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Hard to say. I don't think anyone ever used those PLOT codes, ever, in the history of the Beeb

Interestingly, the AUG nails it.

Appendix E - Plot Number Summary

8-15 Last point in line omitted when 'inverted' plotting used

...which is exactly the implemented behaviour in OS 1.20.

Assuming, as you say, that the reason for providing it at all was so that chains of lines plotted in EOR mode would not have their joining points EOR'd away, the approach taken by OS 1.20 was quick and easy, and correct for its main use case, but not really correct overall. The change in the Master ...

Fairly sure my old school got rid of all its Beebs from the computer room and replaced them with RM Nimbuses around 1992 - I don't remember there being any Beebs when I did Computer Science A level around then. There were a couple of A3000s sat discreetly at the back of the room though, mostly used ...

Can't think of any examples like the Harry S Price Speccy ones though, where someone just ripped off entire pieces of others' games and passed them off as his own. I'm not even convinced Star Clash was guilty of stealing code from Elite. Always struck me as a double standard that Acornsoft brought a...

There were loads! Just Acornsoft alone came out with Snapper (Pacman), Planetoid (Defender), Meteors (Asteroids), Monsters (Space Panic) and Arcadians (Galaxians), Carousel (Carnival), Hopper (Frogger). Then there was Zalaga (Galaga), Deathstar (Sinistar), Skirmish (Joust), a bunch of Q-bert clones,...

I'm taking tentative steps into putting together a very simple demo along these lines - first step is a tool which can extract maps from Doom wads and convert them to a simpler portal format. (For the technically minded amongst you, this involves having to decompose an arbitrary polygon with holes i...

Come on this must be doable?! Surely hee hee. A little mockup screen....... :wink: :D https://i.imgur.com/4YlvQCh.png I have to say, that is very inspiring. And your eye for the technical as well as the aesthetic is superb (I noticed the exactly 128 pixel wide playing area!). When considering Doom ...

Incidentally this lack of bass tones on the Beeb is one of the reasons that a lot of music lacks so much depth on it. I worked around the limitation in the past by modulating a very high frequency tone on and off according to a VIA timer, but it's a shame to have to do that. And using periodic noise...

The lowest tone you can out of the SN chip at the speed it's clocked at on the Beeb is 122Hz, which corresponds roughly to the B an octave (and a bit) below middle C. So looking at that diagram in the User Guide, I would say Middle C actually does correspond to pitch 53 in the SOUND command.

Skirmish. Every time Skirmish.

Kevin Edwards wrote: ↑

Wed Feb 06, 2019 3:35 pm

How weird. I never noticed that before.

I wonder if it's because it uses 'offset' assembly and assembles the object code into sideways RAM. It looks like it's reading from the BASIC ROM?

Yep, I was going to suggest exactly the same thing

What I find interesting is that these values would also have to have been correct when Kev encrypted the game in the first place, so presumably you'd have to have the foresight to set those bytes up deliberately before encrypting, suggesting it was maybe intentional? I guess so, yeah. Those values ...

Ah look, this is the code I was alluding to (in JETMAN3 from Colin's disk image): 0C91 TSX 0C92 CPX #&FE 0C94 BCS &0CA3 0C96 LDA &0102,X 0C99 EOR &FE48 0C9C ORA #&01 0C9E STA &FE68 0CA1 BNE &CAD 0CA3 LDA &02,X ; <-- looks like it should've been LDA &0002,X instead 0CA5 EOR &FE49 0CA8 ORA #&01 0CAA S...

To answer your original question, someone certainly managed to get it on disk, as I got my hands on a hacked copy circulating back in the day. I don't know if it was the handiwork of Michael Archer (who goes by the name mikeybabes on this 'ere forum) who did Nightshade (and which US Gold subsequentl...

Here's a UEF image of the original tape (Alien8 is first, so you'll have to CHAIN"JETMAN" on an emulator and wait for it to skip all the way through Alien8 first, or use BeebEm where you can 'fast forward'). From what I remember of it, it's not dissimilar to Nightshade, although not identical either...

Oh... you guyz... Thanks for the kind comments! I actually may have some time to pick up some old Beeb stuff soon. But I know I'm terrible for abandoning projects and letting them rot once the interesting stuff is done. The Blurp video you linked to was the first demo with smooth scrolling, which un...

That's exactly the code I had in mind as a way to squeeze the rainbow owl logo into the OS ROM. I'm tempted to give it a go... If you decide to do this, remember to patch up the code around &CBC1 which sets the address within the unrolled loop! But beware - there are some games, e.g. Contraption, w...

My guess is that they wanted to make this as fast as possible to make MODE changes less ugly, but it doesn't really work as you still see the old screen for a couple of frames while it clears. By the Master OS, they abandoned the unrolled loop anyway, and it just does a straightforward top to bottom...

A lot of the Basic maths code is written unrolled, when it could be just as easily written as a loop. A quick browse of the disassembly shows floating point and integer addition and subtraction, floating point comparison, and scratch space clears and copies (among many others) to be routines which c...

Yeah, my take on this is that Repton was just a style of game which worked incredibly well on the Beeb hardware, given its hardware scrolling capabilities, which is probably also why there were a good few games of a similar style (Ravenskull, Pipeline, Clogger...). This style conversely didn't lend ...

you could fit the screen nicely in a sideways RAM bank (or indeed two, for double buffering), and keep all of main RAM free for code. Only the part of the screen where action happens need be double buffered, whilst the part of the games screen used for the score, lives etc. need only be single buff...

Always seemed to me that the Beeb's screen modes were unusually big. I once had the idea that, if you capped the max screen size to 16k (to give 25 line screen modes, which was pretty much the standard size on other 8-bit platforms), you could fit the screen nicely in a sideways RAM bank (or indeed ...

One way it could've been done is to put the code and data into the I/O memory mapped area and only activate it as I/O on the first data access. Would require hardware mods of course.

...and what sort of projects do you imagine you'd like to do with one? I'd like to find time to learn Rust, as it tickles my performance bone, and it might relieve some of my frustrations with the monster of a language that C++ is growing into. Also I really fancy getting to know a functional progra...

I treated myself to one of these recently, as it was on offer in Spain for Black Friday. I'm really happy with it so far - it's only a 15.6" screen, but it's 120Hz Full HD, and has some nice specs including 16Gb RAM, a 128Gb SSD + 1Tb HD, an i7-8750H processor and a GTX 1050 graphics card. All that ...

Looks lovely! Great to see such smooth horizontal scrolling on a Beeb. It's a shame that the background colours are reduced now (presumably the two bitplanes trick like Firetrack), but I wonder if there's scope to add some colour interrupts in there (as ridiculous as that sounds in MODE 2!), so, e.g...

The nice thing about Pacland is that the background graphics look extremely compressible! Looking on YouTube, the C64 looks very doable (it doesn't even look like it's scrolling at particularly fine amounts). The CPC version sucks! The arcade version has two layers of scrolling, so let's not bother ...

Indeed. On jsbeeb it's not a special case: we handle this by just performing the irq check before ticking the VIA prior to its read/write. In case you're wondering, here's what gets generated for LDA abs in jsbeeb: cpu.polltime(3); cpu.checkInt(); var addr = cpu.getw() | 0; cpu.polltimeAddr(1, addr...

Hey Chris, Great to have another pair of eyes looking critically over this stuff! Assuming this analysis is correct, it could explain the jarring discrepancy between row 6 and row 28 -- it seems suspicious that they'd behave differently. Yeah, I noticed that the results for rows 6 and 7 were likely ...