Tuesday, 7 September 2021

Galaxian Part 7 - Preliminary Impressions

Whilst I've been waiting for Miro to digest the previous posts and hopefully develop his framework to the point I have described, I've actually been doing a little bit of the transcode. I'm not going to go into any specifics here as I'd like to document it in some form of ordered fashion, but I will make a few observations, if for no reason other than hinting that I haven't yet abandoned the project.

If there was ever any shadow of a doubt that Scramble was based on the Galaxian codebase (and there really wasn't), it is beyond question in my mind now.

It of course helps that Scott Tunstall reverse-engineered both games - and hence the disassemblies use common terminologies and labels - but there are plenty of instances where those identically-named variables actually share the same address in both games.

Despite having transcoded only a handful of routines thus far, I've already encountered common code. And it's very clear that both games also share the overall architecture of the code. It's an absolute certainty that Scramble code was derived from the Galaxian codebase.

Now that bodes well for the project. Aside from the obvious advantages that a familarity with the architecture presents, I can also say with confidence that the assembler code lends itself very nicely to a higher level implementaion. And that's certainly not true of all assembly code.

And touching on the subject of process I discussed in Part 5, I'm happy so far with how things are turning out when preserving the original assembly code interleaved with the C code. During the course of this blog I'll be posting examples to illustrate various aspects of the transcode, and you can make your own mind up, but I think it adds more than it detracts from, for example, the 'cleanliness' of the higher level source file.

At this stage of the transcode, particularly given the architecture of Galaxian, there is a lot of tedious typing to be done; defining functions and their prototypes, adding variables to the working RAM structure, defining tables etc. I'll likely press on with this aspect of the transcode whilst waiting for Miro, so I can't at this point say when I'll post the next blog entry.

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