Learning by the book – part 4

Debunking The Machine Language Book of the Commodore 64 – part 4

I‘m going to try and attempt to explain and demonstrate the very daunting tasks of drawing lines (the whole basis of graphics)…

Your correspondent has, in over thirty years of working with 8- and indeed 16-bit home computers, drawn game and demo graphics for all of the Commodore 8-bits including the VDC display of the C128, the Atari 8-bit, Amstrad CPC, Sinclair Spectrum, BBC Micro, Apple II and a raft of other computers and consoles without using either the BASIC commands or an assembly language equivalent for line drawing to bitmap and, despite knowing a lot of 8-bit programmers and artists, has never spoken to one who claimed that line drawing was “the whole basis of graphics” on their chosen platform.

Even programs such as graphical text adventures where the user can watch the display being built from a series of lines which are then filled in are created either with bespoke solutions by the programmer which allow artists to create the images[1] or using pre-developed tools like the Graphic Adventure Creator or The Illustrator (which is the graphical extension of The Quill) where each image is stored as series of commands.

If drawing lines really was, as claimed by the author, “the whole basis of graphics” and the C64 lacks the BASIC commands to do that, how exactly does the author explain the truly vast quantities of C64 graphics? Your correspondent will leave the reader to mull that point over and we’ll move on to find out which other task the author feels is only “very daunting” on the C64 but not other platforms shall we?

…and playing polyphonic music on the C64, which is child‘s play on other contempory computers, such as the Sinclair ZX Spectrum (drawing lines, but only playing monophonic music)

In other words only one of the two tasks is “child’s play” in this case because polyphonic music on the Spectrum’s beeper requires assembly language and precise timing, which is significantly more daunting than doing the same task with the C64 from either BASIC or assembly language.

Acorn Electron (one channel sound only)

Again dear reader, only one of the two functions that are supposedly “childs play” can’t be done from BASIC and needs daunting, complex assembly language whilst the C64 in BASIC or assembly language would once more be easier. The same is true of the Apple II, some earlier models lack a BASIC command to draw lines and only have a beeper for sound unless an expansion card such as the Mockingboard; even when that’s installed there’s no BASIC support for it so writing to the card is done via POKE commands or through a music composition tool just like the C64.

Again as an aside, if creating music is so much easier on other platforms there’s a huge number of music composition tools around including the one that the author himself used when composing on the Yamaha CX5M.

We‘ll need to decide which 6502 opcodes to use in our line drawing programs. It‘s fairly obvious that they‘ll include LDA #number, LDA address, and STA address, as well as loops including the use of LDX #number, and LDA address,X but not clear what else.

Tying to tell other people how easy or otherwise a programming task is without actually understanding the programming language is utterly futile. And programmers don’t make the decision in advance about which instructions they use in the same way that writers don’t pick specific words from a dictionary before drafting a sentence, they instead have their entire vocabulary available.

It turns out that [the Bresenham line drawing algorithm] was developed as long ago as 1962, on an amazingly advanced for the time IBM computer called the IBM 1401, connected to a Calcomp plotter. I don‘t know if the computer could display graphics on a screen, but it could plot them on the Calcomp plotter.

So the author claims that the IBM 1401 was “amazingly advanced” but apparently hasn’t even done enough research to know what the machine potentially has in the way of hardware; this makes any comments the author makes untrustworthy.

Unfortunately, Bresenham‘s algorithm is a complicated algebraical formula. This means I can‘t understand it because I‘m useless at maths, so I‘ll have to design my own alrorithm, based on calculations as simple as possible, as well as tailor made for the C64 screen mapping where the graphics screens are divided into 40 x 25 character cells.

No dear reader, the sensible way to program this would be to develop an algorithm which works with X and Y co-ordinates and then translate the values it generates for the C64’s screen. This is how all the existing line drawing algorithms work on the various 8-bit systems so the author is trying to reinvent the wheel without even knowing if making it a square would be problematic.

I think the C64 graphics screen can be located at any one of FOUR locations in Assembly Language, so I think first of all I need to decide where to locate it.

It can be at six; those locations are $2000, $4000, $6000, $A000, $C000 and $E000 or if only the upper half of the screen needs to be bitmap (which is quite common for things like text adventures with graphics) it can be at $8000 as well. Using $E000 with the colour memory at $CC00 means the bitmap won’t take memory away from BASIC, but the ROMs will need to be disabled whilst writing to that memory which isn’t a problem since the routine is going to be in assembly language.

