Quake on an oscilloscope | Hacker News Reader

Quake on an oscilloscope

lofibucket.com

859 pointsmarkmassie70 comments

This was how we did computer graphics before there were affordable (less than $50K) frame buffers in 1980. In my 1975 MIT Digital Systems Lab my team constructed a hardware Game Of Life out of TTL gates. I designed the display as timed X-Y points on an oscilloscope. In those days a kilobyte of RAM still cost a hundred dollars, so the computer lab rationed the number of memory chips each team could use. I recall we stored the automata in a dual 64 x 64 bit frame buffer or two kilobytes overall.

The first generation computer graphics languages were vector-oriented to support either oscilloscopes or pen-plotters.

My first color frame buffer terminal was 512 x 512 x 8bits $30K AED in 1980. I think this costs than a dollar on a low-end cellphone now.

Ancient desktop is todays (or at least yesterdays) embedded. I guess this dates me but instead of taking the legacy Z80 embedded micro controller class a long time ago, I took the then new brand new 68hc11 class, although the Z80 guys got to use two DACs and a scope to display a cube on the scope as one of their labs. Now using a mhz class cpu to output a table at khz speeds isn't very impressive, so logically the next step in the lab was rotating the cube. I donno if they had to dream up their own trig or got a canned library. Maybe they canned the whole thing and just stored 30 or so frames of rotation data and switched which frame they displayed every tenth of a second or whatever. Donno didn't take the class but we got to see their work on lab day.

I would imagine whatever took a "sheet of paper" sized development board with dedicated hardware DACs and eproms around 1990 could be done as a single chip solution today, assuming you can find a single chip solution that actually has two on board DACs. Or up the challenge by synthesizing PWM signals and low pass filtering them, essentially a class D amplifier controlled by software.

That sounds awesome.

Surprisingly or not, PWM circuits (a counter and binary comparator) are more common than DACs on today's microcontrollers. I blew up some somewhat expensive tweeters finding out that just because you can't hear the 31.275kHz PWM carrier doesn't mean the amplifier isn't amplifying it.

It is definitely plausible that they were rendering their spinning cube in real-time. A lot of people have written wolf3d-style raycasting engines for z80 (mostly z80-based TI graphing calculators, which are clocked between 6MHz and 15MHz. much faster than a TRS-80 to be fair). This guy even made a doom-style engine: http://benryves.com/journal/3739423 (see animated screenshot). The stuff the demoscene has done with z80 microcomputers can be even more impressive.

True, but I was concerned with it being a school lab, they were already demonstrating dual dacs, linked list data structure with semi-complicated data structure (well, OK, x and y values and maybe just a dumb lookup table) in assembly. Asking them to add a third aspect of trig might have been too much for one lab so maybe they canned the rotation and just had a very large data table animation rather than calculate on the fly.

My project for the demo day in 68hc11 class was the 68hc11 was a weirdo among microcontrollers for having an external memory bus, so I slapped a 32k sram onto it making it a 32K MC and made what amounts to a drum sampler, press this button to record a couple seconds off the onboard A/D and press this button to play it back using an offboard DAC. Now a days of course microcontrollers rarely expose their memory bus and you'd just buy a COTS MC with more memory on the chip. We only had one day to prep for demo day and asking the Z80 kids to do DACs, and a vector algo, and trig all in one day might have been asking too much.

Its been awhile, but I think the demo day theme was we all had to use at least one off chip DAC.

I saw a video titler which solved the problem of expensive memory by keeping the frame buffer compressed, and decompressing it at frame rate. I remember that composing the image was very slow (on a 4 MHz 68000). The compression algorithm was run length limited.

The product was the Vidstar-2000 from Video Data Systems in 1984.

Some early flight sims used a trick of rendering just before electron gun beam. You only needed a small amount of ram for a big screen, as long as you were able to keep up with the beam.

I'm old enough to remember when my college computer lab had an analog display for one of its systems...if I remember right, it was used for LaTeX applications and development, which during those days was still an interesting CS direction.

