Playing Acornsoft Planetoid in 2017 compared to 1995-1996

On this page:

See also, on separate pages:

defender, what planetoid emulates, mostly acornsoft planetoid and defender
acornsoft defender instructions acornsoft planetoid instructions
Note that the score for a bomber is actually 200 points, not 150 as per the instructions...


In April 2017, having some more time to spend on hobbies I decided to play some games on my BBC micro. I saw's high score competiton tried the current game, Galactic firebird. I got to 27K or so, and others had scored 33k+, but I didn't want to try further as the game just didn't grab me and what I really disliked is the too long pause between dying and playing again, but still I wondered if my skills were now rubbish or that I just needed a bit more practice on that game. Well, to compare then and now, I tried one of my favourites, Planetoid. I could have tried Fortress, at which I got to 268000 and 248000 in 1986, but I am sure that those scores are almost impossible to improve on as I played perfectly for the highest score. I had to even shoot a few barrels of fuel that are hard to get to (behind walls), and for a higher score I would need to shoot a few of the barrels that are almost impossible to get to (also behind walls but closer to them and/or with enemy planes, not sure) because fuel depletes faster each time you go through the course. So Planetoid it was, after not having played it for almost 21 years. My high score in April 1996 was 888150, what would I get to now?

First 3 days:

Tried Galactic Firebird again and got to 33850 which was OK but not great, but I couldn't get myself to put in more effort. So back to Planetoid.

Over the next weeks I played Planetoid from time to time, with my score getting higher, and the realisation of how much high scores depend on subtleties grew (how to not get killed in certain situations, and to make effort to not kill your last man, and in general how to deal with certain situations). It just takes time to master them and to apply them. Also you hit a almost-wall until you get to wave 32, you need to become good enough to reach that (you will get there with about 520k points) and of course have enough lives and smart bombs left over to continue, as at this point the shoot-speed of aliens wraps around making it manageable again, and you can continue. It doesn't get easy as the aliens become faster all the time and suicidally run into you! The swarmers' speed is a problem at high scores and even worse are the baiters/cruisers. Comparing my scores with those from 1995-1996 (I wrote down all my high score improvements with dates) showed that I progress much faster than then, and I felt that I could definitely improve on my 888150 high score. At the time I felt more than 900k was possible and I wanted to get 1M+, but it was frustrating when the speed of a lander is so high that they take the last man up a very long way in short time and if you get killed often a lander still got to the top resulting in a mutant fest if it was the last man. Also, other things took my time from mid 1996 on. Well, I will try it this year... Shoot speed should, at a bit more than 1M, reach the maximum again so it will be difficult.

I made some videos, first with S5, then with S2 which is a bit blurry for some reason (in short tests recording Planetoid the video was better than of the S5 in low resolution)


In a bit of night play on 6-7 June 2017 I got 2 improvements for 2017: 812450 and 857300 (end of wave 50, the maximum tab bombs/lives I got to was 39/28). The large number of tab bombs meant a good buffer for situations such as not keeping the last man alive, as happened twice in the 857k game, in wave 47 most notably so a bit more than 2 waves in a mutant fest. I also wasted a few smart bombs accidentally pressing TAB twice (first time that ever happened to me during playing Planetoid, curiously). The score is very close to my 1996 high score, so my skills are definitely not worse than in 1996. I know for sure now that I can improve on my 1996 high score by a large margin because in both 800k+ games I was testing tactics and not playing optimally at all.

A while ago for a high score competition I also briefly tried Zalaga for several games and within a short time I got to just under 150k, whereas in 1995/1996 my high score was 154k. So, very close but I didn't try to improve on it as it is such a boring repetitive game, and I know I felt the same in 1996, which means that I didn't do much effort for a high score then, just as I didn't do much effort this year, and thus any comparison would likely not tell anything about the ability to play computer games now vs. then... (that fact was a big part of the reason why I didn't continue to play this game further to get a higher score in that competition)

2017-7-24: I think I can score 1M+ with the current strategy, but I have been analysing what I need to do to score much higher which would likely be needed if those scores of 2.8M and 3.1M are real. I've tested a new strategy with short play-testing (up to say waves 10-15), so far not succesful. If I get no result soon then I will go for 1M+ with the old strategy. Or devise a new strategy... [ Addition Nov. 2017: From testing with high wave numbers, the 2.8 M and 3.1 M scores are not real, or at least not made on a BBC micro with the BBC micro version of Planetoid ]

2017-10-21: Some practicing with different tactics, and no highscore from that but see my tactics page for more on that. I did improve my 2017 high score to 873,600 on 21 Oct. I would have improved my all time score if it was not for killing the last man at wave 50! (and before that at wave 30...) Aargh!

