salvaged one by one... about 3,000 of them.
Many did not rotate as disc was stuck to the internal jacket. Gyrex was one
of many of these disks that was snatched back from the dead."

That so little has been known about the development of Pursuit to Earth has
raised questions. It seems the game was actually made by a studio called
Powerhouse Software Ltd. (only credited as 'PDG' the final game).

In Steve's words: "I started out my software career at Incentive Software
and then joined APS (Argus Press Software) that had acquired the likes of
Quicksilva, Bug Byte, Mindgames, A&F and countless others. APS was bought
out by Grandslam and I left to setup Powerhouse with an old friend. We just
got started and charted a few titles when the software bubble burst and a
lot of publishers went down. We shelved what we had waiting for better
times, but we had all moved on to do our own thing. Gyrex was one of 3
titles looking publishers and no one was commissioning new titles. There
maybe some more stuff floating around if I can salvage the disks.

"Most work in software house was commissioned. And sometimes someone had a
project idea and we would see if we could find an interested publisher.
In the case of Gyrex it was an in house project looking for a publisher that
never came. Once a publisher was found it would have been tweaked, branded
and some rework to fit in with the storyboard the publisher had in mind.

"I assume Jason sold it on years later and I hope he did. Equally a 
publisher that had a copy could have tweaked it. The fact that PDG and not
PHS was used and Jason's name was removed sounds like someone removing
fingerprints. Who knows, it's historic and it is what it is. And 4 years
down the road who cared who paid for its development when the company was
gone. So I hope it was Jason and he got something out of it."

For the install, I was able to remove the few OS calls the game does, as it
only needs the OS to generate a copperlist to display the initial picture,
and do the usual memory allocations and disk loads. All easily replicated
without resorting to KickEmu.

There was an access fault after the boss due to a use of movem.w on an
address register, which causes a sign extend and therefore a negative
address.

Although the game only runs in chip memory it can be sped up by enabling
caches, which will help with the heavy slowdowns. However, as the game can
also run too fast I have included a frame delay feature so you can set the
minimum delay between each frame (I recommend 3-4 for a sane experience!).
Only the main gameplay has this cap applied - elsewhere the frame rate is
set at 25fps. (Unless frame delay is switched off, in which case everything
is left uncapped.)

I've also added 2nd button support to trigger power-ups, and a selection
of trainers because the game is quite hard!

A special thanks to Steve for supplying the original version of this game,
and for our fascinating correspondence about this piece of Amiga history.

Enjoy! :-)

--- DJ Mike (21st October 2025)

         Bug report form, full WHDLoad package and other installs:
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PERFORMANCE OF THE PACKAGE IS ASSUMED BY YOU AND IF THE PACKAGE SHOULD PROVE
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THIRD PARTY HAS BEEN POINTED AT SUCH POSSIBILITIES OF DAMAGE.