I think the main problem is the time point you use to sample the video shift register data which maybe slightly different from ZX80 and ZX81 and some clones as well. Due to very fast access times it should be possible to sample this data maybe a half clock cycle earlier as modern SRAMS have access times of 70 or 55ns and deliver the addressed pixel data much faster than a usual ZX81. Not sure if such a ctrl can be made easily but in my eyes would need much logic in a CPLD (1 or 2 macrocells only).
Having a back porch on the green channel would be nice if you ever decide to change anything on a second batch. But all up to you, just a proposal.
It builds upon the disassembly I produced of Mazogs and the subsequent flicker-free conversion I created for the ZX80 that converted the BASIC program into equivalent machine code.
The colour scheme for the conversion is based upon that used in the game Maziacs, which was Don Priestley's adaption of Mazogs for the Spectrum.
Colour Rocket Man can be downloaded from here.
A video of the game in action can be view on YouTube.
The utility supports the generation of the loader programs for three populate UDG schemes, allowing the same character definitions to be used with other hardware as well as the Chroma interface, e.g. original Quicksilva Character Board, dk'tronics or Kayde Graphics ROM board when fitted with the optional RAM, and modern UDG interfaces that support the CHR$16/CHR$128 mechanism (a mode which Chroma currently doesn't support). This allows a replacement character set to be defined once and then shared across multiple UDG hardware interfaces. As a result other UDG interfaces can benefit from the character definitions already created for use with the Chroma interface, and when character sets are created targeting those other interfaces they could also be used with Chroma. Hence everyone can share a similar enhanced gaming experience no matter what physical UDG hardware they have.
Generated programs can be saved in a variety of formats allowing them to be easily used with Chroma, ZXC ROM cartridges, the ZXpand interface, and as cassette files for use with emulators or for loading into a real ZX81.
Character and colour definitions can be saved as XML files, allowing them to be reloaded at a later date. Since the files are in a human-readable and fully documented format, the files can easily be supported / generated by other utilities, e.g. equivalent Creator utilities written for Apple and Linux PCs.
A selection of existing character definition files for a variety of games, including a selection of fonts that can be used as the basis for creating future game character sets, can be found here. And a selection of colour definition files for a range of games can be found here.
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
The game enhancements by Villordsuch to Invasion Force (Artic Computing), Meteor Storm (dk'tronics), Galaxy Jailbreak (Romik Software) and Jetpac 81 (J. R. Todd) have all been create using forerunners of the utility to generate the loader programs. The most recent addition of Krazy Kong (PSS) was the first to be produced by using an earlier version of designer.
One thing I forgot to mention in my earlier post is that the utility produces separate loaders for applying colour and UDGs. If both options were selected and the chosen output format was as a single tzx file then when the colour loader is loaded it checks whether Chroma is present and if not then continues to load the game file. The upshot being that the same tzx file can be used with different hardware irrespective of whether Chroma colour is present or not.
QS mode doesn't use the I register and so technically a new program designed explicitly to use it could make use of the I register for another purpose...
Aside from a character designer utility that shipped with the QS Character Board board, there were 6 commercial titles that I am aware of that supported it. It seemed a shame not to allow these original programs to be seen in their full UDG glory on real hardware, which is why I supported the format in Chroma. If anyone knows of any other original titles supporting the format then I'd be keen to hear about them.