Underwhelming Screenshot 5: Gelatinous Cube Eats Bunny

Significantly more whelm than previous entries, still lacking that whole voxel thing I set out to accomplish. As far as I can tell, the only thing that's not working is for some reason the voxel rendering shader can't get brick id's, which is curious as the brick creation shader is most certainly writing to the brick texture (I checked). The really amazing part about this, is how fast it runs. This is *very* real-time. This Octtree is 7 levels deep, and it took 7 frames to generate. Frame rate appeared to stay well above 40fps. It's quite mesmerising watching a bunny form out of blocky nothingness. Even though it doesn't completely work, I'm still quite chuffed, as building the Octtree and associated 3D texture took tens of seconds in the old version, where as this does it's job tens of times per second. Source for the adventurous.

GUI progress

So there's the progress on the GUI so far. As I plan on making it the usual, here is the branch on GitHub. There's nothing particularly fancy to report, it's yet another GUI framework for OpenGL, but this has the almost unique distinction of being written in C99. It's all WIP, so if you use it, don't be surprised when the next version breaks everything.

One Shiny Dragon + Source

This is viewing a hollow shell of the XYZ RGB Asian Dragon at 1024^3, using what I've written so far of my attempt to implement Cyril Crassin's GigaVoxel method. At the moment it would be optimistic to say I have partly implemented a quarter of it, but it's capable of drawing shiny dragons, and I'd like to share them :-) The original dragon has a tad more detail than 2048^3 can store, which I intend to address in the next phase of the method, mip-mapping. In the mean time, I for one always get sad when I read a blog post about something really cool, and I can't play with it myself.

GitHub - Win32 Binaries - zlib licensed.
This should build with minimal fiddling on your favourite linux distro. I use Debian, but it only depends on X and zlib, so should be easy to build. It also loves clang. It's written in pure C99, at least that's what I tell the compiler.

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Going Deeper...

To all yee who explore the source code, fair warning, it's a hatchet job. With that in mind I hope it should make a kind of sense. The first thing you'll want to look at is the Makefile. convert and convertoct convert simple Wavefront OBJ files, as output by Blender, into a format suitable for throwing at a video card. Worth grabbing the win32 binaries for the included data file, it's not in the git repo.

convert and polyview

convert turns the OBJ file into the format that polyview expects for a VBO. polyview loads the file into memory, tells OpenGL where it is in memory and how it's formatted, and runs a simple display loop. It's not terribly clever, but it does push all of the load onto the video card, leaving the CPU idle in my tests.

convertoct and octview

convertoct produces a Sparse Voxel Octtree by discarding the polygons of a mesh file produced by convert, and throwing the points (and their normals) into a buffer. Hatchet Job. So this will only work with models that have a uniform vertex density, mostly 3D scanned objects (like the dragon, and the bunny).

The Data

A 1024^3 cube is big. That's out of the box we're talking about a Gigabyte of data if we're only using a single byte per voxel, but I'm using 4 floats. This means we don't have enough video memory. Well, it's sparse, which brings it down to 900Mb. The texture data is zipped up with zlib, which brings the data file down to a much more reasonable 17Mb. It's still extracting to 900Mb of RAM though. Due to ?!?!?, the current Nvidia drivers don't like me allocating 900Mb of texture memory on Windows 7, so the drivers convert it to 16bit floats, bringing it down to 450Mb, which it's quite happy with. This doesn't seem to affect performance in this instance, as I'm already abusing the video card in plenty of other ways. 64bit executables solve this problem, I've updated the binary and now it does allocate the full 900Mb.

The Build System & Porting

The idea is win32.c and x11.c are "shivs", all platform dependant things are in there, they obey their respective OS's rules, and they toggle fullscreen when pressing F11. They call main_* functions in polyview.c or octview.c depending which one is linked. polyview.c has almost no intelligence at all, it's just a test mesh displayer. octview.c is marginally better, providing simple FPS controls, and handballing off to voxel.c. Making a osx.c shiv should be pretty easy, and I'm fairly sure I already have one laying around from an older project.

voxel.c

This is where we find the initialisation, the texture block is decompressed with zlib, and loaded into a vanilla old OpenGL 3D floating point texture. The Node Pool is loaded into the format that Nvidia requires when you're planning on breaking the legs of the GLSL standard, like I am doing here. The main brains of the program is located in the fragment shader, which this file dutifully loads and compiles it ready for the GPU to use. The final text in this file is a few lines that update variables for the shader, such as the camera position, and then render a single flat polygon covering the whole screen. As all of the work is done in the fragment shader, it will be called once per pixel on the screen (unless you're using antialiasing, then this will run horribly slow, and at no visual benefit at all, this rendering method is aliasing free to begin with). OpenGL experts will marvel at how primitively I'm drawing the quad, and possibly be driven to self harm. Pressing the R key will reload the shader from disk, useful for debugging.

render.frag

To understand this code you'll really have to read Cyril Crassin's PhD, which can be found here. The quick version is that for each pixel it traces a path through the Sparse Voxel Octtree that was built by convertoct. There's nothing more complicated than that going on, so there's currently no point comparing it to Gigavoxels. Also it does it in GLSL, as opposed to a real GPU compute language, so mine is an amusing abuse of GPU power, at best. For now...

OpenCL Compilation Tool

I wrote a simple OpenCL compiler interface tool, partially to sink my teeth into OpenCL, partially because I wanted it. Also it seems I'm one of the few who's tackling OpenCL from a pure C angle, so this code may be useful to other folks going down that path.

It should be noted, that there is already a tool that does this, clcc, which supports... well... options. All of them it seems. It's written in C++, uses Boost, etc. I encourage folks to use that one instead of mine, it's much better. But if you're a fan of KISS, then you might want to check out mine. But clcc is better. On with the show...

Invoking it displays it's usage...

D:\code\opencl\ocl>ocl
OpenCL Compiler Test Tool
(c) 2012 Daniel Burke - dan.p.burke@gmail.com
USAGE:
        ocl
                display arguments and devices
        ocl filename
                compile filename with first device
        ocl N filename
                compile filename with Nth device

The Device list is...
-----------------------
AMD Accelerated Parallel Processing
   0    ATI RV770
   1    ATI RV770
   2    Intel(R) Core(TM)2 Duo CPU     E8600  @ 3.33GHz
Intel(R) OpenCL
   3    Intel(R) Core(TM)2 Duo CPU     E8600  @ 3.33GHz

If compilation works, it tells you how many bytes the binary is. If it fails, it outputs the compiler messages. That's it. It's a single C file, the linked archive includes a Makefile for Mingw, and a binary for windows. It's so simple you should have *no* problems building it on anything. Compiles with gcc and clang with -Wall with no warnings. What more could you want? Features? Use clcc.

• The Download.
• A link to it on Github.