BBC Micro cassette Elite | BBC Micro disc Elite | 6502 Second Processor Elite | BBC Master Elite | Acorn Electron Elite | NES Elite | Elite-A | Teletext Elite | Elite Universe Editor | Elite Compendium | Elite over Econet | Flicker-free Commodore 64 Elite | BBC Micro Aviator | BBC Micro Revs | Archimedes Lander

This repository contains a patched version of Commodore 64 Elite that drastically improves the quality of the graphics. It does this by removing most (but not all) of the flicker from the ship-drawing and planet-drawing routines. It also contains a patched version for the Commodore Plus/4.

You can see the difference it makes in the following clip. The patched version is on the left, and the original version is on the right:

• To play the flicker-free version, see the sections on playing flicker-free Commodore 64 Elite and playing flicker-free Commodore Plus/4 Elite.

• To read about how the patch weaves its magic, see the section on how the patch works.

• If you are interested in building and applying the patch yourself, see the section on building the patch.

The ship-drawing code in the patch has been backported from the BBC Master version of Elite, so this part is 100% Bell & Braben code that's making its first appearance on the Commodore 64. The improved planet-drawing code is by Mark Moxon, and takes the same algorithm and applies it to the planets, with additional code to reduce flicker even further. The algorithm is not perfect - planets still flicker slightly when partially off-screen, for example - but it is a big improvement on the original, very flickery release.

To see the flicker-free planets in all their glory, I recommend you enable detailed planets by pausing the game, pressing "P" (you will hear a confirmation beep), and unpausing. Planets will then have craters, meridians and equators... though note that this does slow things down a bit, which is why it is disabled by default.

• Acknowledgements

  • A note on licences, copyright etc.

• Playing flicker-free Commodore 64 Elite

• Playing flicker-free Commodore Plus/4 Elite

• How the patch works

  • A better algorithm
  • The patching process
  • Patching the Commodore Plus/4 version

• Building the patch

  • Requirements
  • Applying the patch

Commodore 64 Elite was written by Ian Bell and David Braben and published by Firebird, and is copyright © D. Braben and I. Bell 1985.

BBC Master Elite was written by Ian Bell and David Braben and is copyright © Acornsoft 1986.

The code in the flicker-free patch was reconstructed from a disassembly of the BBC Master version released on Ian Bell's personal website.

The Commodore 64 game disks in this repository are very similar to those released on Ian Bell's personal website, but to ensure accuracy to the released versions, I've used disk images from the Commodore 64 Preservation Project (it turns out that the disk images on Ian Bell's site differ slightly from the official versions). The Commodore Plus/4 version is based on the disk image from Ian Bell's site.

The commentary is copyright © Mark Moxon. Any misunderstandings or mistakes in the documentation are entirely my fault.

Huge thanks are due to the original authors for not only creating such an important piece of my childhood, but also for releasing the source code for us to play with. Also, a big thumbs up to Kroc Camen for his epic Elite Harmless project, which is a really useful reference for anyone exploring the C64 binaries. Finally, thanks to the gurus in this Lemon64 forum thread for their sage advice.

For the Commodore Plus/4 version, I am indebted to @Kekule1025 on Twitter, who extracted the original game from Pigmy's binaries, and wrapped it back up once I had finished adding the patch. Thank you Kekule.

You can find more information about my own Elite project in the fully documented source code for Elite on the BBC Micro.

This repository is not provided with a licence, and there is intentionally no LICENSE file provided.

According to GitHub's licensing documentation, this means that "the default copyright laws apply, meaning that you retain all rights to your source code and no one may reproduce, distribute, or create derivative works from your work".

The reason for this is that my patch is intertwined with the original Elite game code, and the original game code is copyright. The whole repository is therefore covered by default copyright law, to ensure that this copyright is respected.

Under GitHub's rules, you have the right to read and fork this repository... but that's it. No other use is permitted, I'm afraid.

My hope is that the educational and non-profit intentions of this repository will enable it to stay hosted and available, but the original copyright holders do have the right to ask for it to be taken down, in which case I will comply without hesitation. I do hope, though, that along with the various other disassemblies, commentaries and disk images of Elite, it will remain viable.

To play the flicker-free version of Commodore 64 Elite, you need to download a disk image and load it into an emulator or a real machine. Just like the original game, the flicker-free version is available in two distinct flavours: PAL and NTSC.

• Download flicker-free Commodore 64 Elite (PAL) as a .d64 disk image - this is the best version to use for emulators and most European machines

• Download flicker-free Commodore 64 Elite (NTSC) as a .d64 disk image - this is the best version to use for most machines from the Americas

See here for a brief technical summary on the differences between PAL and NTSC on the Commodore 64.