I used to be mesmerized by it..everything looked so clean and modern, much better then the crappy 80x25 "workstation" displays of the VAX's and PDP-11's.

...a vector display.

This doesn't make sense in my head: I don't think vector displays were ever used for type setting, but I would love to be proven wrong. Do you have anymore information?

Well...maybe not LaTex, but some sort of mindblowing text to my CS101 mind.

What I remembered was this device... https://en.wikipedia.org/wiki/Tektronix_4010

The 4014 had a series of commands for drawing both text and graphics

I was at the Florida Institute of Technology in 1985, and Lamport had just published the LaTex language and their was some interest in the department in getting a version of it running the the 4014...

I think someone hacked a version of it...but my aging memory fails me.

Vector displays don't usually handle text very well. They can draw perfect curves, but I don't think they could ever do the Bezier curves that fonts depend on.

Anyways, what you are referring to is in between vector and rasterized displays. Still very interesting. I should ask my dad about this (he worked for Textronix in the 70s).

>This means the frequencies emitted are very high (5 samples per period is 19.2 kHz) and it seems the audio output is being low pass filtered resulting in silly wobbly lines.

That effect actually looks amazing. I'd totally play a game with that aesthetic.

Would it be possible to recreate that effect on a raster display with a shader?

It might get a bit complicated but sure, there's no reason you couldn't.

Part of it would be done on a shader (mainly the visual portion, like the glowing and whatnot) but I think most of the effect would need to be done on the CPU.

You might be able to make it work with clever usage of geometry or tesselation shaders though, and maybe also transform feedback.

Honestly though, since the effect necessitates simple, low-poly geometry, doing the effect on the CPU shouldn't be too unreasonable, and would be where I would start.

EDIT: Actually, now that I look closer, the one on the right here[0] could be done more reasonably in a shader, I was thinking closer to the one on the left (and how it actually looks in the video).

[0]: hhttp://www.lofibucket.com/articles/img/speed_comparison.jpg

Always fascinated to see people use alternate input methods. I wonder if there is some possibility for steganographic applications with this? I.E., plug a soundcard into an oscilliscope, play a specially crafted .wav or equivalent file, and viola, secret message?

Something similar has been done on wavs e.g. when Aphex Twin hid his own face iniside the windowlicker track: http://www.bastwood.com/?page_id=10

Plaid did this too on "In Threes." It's really fun to mess around with.

I once wrote a program doing something similar: https://github.com/kgabis/spectrum-printer

Here's a music track which is its own music video when played on a 2D oscilloscope:

https://www.youtube.com/watch?v=GvX5UWnUYTc

clicking around after this video i came across this: https://www.youtube.com/watch?v=YqSvkNjWnnQ

wow that looks and sounds amazing.

Hypnotic. I wonder how the artist designed the visuals - is it only by math?

He used framework called Pure Data to build the sounds by additive synthesis (of pure sine waves). If you do that with some care (and you can pick the phases of the sine waves freely), you can build/explore/craft some pretty funky visuals quite easily, I imagine. It's the large scale composition, making it into a coherent whole that seems hardest to me (then, that is always my weak point when making music, I'll just keep practising :) )

Didn't Woz have the original Apple computer outputting letters to an oscilloscope before he made the circuits to output to a television?

Lots of older systems had vector rather than raster displays, from what I've heard of people who used them (too young myself) they were highly interactive - you could design movement and animation much more easily, and make the display very responsive. The major downside was not being able to do colour (easily), and not being able to cope with a lot of on-screen complexity (like the line count here not being much to shout about). Rasterised displays are a special case of vector, but with fixed bandwidth requirement.

There was a game console for vector games, named Vectrex.

The games that ran on it were really interesting.

Many modern games use the now high-resolution of raster displays to imitate Vectrex-style graphics.

http://www.binaryzoo.com/games/echoesplus/echoesplus_4.png

Note that the corners between straight lines are brighter, it is because on Vectrex the way to control line brightness was to draw it over itself, also line crossings were brighter too.

