this looks great!

This is really nice. I'm trying to do something a bit similar myself, but rendering a different isosurface. For some reason, it's not working as it should though. Just wondering if you had to modify the code from Peter Triers' page a lot to get it to work.

a|x

Ah, OK. I assumed you were rendering the noise texture in realtime, rather than dumping it into a static volume texture, then rendering that. I'm trying a slightly different tack- attempting a volume-rendering of an equation using the coordinates of the ray as it advances through the volume as input.

The results I've been getting are definitely intriguing, but also definitely not quite right.
Here's a couple of examples:
machinesdontcare.files.wordpress.com/2009/06/tb_trier_borg_notright_01.png
machinesdontcare.files.wordpress.com/2009/06/tb_trier_borg_notright_02.png
machinesdontcare.files.wordpress.com/2009/06/tb_trier_borg_notright_03.png

As you can see, the view through each face of the front-face cube looks OK, but doesn't match with the view through the other faces.

Just out of interest, are you using a cube as the geometry to render the volume, or a plane? It seems unclear in Peter's writeup.

Sorry for all the questions...

a|x

Hey, I am using a cube, the trick was to draw it twice, once with backface culling and once with front face culling. I rendered one of those to a texture and the other one in the shader pass! If you would want to update the 3D texture and still want it to run realtime you should check out openGLs functionality to render to a 3D texture from a shader. Then you could make two shader passes, one to generate the 3D volume and one to render it!

Your welcome!

Hi again moka.

I got my shader working in the end. It's sort-of realtime (well on my ageing MacBook Pro, I get around 12fps at 640x360).

Here's a couple of examples of it in action:
vimeo.com/5181309
vimeo.com/5181078

You're right though, I imagine separating the texture-creation and rendering steps would probably speed things up. Unfortunately, I'd need to create a custom OpenGL plugin for Quartz Composer to be able to deal with 3D textures. It's something I'm planning, but I'm not there yet.

I'll have to look into using a cube to render the volume again. It wasn't working for me last time I tried, so ended-up rendering to a quad, and taking the frontface and backface-culled textures as inputs to the shader.

There's potential for more fun with this one, I think :D

a|x

Did you every try this in OpenCL? I updated to Snow Leopard recently, and have been tinkering with the OpenCL patch in Quartz Composer 4. Maybe this could be done there...

a\x

I must admit, lack of OpenCL support was one of the reasons I decided to upgrade my 1st-gen MacBook Pro this Summer. I'm glad I did, despite niggles like the lack of an Expresscard slot (no biggie, really, as I never used the one on the old machine), and, more annoyingly, the lack of composite/S-Video out (I used to use the old machine as a video-player, connected to my TV).

My experience so far of using OpenCL in Quartz Composer has been mixed, I must admit. I'm intrigued by the possibilities, but it's flakey in Snow Leopard at the moment. I've been getting lots of crashes, quite a few of which have been of the nasty kind, requiring a hard-shutdown.

I'm going to try and emulate some of the things I used to do with GLSL shaders, so I can make some kind of meaningful A/B comparison in terms of speed.

What's the deal in terms of OGL 3 on the Mac? I was hoping for some kind of Geometry Shader patch in QC 4, but no such luck, sadly....


a|x

I've not really looked at GLSL #130 yet. I wonder if it's much different from the current version.

a|x

You might be interested in the camera input-as-volume raycast setup I've been tinkering with. I managed to work around Quartz Composer's lack of 3D texture support.

a|x