View Full Version : Wich AO aproach?

02 February 2005, 04:41 PM
Hi guys;

I was wondering with method do you use to do Ambient Occlusion now that there many ways to do that (at least three), Dirtmap?, ToLight shader?, or the one coming with MAYA 6.5?

Thankīs in advance.

I like Dirtmap so you can make normal textures also and you can especify the vector of the dirt but Iīd wanna know your opinion.

02 February 2005, 06:02 PM
Dirtmap is not appearing in my MR Shader creation menu. I switched to the one from Alias. It's good and fast. I miss dirtmap now.

02 February 2005, 06:17 PM
surely 6.5 supports the dirtmap shader?

02 February 2005, 06:22 PM
>surely 6.5 supports the dirtmap shader?

It might work, but I didnt try.

02 February 2005, 07:56 PM
Yes, Dirtmap works in MAYA 6.5, thatīs why I ask this.

Lazzhar you donīt miss that things that have Dirtmap but MAYAīs one donīt?

02 February 2005, 09:51 PM
joie, I think you cannot set direction of the vector to calculate the AO in dirtmap, but recently I'm not doing a lot of rendering, too much modeling and other stuff. That's why I'm not up with AO renderings:curious:

02 February 2005, 11:32 PM
Of course it can do it, although it may produce funny results in some kind of surfaces, it do it perfect on flat surfaces, itīs interesting.

Any more opinions?

02 February 2005, 12:25 AM
The other way of doing an AO pass is through Final Gather. Run a seperate pass with no textures on your objects with Final Gather and that will give you an acceptable (in most cases) AO pass. Of course you have to deal with rendering final gather and the issues that it incurs.

02 February 2005, 12:53 AM
I find AO goes great with a nice red wine. Smooth, with a slightly fruity aftertaste.

oh yeah, the dirt shader does nice AO.

02 February 2005, 09:49 AM
But have anyone of you guys migrate to another approach since it comes standard with MAYA?, do you use it?, or do you still using Dirtmap (or the one you used to use)?

03 March 2005, 09:02 PM
joie, what do you say? Is there any real difference between the results of AO in Maya 6.5 and dirtmap?

Anyone else see any difference? I have not compared them carefully yet.

03 March 2005, 09:53 PM
I've been using both the Dirtmap and the Mib_amb_occlusion shaders lately and they both seem about the same to me, though I'm not using any of the normal output modes etc. One thing though, the Mib_amb_occlusion is much slower than the Dirtmap by default, because the Dirtmap by default has a maximum ray distance already set on it (so that after a certain distance from a point it stops looking for geometry) whereas the Mib_amb_occlusion doesn't, it looks as far as it needs to even if the contributions from far objects are negligible.

So to speed up the Mib_amb_occlusion shader you can specify a value in it's Max_distance parameter.

03 March 2005, 11:03 PM
I mean, Dirtmap have more options, like the bent normals output and take color from environment and that short of things, and the one coming with maya doesnīt, but have the reflection mode wich is cute, thatīs what I mean.

03 March 2005, 11:19 PM
Actually, the one that comes with Maya has 2 different types of bent normals and has a mode to sample the environment. The only thing it doesn't seem to have is the vector control.

You control what the shader does using the Mode value. Mode 0 is just occlusion, mode 1 is occlusion and the environment colour (or if you set the 'dark' colour to white you can get just the ambient colour with no occlusion), mode 2 is bent normals in world space and mode 3 is bent normals in camera space.

The bent normals in world space (mode 2) is the same as Dirtmaps, only it's been re-ranged. Dirtmaps bent normals are in the range of -1 to 1, so without using a Set Range node to remap them to the 0 to 1 range of an image (or you could render to HDR) you're only getting the positive direction along each axis I think. The amb_occlusion shader already has the normals remapped to the 0 to 1 range.

The thing I'm wondering about though, is why is the result slightly different when I go:

samplerInfo.normalCamera > Set Range > Surface Shader.

Is that in object space or something?? Because that's what I use for generating normal maps.

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03 March 2005, 11:19 PM
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