All these images have been tested in the VICE emulator and in a number of online emulators, such as C64 online and Virtual Consoles. They should also work on real machines. If you don't know which one to use, try the PAL version first, as that seems to be the default setting for most emulators.

The disk images are based on the GMA86 release of Elite from 1986, so saved commander files should work in exactly the same way as in the original GMA86 version. The only changes in the patch are graphical, and they don't affect gameplay in any way.

To see the flicker-free planets in all their glory, I recommend you enable detailed planets by pausing the game, pressing "P" (you will hear a confirmation beep), and unpausing. Planets will then have craters, meridians and equators... though note that this does slow things down a bit, which is why it is disabled by default. You can pause the game with INST/DEL and unpause it with <- (which are typically mapped to backspace and Home in emulators like VICE).

To play the flicker-free version of Commodore Plus/4 Elite, you can either download a PRG file and load it into an emulator or a real machine, or you can play it online in your browser:

• Download flicker-free Commodore Plus/4 Elite as a .prg file - this is the best version to use for emulators and real machines

• Play Commodore Plus/4 Elite in your browser - this is the quickest way to get playing

The PRG file has been tested in the VICE emulator and the YAPE emulator. It should also work on real machines.

The Plus/4 version is based on Pigmy's release, so saved commander files should work in exactly the same way as in the original. The only changes in the patch are graphical, and they don't affect gameplay in any way.

To see the flicker-free planets in all their glory, I recommend you enable detailed planets by pausing the game, pressing "P" (you will hear a confirmation beep), and unpausing. Planets will then have craters, meridians and equators... though note that this does slow things down a bit, which is why it is disabled by default. You can pause the game with INST/DEL and unpause it with <- (which are typically mapped to backspace and Home in emulators like VICE).

The 1986 releases of Elite on the BBC Master and Apple II show a marked improvement in the quality of the wireframe graphics when compared to earlier versions. This is down to an improved algorithm that seriously reduces flicker without slowing down the game.

In the original 1984 and 1985 versions of Elite, such as those for the BBC Micro, Acorn Electron and Commodore 64, ships are animated on-screen by first erasing them entirely, and then redrawing them in their new positions. The improved algorithm in the BBC Master and Apple II versions is similar, but instead of erasing the entire ship and then redrawing a whole new ship, it erases one line of the old ship and immediately redraws one line of the new ship, repeating this process until the whole ship gets redrawn, one line at a time. This interleaving of the line-drawing process results in much smoother ship graphics, and without adding any extra steps, so it doesn't affect the game speed. Ships, stations, asteroids, missiles and cargo canisters are much improved, as you can see in this clip of Lave station. The patched version is on the left, and the original version is on the right:

Note that this fix doesn't apply to Elite on Z80-based computers, such as the ZX Spectrum and Amstrad CPC. These were complete rewrites that have totally different drawing routines, and they didn't inherit the flicker of the original 6502 versions.

Planet flicker is also improved by this patch. Planets use a completely different set of drawing routines to ships, but I have applied the same improved algorithm to the ball line heap, and have added logic that ensures we only erase and redraw lines that move. Planets do still flicker a bit, especially when they are partially off-screen, but there is still a big improvement over the original.

For more information on flicker-free Elite, see the hacks section of the accompanying website.

In order to patch Commodore 64 Elite to use the new flicker-free algorithm, we have to do the following:

• Extract the game binaries from the original Commodore 64 .g64 disk image (using c1541 from the VICE emulator)

• Assemble the additional code that's required for flicker-free ships (using BeebAsm as the extra code is taken from the BBC Master version of Elite)

• Inject this new code into the game binaries and disable any copy protection code (using Python)

• Create a new disk image containing the modified flicker-free binaries (using c1541 once again)

To find out more about the above steps, take a look at the following files, which contain lots of comments about how the process works:

• The build.sh script controls the build. Read this for an overview of the patching process.

• The elite-flicker-free.asm file is assembled by BeebAsm and produces a number of binary files. These contain the bulk of the code that implements the flicker-free algorithm. These code blocks are saved as binary files that are ready to be injected into the game binary to implement the patch.

• The elite-modify.py script modifies the game binaries and applies the patch. It does this by:

  • Loading each binary into memory in turn (gma4, gma5 and gma6)
  • Decrypting it
  • Patching it by injecting the output from BeebAsm and making a number of other modifications to the code
  • Encrypting the modified code
  • Saving out the encrypted and modified binary
  • Disabling any copy protection from the original disk

The commentary in these files is best read alongside the code changes, which are described in the article on technical information for flicker-free Elite.

