Blog Archives

unaligned “packed structs”…

are certainly not a good idea if a program is supposed to be portable. Unfortunately that is exactly what ZXTune is using to parse the different binary music files.

“One of the rules of packed structs is that you have to access them directly through the packed struct type. In other words, you can’t, in general, take the address of a packed field and then access the field through that pointer, because the pointer type won’t reflect the packed attribute.” (sunfishcode)

Unfortunately ZXTune used boost::array instances within the various packed structs.. Problem: when methods are invoked on boost::array (or std::array, etc). The ‘this’ argument to the boost::array functions may be misaligned, but the boost::array functions themselves don’t know this.

On CPUs which don’t mind unaligned memory access you may get away within without realizing that there is a problem.. and in this case it was my attempt to cross-compile the program using Emscripten that revealed the issue. Not wanting to rewrite too much of the foreign code I opted for a quickfix: replacing the boost::array with a built-in array fixed the immediate problem…

Naturally a clean implementation should better refrain from depending on unaligned memory access at all… not all the CPUs are as forgiving as Emscripten.

(click on the below image for a live demo).

screenshot

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AdLibido – the wonders of early PC music ;-)

It was back “in the old days” and I remember my relief when some day I found out that all PCs were not necessarily mute: Thanks to some “walking frame” called “AdLib” they could actually make sounds… and a bit later things became pretty neat with the rise of Sound Blaster…

AdPlug plays sound data, originally created for the AdLib (OPL2) and Sound Blaster (Dual OPL2/OPL3) audio boards, directly from its original format on top of an emulator.

My latest bit of Xmas tinkering is a HTML5/WebAudio version of AdPlug (Thanks to Simon Peter and the other authors of AdPlug.). For a live demo click on the below image..

HTML5/WebAudio version of AdPlug

WEBGL and fractals

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


turtles

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:

egaux2

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..).

egaux3

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.

jsid

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.