Thursday, 26 June 2014

C-ing things clearer

I've been working on the Lode Runner C port rather than tackle the disk issues on the Coco3... thought I'd let people do some beta-testing for me whilst I psych myself up to finish it.

My weapon of choice is the Allegro graphics library on Windows 7, only because I'm familiar with it. As it turns out, it's looking like it's not quite suited to the task - or perhaps more likely I can't drive it properly. Attempts to create a virtual screen for page flipping (yes, I know it's frowned upon) have resulted in crashes. But I can hack enough to see both screens at once. There are also sprite issues with ugly hacks atm.

As I am interested in preserving the 'style' of the original implementation, I've used more goto's in this one piece of code than I have in my entire history of C programming up until this point. Most of the code can be implemented in functions, but the higher-level routines are sufficiently convoluted that any attempt to structure them will invariably result in subtle differences in behaviour - not to mention no longer resemble the original code. In any case, there's only a few routines with goto's but each of those few use them quite liberally.

The rest of it hasn't been too painful up until this point. I know it's second-time around for me, but some of the routines that took me a few hours to port to 6809 have taken me a few minutes in C! Debugging with printf also tends to be quicker than setting breakpoints and watchpoints and inspecting memory dumps in the MESS debugger too!

The title and high score screens are there. I have the player running, swinging, climbing, falling & digging and the holes fill themselves in. The player can collect gold and progress to the next level. The demo runs too, but without the guards it doesn't get very far before the player is trapped. Deja vu.

Along the way I've attempted to implement an OS-dependent layer so that the core code should never have to be modified when porting to other platforms. Not surprisingly this entails the graphics, keyboard and sound routines.

I've probably got another week or two on this before it's finished. Aside from the mechanics of moving the guards, there's the guard AI on which I'll try to spend the most time crafting the C implementation. I'm hoping that this will serve to (better) document the core game implementation. I should also note that during the course of the C port, the purpose of both code & variables in a few places has become clearer; I'll have to go back and re-annotate the 6502 & 6809 code.

Once that's done I'll probably have a go at a Neo Geo implementation - or at least get the game running - before I get back to the final Coco3 release. At this point I'm not sure how I'm going to handle the bitwise collision-detection on that platform, but I'm sure I can conjure up something. A colleague has also thrown down the gauntlet, challenging me to get the circular wipe working on the Neo Geo. It won't be pretty, but I'll have a crack at it.

I'm also getting calls to resurrect my ill-fated arcade Tutankham port to the Coco3. The port consisted of patches to the original ROM image, which resulted in the game actually running on the Coco; you could coin up and play a game. Too bad the screen was rotated and there was no scrolling implemented. It's a tough call...

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