The Commodore Plus/4 version of Elite is an unofficial release of the game that was converted from the Commodore 64 version by Pigmy. You can find lots of information about the game on Commodore Plus/4 World.

The patching process follows a similar set of steps to the Commodore 64 version, but it operates on a game binary that's already been extracted from Pigmy's original version (thank you to @Kekule1025 for doing this, and for packing the final game up after I'd done my patching). You can access the unencrypted game using a monitor or debugger, by setting an execution breakpoint for address $5100 and loading the original Pigmy version; when the breakpoint is hit, the game will be unencrypted in memory from address $1100 onwards. This is the version that the patch scripts work with.

The game runs at a different address to the Commodore 64 version, so the elite-flicker-free-plus4.asm and elite-modify-plus4.py files modify the code in different places to the Commodore 64 version. Most (though not all) routines run at addresses that are $0900 higher in memory than their Commodore 64 counterparts, so that's why you can see the likes of + $08F0 and + $0900 throughout these files.

Also, because the Pigmy version comes with a demo loading screen that takes up a fair amount of extra memory, we can't just tack the flicker-free routines onto the end of the game binary, as we do in the Commodore 64 version. Instead we can put them in the spite area, and specifically over the top of the two Trumble sprites and the explosion sprite, which are not used in the Plus/4 version. The Plus/4 does contain Trumbles, but because the machine does not support hardware sprites, they do not appear on-screen, so the sprite definitions are unused and we can use the space to store the flicker-free routines.

However, we can't use the entire sprite area for the flicker-free patch, as the laser sight sprite definitions are still used; they aren't used as sprites, but are instead poked directly into screen memory to change the laser sights for the four types of laser. Reusing the first part of the sprite area for the flicker-free patch would therefore corrupt the laser sights, so we can only overwrite the explosion and Trumble sprites.

It turns out that this isn't quite enough space for the flicker-free planet code, so to add these routines, we have to look further afield. Luckily the Plus/4 version contains a long string of NOPs in the heart of the routine that plots the Trumble sprites on-screen, and no code jumps into these NOPs, so we can stick a JMP instruction at the start of this section, followed by the remainder of the patch routines. We also need to pack some more patch routines into the space after our patched WPLS2 routine, which is a lot shorter than in the original, and therefore has room for three of the smaller patch routines. It's a bit like a patchwork jigsaw puzzle, but it fits... just. You can see all these shenanigans in the elite-flicker-free-plus4.asm and elite-modify-plus4.py files.

The build process for the Plus/4 creates a file called elite_+4_modified.prg in the work folder that contains the modified game (you can load this into an emulator, and run it with a SYS 20736 command, as the game code starts at $5100). The downloadable version is wrapped in an updated version of Pigmy's original demo and packing code, which is a process that is out of the scope of this site (to be honest, I don't know how @Kekule1025 did it - you'll have to ask them!).

Apart from these differences, the patching process is the same as for the Commodore 64 version.

If you want to apply the flicker-free patch to Commodore 64 Elite yourself, or you just want to explore the patching process in more detail, then you will need the following:

• A Mac or Linux box. The process may work on the Windows Subsystem for Linux, but I haven't tested it.

• BeebAsm, which can be downloaded from the BeebAsm repository. You will have to build your own executable with make code.

• Python. Both versions 2.7 and 3.x should work.

• c1541 from the VICE emulator, which can be downloaded from the VICE site.

Given these, let's look at how to patch Commodore 64 Elite to get those flicker-free ships.

The patching process is implemented by a bash script called build.sh in the root folder of the repository. If any of BeebAsm, Python or c1541 are not on your path, then you can either fix this, or you can edit the $beebasm, $python or $c1541 variables in the first three lines of build.sh to point to their locations.

You also need to change directory to the repository folder (i.e. the same folder as build.sh), and make sure the build.sh script is executable, with the following:

cd /path/to/c64-elite-flicker-free
chmod a+x build.sh

All being well, doing the following:

./build.sh

will produce two disk images in the flicker-free-disks folder, and a PRG for the Commodore Plus/4 in the work folder. The disk images contain the patched Commodore 64 game, one for PAL and one for NTSC, which you can then load into an emulator or real machine. The PRG contains the patched Commodore Plus/4 game, ready to be repacked with Pigmy's code.

The build process also verifies the results against binaries that are known to be correct, which helps with debugging. Any BeebAsm log files and interim binaries are saved in the work folder during compilation, which can be useful if you want to investigate the modified binary files from each of the build steps.

Right on, Commanders!

Mark Moxon