Author Archives: jwothke

after all those years..

To complete the set of chipmusic emulators, here my WebAudio version of SC68 – an AtariST  music emulator (that plays files like *.sc68 or *.sndh).

SC68Eventough I had done some programming on the MegaST 4 back in the 90ies, I have to admit that at the time I had not realized that the machine had anything resembling a sound chip. Those were the days of 68k assembler, DSP machine code and GFA-Basic.. and we were just doing a Paintbox software for the “CHILI” framegrabber and realtime video-effects extension card… 🙂

But it seems the ST not only did have a MIDI interface but also a built-in sound chip…

Thanks to Photon Storm for sponsoring this little project.


68000, Paula & Co.

screenYet another bit of home computer music nostalgia. This time it is the Commodore Amiga that is emulated using UADE. The original Unix Amiga Delitracker Emulator is based on a two process design where the core Amiga emulator engine and the music player’s frontend are separate processes that communicate via IPC. Using a regular Amiga emulator then may be tricky because depending on the song it expects to synchonously load additional data files. Obviously this is on a collision course with the concepts available for an HTML5/JavaScript page.

Bringing this one to the web therefore required some redesign of the original UADE code base. Once that had been done Emscripten again did a splendid job translating the C code into JavaScript and linking it to the manually written JavaScript callbacks (see live demo here).

This experiment once again confirmed my ealier observations that the debugger support built into today’s web browsers is utterly useless (but for the most trivial scenarios). So this not only was a travel back in time with regard to home computer music but also with regard to the modern developement tools that I had gotten used to: bye bye IDE – welcome back debug/trace output.

some real JavaScript IDE – anyone?

Debugging JavaScript can really be so much fun.. first there are Firefox’s “developer tools”. These are so slow that they bring back memories of the early Eclipse Java IDE: By the time the bloody tool shows the breakpoint you have long forgotten what you wanted to look for in the first place. From there it is then a steep downhill trip: When stepping through a function in the debugger the focus will suddenly disappear and the only way to reanimate the tool is to actually remove the previous breakpoint.. LOL it’s version 31 and Firefox still has no usable developer tools.
For all those thinking ‘ahhh but Chrome is so much better’ – think again: While it is true that Chrome’s developer tools are real quick there is a catch. Or as a colleague once said: “if the result does not have to be correct my code can be real quick!”. Here is an example of a situation that you may encounter while debugging in Chrome (this is actual – non tampered with – debugger output):


The debugger here has just stepped over a line of code that sets some variable to 0. On the very next line the debugger tells you that this very variable is NOT 0.. Another fun Chrome surprise is when you find that Chrome’s garbage collector will actually trash ‘event handler’ functions that are still in use – unless you separately anchor them to some dedicated variable. 

I am so glad that I never make any mistakes as a matter of principle 🙂 So my latest bit of music playback programming could not be stopped by foul developer tools:

And what was this experiment about? xmp is a module player that plays over 90 mainstream and obscure module formats from Amiga, Atari, Acorn, Apple IIgs and PC, including Protracker (MOD), Scream Tracker 3 (S3M), Fast Tracker II (XM) and Impulse Tracker (IT) files. This functionality is now available on my little web page (click on the image above) 🙂


(You’ll find the source code here:

Fractal Flames

I just completed my latest experiment 🙂 It is a revamped Web version of Orion Sky Lawlor’s “GPU-Accelerated Rendering of Unbounded Nonlinear Iterated Function System Fixed Points” (see here).
For good measure I have added a bit of music interaction 🙂 I suggest you have a look at the live demo here (Chrome recommended). A Youtube recording can be found here.

The music I selected above is by Dexter Britain and licensed under a Creative Commons license. (see

Programming background information:

  • Starting from Dr. Lawlors opengl/C++/Windows program the main step was to get rid of any opengl legacy fixed pipeline rendering and replace it with a programmable pipeline WEBGL equivalent. Then some WEBGL limitations still had to be dealt with, e.g. adding missing WEBGL shader functions, replacement of unsupported for-loops in shaders or unsupported texture modes, etc. Luckily this process proved easier than expected. The resulting WEBGL/JavaScipt program works quite fluidly in Chome (on my GXT460). Firefox’s WEBGL implementation also works for the most part – but it occasionally it crashes for no good reason and it is rather slow in compiling the shaders.
  • Some surprise obstacles came with the attempt to implement the music playback and hook it up WebAudio’s AnalizerNode infrastructure: The first attempt to use some XMLHttpRequest based loading with AudioContext.decodeAudioData() processing proved a total failure, because Firefox’s implementation (versions 31 -33) just fails to decode the (supposedly “invalid”) mp3 data. Also it became obvious that the upfront decoding of the complete mp3 file (in Chrome) adds an unacceptable delay to the music startup. Interestingly playback of the same mp3 file works flawlessly in Chrome as well as in Firefox when using the HTMLAudioElement. So that’s what I am using now. Unfortunately that API is not implemented consistently in the different browsers and particularily the event handling in Firefox leaves a lot to be desired. But even Chrome fails to properly “loop” a song but instead goes into some corrupt state at the end of some (especially longer) songs. Once again browser specific tinkering is called for…
  • The page uses multiple AnaylzerNodes with low-/band- and high-pass filters to detect certain music patterns that are then reflected in the graphics. Unfortunately Firefox again proved a difficult customer: Connecting FilterNodes to the HTMLAudioElement here sporadically leads to corrupted music playback. Also the Firefox FilterNodes produce completely different results than the Chrome ones.