Perhaps I could find out whereabouts this point is on the screen, meaning in which character cell by dividing it, but I don‘t think there are any 6502 Assembly Language instructions which do division. […] All there seems to be are the instructions LSR meaning Logical Shift Right, and ROR, meaning Rotate Right, which are both ways of dividing by 2 each time they‘re carried out.

So after saying that he didn’t “think there are any 6502 Assembly Language instructions which do division” the author immediately goes on to recall your correspondent talking about LSR and ROR which are assembly language instructions which can divide by two. The author isn’t even trying it seems because he’s quite literally debunking his own claims before the end of the paragraph they’re in!

Don‘t forget that Commodore‘s own manuals were crap! It took lots of third parties, often from Germany, like the author of this book, to unveil the secrets of the C64!

Don’t forget that Commodore’s manuals weren’t trying to teach this very specific task that, as your correspondent has pointed out previously, isn’t actually essential to graphics creation despite the author’s claims.

As for my other learning activities, I‘ve been studying Japanese, as well as programming in Python.

These are of course irrelevant to the author’s stated topic of “explaining why the Commodore 64’s BASIC V2 was crap and how some people managed to program the C64” and your correspondent is actually getting tired of having to point that out almost endlessly but will continue to do so. This might actually be a form of masochism on your correspondent’s part, but after all these years it’s difficult to tell…

I have completed 75% of the Michel Thomas Method Japanese Foundation Course, so this proves that learning to speak Japanese is far easier than learning to program the Commodore 64.

The author still stupidly believes that his personal experience overrides that of everybody else; this is another example of the “I know best” attitude that annoyed the author when his father exhibited it, making the author a hypocrite for yet another time. If a single personal experience made any major difference to this discussion then your correspondent could simply point out that he failied GCSE French whilst successfully learning 6502 assembly language for the C64 because that would completely negate the author’s “argument”.[2]

[1] This process is documented in the Steven Levy book Hackers which describes the process used by Ken and Roberta Williams whilst developing one of the first graphical adventures called Mystery House. Essentially, Ken rewrote the software that came with a graphics tablet so that it could store what Roberta was drawing as a series of commands.

[2] No dear reader, your correspondent doesn’t have anywhere near the self image required to believe his experience to be of such ground-shaking importance, he instead leaves such arrogant, egotistical and false beliefs to the author.

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Guess who’s back, back again

Debunking Where have I been?

Theresa May kept me busy part of the time

That, dear reader, is something that should probably be kept between the author and Theresa May.

This blog isn’t actually about current events, although I do sometimes mention them to make my posts more interesting.

The author has presumably failed to process the sarcasm in your correspondent’s post; anything outside of the author’s stated topic is irrelevant because, as he notes, his “blog isn’t actually about current events”. It was very helpful of him to debunk his own post once more.

  1. I’ve been going to meetings, demos, and a march to try and stop Brexit.

That certainly seemed to go well dear reader, doesn’t it? [1] Let us skip gently over the remaining political discussion and get back to what the author is meant to be discussing but here’s a picture of Spitting Image by Domark because it’s tangentally about politics and actually related to the C64!

Spitting Image (C64)

Now back to the Commodore 64. Of course, not all dialects of BASIC apart from Commodore BASIC V2 supported hexadecimal numbers, but Locomotive BASIC on the Amstrad CPC range, as well as MSX BASIC did support them. Even Sinclair BASIC on the Sinclair ZX Spectrum supported binary numbers, but Commodore BASIC V2 and Atari BASIC only supported decimal.

So to recap dear reader, only the minority of BASIC dialects supported hexadecimal but the author only seems to perceive it as an “issue” worth noting with the C64; this is, obviously, hypocritical of him.

And this is hexadecimal we’re talking about as well,  the author has moaned at length about being “useless at maths” but rather magically that doesn’t extend to counting and carrying out calculations in base 16 it seems! Adding, subtracting or multiplying numbers (which is why the author whine that he “understand which one of these things it’s doing or why, because [he is] useless at maths” for what is essentially a simple equation if you pay enough attention to what it’s doing and actually try to understand) doesn’t get any easier just because the calculations take place in hex.

