| 18-Mar-08 |
Atari XL/XE Space Harrier Conversion Project
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16th May 2005
Cartridge Woes
In February I had decided to make the game into an XEGS format cartridge, for lots of good and sound reasons - but I hit an unexpected problem; my code just wouldn't work. Normally, you eventually figure out the stupid thing that you're doing wrong - but this time I couldn't, so after trying some simple test cases which also didn't work, I figured it must be the Atari emulator that was broken! The switchable XEGS cartridge emulation in the Atari800 based emulators would not switch back on after it had been turned off - The cartridge normally maps over the top of a sizeable chunk of RAM, and you need to be able to switch it on and off in your program to get at that RAM and the cartridge data. I reported the problem and figured it would take ages before it got fixed, so I changed everything back to using the MegaCart format. Like carrying an umbrella ensures it never rains, this was a sure fire way of getting it fixed quickly of course, and by the end of the week it took to change everything back, it'd already been fixed. Even Atari800WinPLus version 4, which is my favourite emulator, and which had been stuck on Beta 3 for nearly a year, got updated to...Beta 4. But well done to the Atari800 and Atari800WinPLus teams for such a quick fix. I'm in no hurry to change things back yet again, so it can stay as a MegaCart for the time being.
Reset Bug
To my horror, I noticed that the Reset key was occasionally failing to restart the cartridge correctly. Since I had spent a lot of time about a year ago figuring out how to trap the Reset key under all circumstances, it was a bitter disappointment. Since everything else appeared to be working beautifully, I just couldn't believe it. I had to go back to the builds from that time to try and figure out what was going on. The good news was that I hadn't deceived myself that it was working when it wasn't; the Reset trapping was working back then. It was a mammoth task, but eventually the offender was tracked down by going through my change log and gradually undoing the changes that looked like they might be relevant. Turned out to be a not very obvious timing problem, so I am just glad that I kept track of every change that was made, and had kept all the source and build versions - Or I might have still been scratching my head now.
Minor Problems Fixed
Finally got around to fixing screen glitches on the start of a new game with a remarkably simple piece of code - The screen only gets switched on during Vertical Blank.
Changed the score line to be 8 pixels high (Antic Mode 2) rather than 10 pixels high (Antic mode 3), as it will cause fewer problems with making the top grid descend for Stages 4, 9 and 14. Downside is, the outlining of the words "top" and "score" is not so obvious now.
Changed position of numeric characters in the character set to make checking for the top score easier - because of leading blanks instead of zeros in front of the score, makes sense for the blank character to be an earlier character in the character set than the numbers.
I don't know if anyone noticed this on the Demo version, but alien missiles don't start exactly at the position of the alien that fired them - they only show up on the next step of the way down the line to the front of the screen. On some fast moving aliens, they could actually look quite disconnected from the alien that fired them. It'd probably be no big deal if it stayed like that, but it looks a little better now.
Busy time with the alien missiles - Also fixed a problem where they would hang around too long at the front of the screen if fired when the alien was close to the front of the screen - Reworked the way the speed vectors get calculated.
Stage 3 Revisited
Nearly all the graphics have been redrawn for Stage 3, to take advantage of having enough memory with the cartridge for more colours per object, and this has taken some while. Stage 3 is one of the prettiest in the game, and I've been trying to do it some justice on the little Atari.
