Enemies!
Thursday, 8th September 2005
They claim a picture says a thousand words.
In this case, with these two pictures and one video [549 frames] I estimate that I have saved myself from having to write over half a million words in this journal entry.
There is, of course, the usual shonkily shot video footage to watch: 416KB AVI.
The collision rectangles need a little bit of fine-tuning and something better than just vanishing sprites needs to be implemented, but the modular and simple system is there.
Each level contains a pointer to an "attacks" table.
Each "attacks" table entry contains a $FF terminated list of attack patterns, in order.
Each attack pattern specifies -
- Which sprite number to use.
- A pointer to the routine to call to initialise the enemy sprite locations.
- A pointer to the routine to call to move each enemy sprite each frame.
- An attack time.
Each enemy is held in a table containing an X,Y coordinate and a "ticks" counter that is incremented each frame automatically.
The "attack time" timer is primed and decremented each frame, and once it hits zero the system moves to the next attack pattern from the level's list.
This means that I can have a number of different patterns. So far, I've implemented a simple sine-wave attack and an even simpler random-positions-and-drift-past attack (both from the original game), but some attacks are more complex, relating to paths or drifting towards the player. This system I have in place should make having a wide variety of different types of attack simple.
I got so far, compiled, ran on my Game Gear and - oh dear. Lots of nasty name table corruption. To save space, I had decided to check the bullets against the enemy ships inside the sprite-writing routine, which was obviously too slow (much popping, pushing and use of the index registers) and as such the sprites were being written after the screen had started to be displayed. I have moved the code outside the loop and restructured parts of the code, but I hope that I have enough time/space to implement other things properly, without being restricted too badly by the low CPU speed.
I'm not getting far with this elsewhere, so I'll ask here - anybody here with BBC Micro skills?
I really need help with the music side of things - not so much writing a sound/music engine for the game, but more the actual "porting". The BBC Micro has the EXACT SAME PSG in it, so I could probably write a modification for a BBC emulator (BeebEm, for example, comes with source) which logged writes to the PSG hardware port (and time-since-start-of-program), but I'd still have the piou-piou-piou-skrrch sound effects over the top. Does anyone have a BBC Micro disk with a copy of the Fire Track music on it? I remember seeing/using music collection disks which featured game music on them a decade ago, and SOMEONE must have a "raw" copy of the Fire Track music (how else is there a recording in the STH archives?) but nobody on the STH fora seem to be able to or want to help.
Finished the levels! Wahey!
Wednesday, 7th September 2005
...and here is level 6. This, however, worries me:
Hopefully I can cram in all the rest of the code, tables, graphics and music into 5K. Failing that, I might have to start compressing my levels...
I don't believe I've introduced you to my enemies yet? Here's the complete sprite table - don't worry, the letters P, A, U, S, E and D do not feature as enemy craft!
I spent some time adding a new command systen to QuadPlayer, so you can now set a song to loop back X times (or infinitely) to a particular spot. It'll only loop from the end, sadly. Nested repeats will be too evil to try and implement. I'd like to experiment more with white noise - maybe a command to set up certain channels as being white noise rather than tones? Not sure how I'd generate the white noise, as the register R (which is the source of my random number generators) isn't going to be very random if accessed in a short loop!
Sample song, from a Kirby game (I added the fade at the end manually, that's not produced by the calculator!) Not bad, seeing as it has been generated by a calculator with no proper sound hardware. 
ASCII Madness II and Tutorials
Friday, 5th August 2005
Well, it's been a long time - here are two updates in one!
First up, ASCII Madness II. It's a text-mode scene demo that runs in the Windows console using characters from the extended ASCII set to produce the effects.
You can download it (and the source) from here.
Next up are some simple tutorials. Oldschool graphics stuff, I'm afraid, but hopefully someone will find them of interest. They are presented in the form that I would have liked to have read... and I know that I'm not very conventional in my learning style.
I'd be interested to see if the demo apps (blobs, tunnel) work fine - I've had one complaint that they can't find a particular DLL, which is a bit odd.
QuadPlayer - four channel sound from a TI-83 Plus
Monday, 18th April 2005
No longer are we limited to two channels of sound, but here we have access to four!
If you have a TI-83 Plus calculator, there's a preliminary release here - and if you don't, some zipped up MP3 recordings here.
Z80 ASM and PICAXE
Wednesday, 13th April 2005
I've been doing all sorts of odds and ends recently. I've acquired a Sega Game Gear, and so have started taking a look at programming on that - it has a Z80 CPU in there, so the languge isn't an issue, more so the hardware. Ah well, I can display a screen of text and cycle the colours around so far - nothing impressive, but the setup works.
I've also been playing with PICAXE microcontrollers again. Here is a pair of routines that can be used to get/send bytes using the TI hardware link protocol, for example. I am yet to do anything useful with them, however.
Windows programming has never been my favourite side of things, but I have also started work on a Z80 ASM "IDE" called Latenite:
It's mostly there, but now needs features galore to be added. So far it can be used to compile and source code, which is the main thing.