2017-11-12: I played a game, almost wanted to quit as after losing the first life at an OK score, the next 2 were too soon, but I continued. I got into a rhythm, experimented as I did a while ago with letting landers at higher waves pick up men too. I got to the highest number of lives smart bombs ever, by a large margin: 36l / 44b or even 37/44. Later I wasted a lot of it at wave 45 and 50 by again shooting the last man... I got to wave 53 with a score of 941,950, so, a higher average score per wave than in 1996. So my old score is history, cool. From how this game went I can definitely do 1.1-1.2 million (so, close to my initial rough estimate of the maximum achievable score). I got the hang of dealing with baiters at almost all levels. That's why I had so many smart bombs. The swarmers are still a problem.

Comparison with Alligata's Guardian, the original Williams Defender arcade game and a few more BBC micro versions

Acornsoft Planetoid: This game gets harder all the time, but at wave 32 one part of the game gets back to easy. Why wave 32? Well, think about 8 bit values... At this point a wrap-around occurs of shooting speed, bullets are nearly motionless (and so you can deduce that likely 8 gets added to the bullet speed each wave and that the start speed was about 8, or 7 gets added each wave and start speed was ca. 39, or, with an addition of 6 each wave start value was 64, etc. I will check my disassembly to see which it is, though from playing it doesn't feel at all as if shot speed gets doubled after wave 1 so likely it's the 2nd or 3rd (Seems actually to be 8 from what I wrote down in 1996 but I will check further as it must be a limit rather than actual speed as in wave 2 speed is not doubled from wave 1); There is some variation in shot speed but mostly up-down (more on this will come in the tactics section). So when you get to wave 32 you've got a reprieve from the unmanageable speed at which aliens shoot at you at around wave 28-31 (it already gets quite hard from ca. wave 25), but the movement of aliens still gets faster all the time and they don't care about colliding with you, thus killing you! Baiters at I would estimate around 800k points have a wrap-around in move-speed, and you can easily shoot them again... Although never really easy as they are so thin. This is a very rough estimate as I tend to avoid them appearing/analysing them at the lower waves as mostly they just kill me ;) In general hitting aliens is a lot harder in Planetoid than in Guardian and Williams Defender. Mutants at 800k+ are almost unmanageable, because they are so fast... (landers too but these are manageable as they are not homing in on you). When will the speed of landers and mutants wrap around to near 0? I should examine my disassembly... Oct/Nov. 2017: I found my disassembly again which includes a near complete analysis of all workspace and variables, and from that it is clear that mutants and landers have no wrap around speed as their speed is determined by the sprite update number. Baiters are manageable at high scores because the adjustment of their speed to move towards you is shifted so much that it reduces to 0 (overflow and all bits are gone) and stays still. Amusing effect that I noticed at 800k+ already when playing. Landers and mutants at e.g. waves 100+ are just too fast to deal with. See the high score page.

Acornsoft Defender: There is an earlier version of Acornsoft's Planetoid called "Defender", which I was told long ago has some bugs. From a websearch I reached a video on youtube where I saw a comment that if you end the wave with 10 men lifted, then the next wave you will end up with 256 men and no aliens. This sounds fishy of course, as the number of men is likely stored in a byte so you would never get 256 of them. And when I tested to see if anything interesting happens: Nothing interesting happens, the next wave continues normally. So what are the actual bugs? I will try to play this early version more in July or August when I return from a long trip and then I suppose I will find the bugs... Update: Delayed, possibly October or November I will try this. Or I may do a diff of the binaries.

Other versions of Acornsoft Defender/Planetoid: There are a few modified versions which are not offical releases, such as "Modified Defender" and "Super Defender". I prefer Planetoid, I mentioned one issue above, I will try them again soon and give my more verbose verdict...
2017-10-29: With my disassembly from 1996 of Planetoid I found a brief analysis of the differences in the binaries Planetoid and Super defender: Super defender has been made easier... More to come.