Important to mention that many vector displays could NOT make curved lines though.

One of my favorite vector games was Tempest.

Vector graphics were some of my favorite, even growing up during the NES/Sega era.

Several of the famous commercial arcade cabinets were vector too, including Asteroids, Battlezone and (as tomswartz07 mentioned) Tempest.

Don't forget the original Star Wars cabinet!

http://www.i-mockery.com/minimocks/50arcadecabinets/star-war...

Of possible interest to HN readers is that the system and all the official games are public domain:

http://www.gamasutra.com/view/feature/3117/a_history_of_gami...

"After product rights reverted back to Smith Engineering, an attempt was made in the late 1980s to resurrect the Vectrex as a handheld. Unfortunately, the pending introduction of Nintendo's GameBoy in 1989 put a practical stop to such plans once and for all.

In the mid-1990s, Jay Smith generously placed the entire Vectrex product line into the public domain, opening up legal, not-for-profit distribution."

Consequently, it's well supported by emulators.

There was an early home gaming system called the Vectrex that was based entirely around this. They got around the lack of color with clear plastic screen overlays.

https://www.youtube.com/watch?v=ijc6afTifqI

We had one when I was growing up as a kid. It was a pretty cool little machine.

I don't know about Apple, but Tektronix made both terminals and microcomputers with vector graphics.

This would be a very cheap way of representing cyberspace in a b-movie. It already looks massively better than the Matrix's falling green thingies.

That looks really trippy. I think it would actually be a cool rendering mode to have in FPS games in general, on computer screens, particularly the cyber-/techno-punk kinds.

At first, I thought this was just going to be another person discovering that analog TV sets were really just oscilloscopes with predetermined sync; and then setting up a sync for the scope to turn it into a little TV...

How nice to be wrong! Hats off on this one. Nice hack indeed.

I wonder if the limit on lines was due to 20 kHz filters on the audio output. When the 24/96 audio sampling & perception discussion went by a few weeks ago I seem to recall some testing showing that even high sample rate sound hardware had low pass filters just above 20 kHz. This kind of issue should have been easy to spot in development and testing, though, so maybe just a limitation of the medium.

I've got an old hobbyist oscilloscope, it was my former boss and mentor's first scope. I really should hack up something with it along with some of these low cost cpu boards.

Wow, great!

I can only try to imagine how it would look on a oscilloscope with more MHz and a better soundcard.

Given that this is a realtime 3d space squished into the bandwidth of audio, could a variation be done with a worn kinect to feed into headphones an audio waveform version of current surroundings that is capable of being translated by the brain back into 3d. As that sounds like a possible hack for giving some form of vision to the blind.

I'm not so sure. The brain's ability to process and interpret visual information and form an intricate understanding of 3d space seems to me a "hard-wired" process.

Sure, you could convert information encoding 3d space around a user and convey it to them in any number of methods, but that wouldn't leverage the brains very specialized mechanism for processing and interpreting visual information(which I rightly or wrongly conceptualize as a mix of hardware(some analogue of a video coprocessor for the brain) and software(the algorithms the brain uses to interpret the data).

Examples such as Daniel Kish suggest otherwise -

http://en.wikipedia.org/wiki/Daniel_Kish

https://www.youtube.com/watch?v=ob-P2a6Mrjs

The first link is interesting, it does say the saw signs of activity in the same brain region of a blind echo-locating person as a sighted person who is activity looking at something, but it is hardly a smoking gun.

Perhaps if you are defining "3d" information as something very primitive to the point of being "is there something directly in front of me", but nothing even as close as rich as even the quite crude 3d information being conveyed on the hacked oscilloscope outlined by the OP.

I do see technology eventually giving blind people some sort of "sight" back, but not for quite some time, perhaps after there is some sort of workable neural interface that currently lives solely in sci-fi.

Regarding the sound card, from the description it looks like the "crappy" sound card also employs a high-pass filter.

Is there a reason for it? What kind of circuit design in the DAC could cause low frequencies/significant distortion to require a high-pass at these frequency ranges?

