mr equivalent of brickmap?

[1armedScissor]

Can anyone tell me if there is a mentalray equivalent of renderman's brickmaps?

Thanks in advance everyone.

[bart]

Depends on how you are using brickmaps. And at what level are you talking about. For example, there are several mechanisms available for shader writers to make re-usable data caches of sorts. And there are some new techniques coming out in 3.7.

Aside from implementation, what kind of effect are you trying to achieve?

[1armedScissor]

Point Clouds.

[bart]

That is an implementation. What are you using the point clouds to do?

[1armedScissor]

for caching things like occlusion and indirect illumination

[haggi]

I think in 3.6 you have to do it yourself. You can render a lightmap and save the points into a pointcloud file. If you follow the pointCloud file format from pixar, you should be able to execute brickmake.

If you want to do it completly in mentalray you have to do the LOD or mipmapping youself because there is no such mechanism in mentalray. But it should be not too difficult to implement an octree which gives you different resolutions at different distances.

[1armedScissor]

Thanks Haggi, we'll give this a shot.

[bart]

In 3.7, there are particle maps, and there should be a particle map documentation that comes with that. But the tutorial doc for it might not be out yet. I'll keep you posted.

[caml]

We had some success with the light map to ptc approach. I did not put the tool together so I do not have all the details.

Basically 1 object + 1 shader + 1 point samples file (where to sample) = 1 ptc file

The main draw back was it was very similar to 2d texture baking and shared some of the same issues.

Imagine you have a car with hundreds of parts and you wish to bake occlusion to texture. You have to bake hundreds of maps and manage them. Also you end up with maps that are way too big (say a 2k map for a couple of bolts), and others that are too small (the same 2k map may not work for the hood of the car).

What we were really after is somthing that is more camera based. When mental ray writes an image it takes several samples per pixel and filters the results as an image. What we want to do is write out these samples prior to image filtering and store them at world space P and N of that sample. This is more or less what prman does with bake3d. This presents certain challenges of occlusion (to the eye, not ambient occlusion). There are a few different techniques you can use to get around this issue. There are a couple other minor issues such as radius size of each point sample but you can get around that aswell. We would be very keen to hear about any developments to write out this type of data to some sort of open format.

cl