WEBGL and fractals

Did I mention that I love fractals? In fact I do and that’s why I created the below intro:


I am using orbit trap logic that I implemented in a WEBGL fragment shader.   The add-on text scrollers/messages sport an exploding-pixels effect which is done using plain Canvas pixel operations. For good measure I added my WebAudio based SID chiptune playback (see my previous posts).

I guess that next time I’d better leave all the graphics to the GPU .. because my CPU is just getting too old. In case you are using a recent browser and if you have some sort of GPU in your computer, you might try to see the online version by clicking on the above image.


“hello world 3D” version 2..

On my second trip to the world of THREE.js and WEBGL I tried out yet another bunch of “new” things:

  • use of THREE.js EffectComposers and Shaders to create “glow” effects, etc
  • creating lightweight 3D text rendering by rendering a 2D font into a texture and by creating a geometry that then represents each character as two simple textured triangles
  • create THREE.ShaderMaterials (i.e. WEBGL vertex and fragement shaders) to then apply visual effects to the above 3D text (e.g. rolling the characters or exploding the text-page, etc)


Then I came across Felix Woitzel’s fascinating “Travelling Wavefronts” demo and I had to understand how its WEBGL shader logic is done 🙂 After some tinkering I ended up with a slightly cleaned up version of my own with some added visual effect features:


After throwing all of the above together and and adding a bit of WebAudio based SID chiptune playback (see my previous experiment), I ended up with a little Web intro 🙂 Those with a reasonably fast GPU may see it in action here  (due to my old CPU I really like to use as much of the GPU’s power as I can..).


WebAudio ahoy..


At last Firefox and Chrome seem to be making steps forward with regard to audio 🙂 .. giving me an opportunity to migrate my Flash based music player (see previous experiment) to an HTML5-only implementation.


Using Emscripten I compiled my C code into JavaScript and hooked it up to the new experimental WebAudio APIs (ScriptProcessor, etc)… what can I say.. it works (see here).

PS: Unfortunately Chrome and Firefox still don’t seem to be on the same page with regard to correct chaining of Nodes.. still some work to be done.

“hello world” 3D with a pinch of concurrency..

By chance I had recently come across a very cool 3D web page and thereby discovered what modern web browsers meanwhile are capable of.

The experiment here is my THREE.js based equivalent of  “hello world” – which I did to just get a first glimps at what it means to do 3D in the browser (the live version is here).
I added a Web Worker based fractal generator to experiment a bit with the benefits of a respective asynchronous approach.

Eventhough they haven’t managed to get the tranparency handling right yet (see here), the guys at THREE.js are certainly doing a great job abstracting from the ugly details of WEBGL wiring! (What they don’t seem to have any clue about is API management and backward compatibility..  e.g. repeatedly inverting the orientation of their 3D coordinate system from one version to the next.. LOL)

more of the same in blue..

Having the building blocks of my SID player available (see earlier posts), it really was no brainer to take up the suggestion of a colleague to take his Rockbox version of a MOD player and also turn it into a Flash version (it took about half an hour).

To try out at least something new, I decided to tap the WebService of a popular chiptune page and learn how that is done with PHP. Also I am using AJAX to integrate the resulting data.

As I had already done in my SID version I am using a PHP/cURL based proxy script to work around the Flash security restrictions and load the music files indirectly from the respective domain.

The result can be seen here.

Joomla, jQuery, et al.

This next little experiment led me into the world of Joomla 2.59 (an open source CMS system). Since PHP and MySQL are among the few things that my web hoster is comfortable with, there wasn’t much of a choice really. Still I jumped at the opportunity to get some hands-on PHP5 experience.

TinyRSidMainAs expected a simple Joomla site was quickly setup with pre-existing building blocks like user management, commenting functionality and a simple release system to share my source code. Also it came as no surprise that the ‘point & click’ based Joomla software development approach got hairy once I needed my own custom functionalities. With hairy I mean the energy that is wasted to find the different places (e.g. via plugins, modules and component config or site templates) that need patching to rectify the “incorrect turns” that the “framework” is otherwise taking (or to just add missing hooks).
ImageTo make the music player from my previous experiment a bit easier to use I decided to put it into its own floating window and integrate it with some HTML based playlist functionality. After some failed attempts to get my floating window re-positioning code to consistently work in different web browsers (using “plain HTML”), I ended up using jQuery which solved the respective problems just fine. jQuery then also proved useful for the CSS based highlight/expand/collapse functionalities that I added and later it was the base for implementing a dynatree.js based file browser with “load on demand” and “drag & drop” functionality.
The final result (here) turned out quite as I wanted.

Still I was somewhat surprised about the “immaturities” that sometimes manifested in the above tools. With that I mean that eventhough I used these tools superficially at best I already ran into a couple of bugs which previously had gone undetected – which does not speak for thourough testing. However it was a pleasure to then witness the speediness with which these bugs got fixed once they were reported (I hope they also created a new testcase.. ). Community driven software development at its best 🙂