Alligata's Guardian: Interestingly the intro screen says 'Defender' :) Another oddity is that the prefilled top score table says "top ten session scores" but in fact there are only 8 places! This game is more accurate in emulating the Arcade game, well, at least in movement patterns of the bombers, baiters and swarmers, than Planetoid. What is bad is the lack of colours. This makes it harder to play, esp. the radar is hard to read. Also bad is the very poor sound. The game looks to use a single sound channel for use on the Acorn Electron, which means a new sound cuts off an already playing one. This game seems to have been released only for the Electron which makes sense as anyone with a BBC micro would likely have Planetoid already. Those are 2 of the reasons why I don't like Guardian, but there is more such as the too long continuing of motion (too slow deceleration) and the too long lifetime of bullets, which makes reversal to make them go off-screen (= gone) and then back, almost a necessity for playing, all the time, instead of as in Planetoid, a method to be used most of all in extreme situations. Another issue is that there are too many landers appearing at a time (8 instead of 5) which makes it a quite different game to play. With Guardian you need to hammer the RETURN key all the time to kill all of them off (before the baiters arrive). In this game bombers and baiters behave more like in the arcade game, with random up/down direction changes of the bombers, and the baiters moving rather less predictably than in Planetoid. This takes getting used to, you need a different approach. Shooting aliens is rather easier in Guardian, often with the bombers in Planetoid for example, hits don't register, in Planetoid collision detection is colour based rather than sprite shape based, I think. This shows also in the modified version that is around called "Super defender", where landers are very hard to kill because of this... I've not played Guardian long enough to see a wrap-around in shoot speed or alien movement speed (as happens in Planetoid at high levels), I played it only long enough to beat the highest score that I saw on and got to 389050, it seemed to get faster all the time, what will happen in higher waves? Update 2017-10-13: I hadn't played any games for about 2 months, so tried a few games of Guardian to see if it my ability to play such games was affected by not playing a few months. With Planetoid it's harder as each game takes quite a long time, so to test I tried Guardian and I got immediately to a few scores around the 370k mark, then another game where I felt I was in a rhythm and got to 471,150. I think I can score a lot more but it would mean more playing to get more accustomed to flying patterns and responses that mean evading bullets instead of flying into them quite a bit... I didn't feel the game was getting that hard but there was no speed wrap around of anything as far as I noticed.

Micro power's Gauntlet: I played it only briefly, it is almost but not quite Defender, with different shapes of aliens, different scoring and the bombers fire bstards at you ;) I could describe it better but I'd need to play it more and just playing it briefly I just don't like it, it's like playing in molasses. I think it's caused by the low speed and almost instant deceleration. Speed and deceleration are perfect in Planetoid. In Guardian deceleration is too slow.

Willams Defender (the original arcade game): I read somewhere that this is normally limited to a difficulty that stays at that of wave 15, so if you master the game at that level, then you can go on forever... (that explains people looping it and that with endurance play people get to near 80 million points) Movement of bombers and baiters is very different in Planetoid than in Defender, and baiters appear a lot more quickly with less than 4 aliens remaining. I only played Defender briefly when "Williams arcade classics" came out, I think 1996? Maybe I will try it a bit more this year (using MAME).

Planetoid: Practicing

1. Play using only the radar: Put a piece of cardboard over the main part of the screen and play using only the radar to make you use it more. The radar is more important than the screen because you need to keep an eye out for all men that get picked up so you can rescue them (and get points) and at higher levels to keep an eye out for your last man.

2. Shoot all men and then don't use smart bombs: This is to practice how to handle the mutants. You can do this at wave 1 but doesn't really matter when you start.

Possibly useful for practice?

I've not tried the following as I feel that there's no real need for me, but it could be useful anyway or at least interesting:

3. Play with the radar covered up: If you rely too much on the radar and get shot by aliens on screen while watching the radar too much, this could be useful as in normal play you need to balance looking at the radar and the main screen. It could actually be more interestingly used as a way to make the game harder, for competitions for example.

4. Play without using smart bombs: I don't use smart bombs until I get to about 300k points, saving them for situations at higher levels... Not using them at all will give good practice to handle various situations at higher levels when you want to conserve some smart bombs. For me it's probably not needed as I only use smart bombs when I feel there is no other option (i.e. to get rid of a bunch on bombers and pods/swarmers which at higher levels go so fast that you need to remove a bunch of them so you can handle the rest (if any are left). Again this is likely more interesting as a way to make the game harder for competitions.

Planetoid disassembly and patch

I found my disassembly from 1996 with complete list of all variables used etc. Also included is a patch with fixes for a few issues that I describe further on. Using the disassembly I changed the score to 4 bytes (for in case I go beyond 1M, for videos if the score is displayed as 8 digits in-game (which I don't do for now), and for screenshots of the high-score display).

I finished the 4 byte score patch combined with the patch from 1996 on 22-10. Then on 25-10 and 27-10 I made a few small changes in the pause/continue and escape code. The current patch is v03 which fixes and upgrades the following:

Code to come (t.whsp03 / b.whsp03):
(1) Rename the file PLANET2 from Planetoid as O.PLANET2.
(2) Use the Basic file or *EXEC the text file, press Escape. You can select what you want to use or don't want to use by letting the PROCs execute, or by commenting them out. So modify the code if needed. SAVE the file as "B.whsp03" or do the modification when the file is loaded at &4000 as then the file won't reload itself.
(3) RUN. This saves the modified PLANET2 file. Now CHAIN "PLANET" will run the modified Planetoid. The patch version is shown at the bottom of the MODE 7 score screen.

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