Ambient Occlusion Rendering

[kedojo]

btw: did anyone FIND a max/vray occlusion shader? I haven't seen much out there...

I guess at the very least, if you have max 6 you could use a mental ray occlusion shader and render out a pass that gets composited into your vray rendering.

[RErender]

Except in using it to effect recesses for a dirt shader or the like, isn't the result of the one GI bounce method indistinguishable from the output of a "true" occlusion shader?

[Seraph135]

The occlusion shader enables the material to cast rays from various points on the surface in order to collect distance values to the nearest object. The smaller those distance values, the darker the pixel is shaded and vice versa. Shading is then based on the proximity of objects, as opposed to being based the number of skylight rays that hit an object (as in a 1 bounce skylight).

I think in most cases your right RErender, but imagine an object at the far end of the inside of a warehouse with light only from one end. That object may have nothing near it except the floor. A skylight render on this scene is going to act the way light does and that entire object might be completely in shade. Where the method described above is not effected by light but by distances. Maybe not the best example, but I think it still illustrates the point.

If you chose to do several vray occlusion passes and comp them together you would probably get really close again. But it would require more than one pass and some trickery.

[kedojo]

Yeah Seraph - exactly - a skylight render will be affected by levels of "blockage" (like your warehouse) between the sky and the object in question.

That's why I don't think it's usefull to think of occlusion as a substitute, or even enhancement for GI. Especially since GI is becoming increasingly easy and fast to setup (btw, since occlusion still requires a large numbers of rays cast for sampling purposes, there's not much of a speed increase).

That's why I'd leave it for NPR or special effects use, like cartoon shading or baking a dirtmap - it requires some experimentation but can be very cool!

[Psy]

the dirtmap plugin written by daniel rind was originally done for max and there is still a beta out there, but the one for xsi is much more complete and finished.

still nice tho, but im def gonna have to give it a go again and see how well i can get a similar effect. might just be faster

[Da_elf]

dirtreyes is an occlusion shader of sorts
http://www.reyes-infografica.com/plugins/dirty.php