I remember reading lots of Commodore BASIC V2 listings which assigned variables to the locations of the VIC-II and SID chips, then used two digit offsets for the different registers. In spite of this, the impression I got was that there were a lot more memory locations I needed to learn than all the registers of these chips.

Which is a mistake on the author’s part because that isn’t the case. We’ve noted on countless occasions that he fails to do research and this is merely another example; he had no information whatsoever to back the assumptionthat there were more than merely a handful of locations to worry about but made the false assumption and gave up without looking further.

That assignment of variables with two digit offsets simplifies one of the author’s long-term bugbears, that he couldn’t remember five digit numbers – apparently he was aware of this in the 1980s but for some reason chose and continues to choose to ignore his own knowledge whilst complaining about it now, demonstrably trying to mislead his readers by doing so. And since the offsets are two digit numbers there can only be a hundred possible values, the author must have spectacularly failed to notice this when falsely getting the impression ” that there were a lot more memory locations [he] needed to learn”.

 There was also the weird command sequences working on these registers using the commands AND as well as OR, without any explanation from Commodore about why this was. It was explained in a magazine article I found a few years ago as “bitwise programming”, meaning setting certain bits in the VIC-II and SID chip registers.

It’s worth pausing to note dear readers that some BASIC dialects don’t have bitwise commands despite there being situations where they would have been incredibly useful such as reading the joystick on the Atari 8-bit for example, there’s a bespoke BASIC command but it returns a value where bits are set or clear depending on the state of the joystick so having the ability to AND by individual bits significantly reduces the number of condition tests required. And that’s before we remember that Atari BASIC uses POKE commands like the C64 to handle things such as the hardware sprites where bitwise commands would have been useful to deal with expansion registers, playfield priorities, collisions and so forth.

Of course this lack of functionality is overlooked by the author, either because he doesn’t want to poke holes in BASICs that he’s championing over the C64 or due to ignorance.

Assembly Language makes things much easier, with techniques such as meaningful labels in a pre prepared text file standing for memory locations, as well as those locations in hexadecimal being more memorable, such as $D000 which I posted some time ago could stand for display block, meaning where the VIC-II chip starts.

The author has yet to write any substantially sized program for a 6502-based computer so this is supposition rather than fact. Very few native assemblers have an equivalent of “pre prepared text file standing for memory locations” with some assembling directly to RAM rather than via disk. And the vast majority of assemblers both native and cross don’t require hexadecimal at all so C64 programmers who started with BASIC could carry the knowledge of decimal locations or indeed the concept of two digit offsets from a variable over to their assembler. Setting a label like v or perhaps vic to 53248 works in exactly the same manner as assigning it as $d000 for example.

And again dear reader, we’re talking about base 16 here which most people don’t count in naturally so decimal numbers would be easier to deal with at least for beginners.  There is a reasoanble argument for understanding binary since it helps when manipulating video registers on pretty much every platform we’ve discussed rather than just the C64, but only old hands like your correspondent who learnt assembly language via hand assembling and working in a machine code monitor needed to learn hexadecimal.

As for books about Machine Code/Assembly Language which aren’t dedicated to a particular computer, before you can actually do anything with them on a specific computer, first off all you have to read up on your memory map to find the screen memory, a routine to print text on the screen, etc.

And that is where a reference book comes in… like the Commodore 64 Programmer’s Reference Guide for example! This is, after all, what your correspondent has been saying for quite a while.

I’m now getting close to understanding the process of how other people managed to program the C64. In the near future, I hope to use Assembly Language to program lots of lines being drawn across the screen, then erased and replaced by some other lines, to produce simple animation, as well as to program a three channel polyphonic tune, without being dependent on specific software

The author really isn’t “understanding the process of how other people managed to program the C64” dear reader, there isn’t an actual process because different people have different motivations – not everybody has a childlike fixation with drawing lines for no practical purpose like the author does! Your correspondent learnt by setting himself achievable tasks related to the kind of games or demos he wanted to create and working out how to complete them, all that requires in the long term is a little persistence.