Genuine curiosity here.

It's a low pass filter. And I'm assuming the low-pass is used in the DAC to cut off high frequencies it cannot handle.

What frequency ranges do you mean? Digitally, you can feed the output very-close-to 0 Hz signals. Without a high-pass filter, this essentially means outputting direct current. A lot of audio gear don't take kindly to DC signals various reasons; things like amplifiers or headphones.

Most PC sound cards employ so-called single-supply designs running their chips only between Ground and a single positive supply, e.g. 5V or 3.3V. So typically for a headphone output the amplifier will swing around 1.5 or 2.5V or so. To get rid of this offset, a capacitor is used. This capacitor, together with the headphones impedance, will function as a RC hipass.

Thanks for the explanation!

That's awesome.

You truly can play quake anywhere. I always liked ttyquake, which replaced the renderer with an ascii-art output. Actually quite playable if you set your font size small enough and your xterm large enough...

definitely the coolest cyberpunk thing ever

I wonder if it could be emulated with a shader...

To bring this full circle, is anyone aware of a software oscilloscope for Windows / iOS that you could 'play' the wave file into to render his Quake demo via software?

You may be able to achieve this with GNURadio.

try baudline http://www.baudline.com/screenshots/full_screen.png

Awesome idea and execution. I’m wondering whether it would work better with an edge detection algorithm instead of using the triangle edges.

Sounds neat, but a bit complicated. You have to take those edges and turn them into an efficient set of paths for the oscilloscope to trace, and you have to do it very fast.

Treat the edges as nodes in a graph, then run a graph traversal algorithm like

http://en.wikipedia.org/wiki/Eulerian_path#Hierholzer.27s_al... algorithm adding invisible edges to the next closest visible edge if you get stuck.

One could get higher bandwidth by using the three color channels of an analog VGA output to control X, Y, and intensity.

I don't know how oscilloscopes work. Is the sound in the game producing the actual image or is it generated from something else?

An oscilloscope is a cathode ray tube that has an electron beam that can be moved around by applying varying voltages to its inputs. In this case it works as an XY plotter, i.e., you specify the X co-ordinate by the value of the voltage on one input and the Y co-ordinate by the value of the voltage on the other input.

You can display lines on the oscilloscope screen by giving a specially generated two channel audio as its input; one channel works as the X co-ordinate and the other one as the Y co-ordinate.

The game (Darkplaces which is a source port of Quake) renders a scene that has the lines to be drawn (triangles, in fact) on screen. The output of the game, i.e., the lines to be drawn on screen are sent to an audio synthesizer process(PortAudio). This process uses a sound card to create the audio. The output of the sound card is connected to the inputs of the oscilloscope which draws the lines on its screen.

So it's not the sound in the game that is producing the actual image. The output of the game is converted to an audio signal which when given as input to the oscilloscope creates the actual image.

Maybe it's just me, but the audio output sounds really cool.

Fantastic example of how constraints form art.

This was posted earlier and set off the voting ring detector. I haven't looked closely, but that may have been a false positive. Since it's a good post and didn't get the attention it deserves, we won't treat this one as a duplicate.

It was/is on top of proggit, so people must've just reposted it here en masse, driving the upvote count up quickly.

I think that explains it. Thanks!

There are currently 6 posts in the last 24 hours on this, of which 3 (including this one) point to variations of the same URL.

We don't go by that so much as whether the post has had significant attention yet.

I think your voting ring detection logic is perhaps overly simplistic, then. :/

(I tried to post it myself after seeing it on facebook in a swedish/scandinavian group.)

Your logic needs to be tweaked, I'm not a part of any voting ring or whatever.

I think this post has just proven that any voting ring detector without NSA-level background detail on each voting individual is broken by design.

It's a category error to expect perfection from a statistical system.

Someone should print that on the front of every textbook on economics.

Good to see that there are people in the loop constantly correcting false positives. As I said before, I like how HN changed recently. Thank you!

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