Other ideas of mine include a printed book based on this blog, as well as a graphic novel including my Dad with his “I know best” attitude (IKBA), the offices of “The A-Z of Personal Computers” with staff enjoying presents sent by Commodore in exchange for not mentioning that their BASIC was crap, etc. I may be setting up a crowd funder for these projects. There could even be separate crowd funders. One could be for people who want to see the book or graphic novel published, while the other could be for people who don’t want to see them published, such as the Tramiel family. Revenge is sweet!

Whilst publishing his libellous opinions and blatant lies under a pseudonym on his blog offers some degree of protection, it will be very interesting indeed to see how a print-based endeavour fares on that front since they tend to require real names and often contact details. How any of this equates to “revenge” is highly questionable, the Tramiel family will have legal options open to them to consider well before they think about essentially paying anybody off, assuming the author’s belief that anybody really cares about his writings is more than mere narcissism of course.[2]

And whilst nobody really fact checks the content of low traffic WordPress bash blogs (apart from people like your correspondent who do have better things to do with their lives but are often lacking when it comes to the mental fortitude to prioritise such matters) there’s a lot more scrutiny for published works, especially if they’re crowdfunded. The author is potentially going to draw far more attention to his lack of research, false assumptions and downright lies so how something like, for example, a negative review on Amazon will be dealth with should prove interesting; trying to tell a commenter on your blog that they’re wrong because you say so usually doesn’t go down well on its own, but if the feedback is from a paying customer it’s bad public relations.

Another thing your correspondent feels should receive emphasis is the author complaining about his father; since the entire premise of his blog and presumably the graphic novel would be the author knows best, the idea of berating other people for having pretty much the exact same attitude is just another demonstration of hypocrisy.

Not only that, but some more good news from the German “MagPi” is that the Raspberry Pi computer looks set to outsell the C64 in the near future, so then I’ll no longer have to listen to C64 fanatics crowing that their crappy computer was the largest selling “home computer” or whatever the term is.

No dear reader, the C64’s record is for the “highest-selling single computer model of all time” (the important words highlighted for the author’s benefit since he didn’t bother checking for himself) which means that every unit sold was to the same specification. Even if they’d matched the C64’s worldwide sales figures, 8-bit systems like the Sinclair Spectrum or Atari 8-bit line couldn’t hold that record because there’s a raft of different models; the Spectrum came in 16K, 48K and 128K flavours and the Atari 8-bit had even more models available with the original 400 and 800, the XL series, the XE machines and, because it has an optional keyboard, the XEGS.

The Raspberry Pi is in the same way a range of computers with different specifications rather than just one so the sales as a whole therefore don’t count towards the C64’s record because they’re not for a “single computer model”. Again, the author fails to do any actual research before posting and subsequently tries to mislead his readers…

[1] For the author’s benefit, since he struggles to recognise it, this is sarcasm.

[2] Anybody who keeps a blog is a narcissist to some degree, your correspondent included of course, but it’s one thing to believe that anybody would be interested in reading your thoughts and another to labour under the misunderstanding that a lot of people would pay for the same, especially when you’ve had a large amount of your “arguments” thoroughly debunked.

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Release Notes – WannaClone (Atari 8-bit)

Goodness dear reader, it’s been a very long time since the last C64CD demo release… hang on, haven’t we done this one before?! Well yes and no, because the Atari Age forum thread which inspired WannaClone for the C64 is the gift that keeps on giving, so now there’s an Atari 8-bit port as well! The music is brand new and supplied by Miker, conversion of the C64 version’s graphics was handled by José Pereira and your correspondent and a joke about the malware turning the user’s POKEY into a SID chip if they didn’t pay up was “borrowed” from Zapac in the forum thread.

WannaClone (Atari 8-bit)It’s worth noting that the Atari 8-bit’s processor is doing quite a lot of work during the picture, relying on a couple of cycle-accurate loops that change several colour registers per scanline, one of which is written to twice during each pass. This is more advanced programming would usually employ for a C64CD release, but your correspondent feels that the overall effect is worth it. The part of the code handling the decoding of text is identical to the C64 although the “magic number” used in the process has been changed from %6A to $A8 since the latter seemed appropriate.

Sadly 2600problems – the forum poster who inspired both the C64 version and this one by asking people to elaborate on encryption within the previously mentioned discussion thread – hasn’t acknowledged the existence of the C64 demo and probably won’t pay any attention to this Atari 8-bit conversion either.

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