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Houdini Occlusion Asset

Eugene — Sun, 04 Jan 2009 21:21:26 +0000

I’ve received a few requests for an asset of the occlusion inline VOP I used for the occlusion video so I thought I would put one together. I call it “Occlusion 2″ mainly because it’s the second occlusion VEX function. The occlusion VOP that comes with Houdini is actually the first function which gives you occluded irradiance which is a bit different from the occlusion we’re typically used to. I bet Houdini will eventually have this second function added in VOP form, but until then you can add it with this asset.

I put a help section in the asset, though as it’s not working right now, I’ll say that there is an added output called occlusion which is basically 1-coverage. Using this removes the need for the later subtraction step I note in the video. If you would like to see the help you can right click on the VOP, go to Type Properties, then go to the Help tab.

You can find the asset here (also linked to on the tutorial page).

v1: Initial Release

Houdini BRDF Asset

Eugene — Mon, 15 Dec 2008 03:04:04 +0000

I’m not sure why illuminance loops fascinate me so. It could be because I never had access to such a cool feature or maybe it leads me to re-visit classic bi-directional reflectance functions (I like the math). Whatever the reason, I decided to create a brdf VOP digital asset so you don’t need to type a lot to get the functions I describe in Part 3 of the Image Plane tutorial series. What’s interesting is that Peter Bowmar has created an asset for this already, but I wanted to learn how to make a digital asset. The interesting is that I didn’t look a Peter’s asset at all so I went about writing the code for it in my own way. It turns out we did it quite different.

One issue that arose though is that the help file and built-in Houdini icons don’t work as described in the Custom VOPs tutorial, so though the help file is written in the asset it doesn’t work right and there are no icons (at least the one I wanted to use). Another issue is that Houdini (at least in 9.5) has the limitation that you can’t get illuminance loop derived image planes from area lights.

You can find the asset here (also linked to on the tutorial page).

v1: Initial Release
v2: Adding a parameter to rough now works. The fix causes the rough not to be hidden when diffuse is used, but it doesn’t case any harm keeping it unhidden.
v3: Added string input parameter so you could select the BRDF type after promoting the inputs.

Image Planes Part 3 (Light Export)

Eugene — Tue, 18 Nov 2008 15:24:57 +0000

I’m fairly pleased with this video only because I learned a lot on my way to get this worked out. Well, I learned a lot of mistakes one could make with Houdini’s VEX like what you shouldn’t put in illuminance loops. I felt obliged to do this video since in the very first video I mentioned that I would talk about light export in the image planes. What this covers is how to get planes/passes for each light in the scene. You can find the video as well as the final hipnc file here. The final hipnc file has specular components added which I didn’t cover in the video since the technique to get the diffuse planes is so similar.

Image Planes Part 2 (An Occlusion Plane)

Eugene — Mon, 13 Oct 2008 02:39:44 +0000

Okay, so I went a bit off the track on this one. It’s loosely an image plane video and more of a “how to do an occlusion pass inside a shader then put it in a plane” video. So I’m not sure if I should keep it under the “image plane” heading or create some new one. Either way, this topic was a weird one I was wrestling so I did a lot of forum searches and made lots of mistakes (basically writing my VEX poorly). So I thought I would at least show my results so people could see what I found. What’s made this more interesting is looking into the different occlusion functions and trying to figure out why they differ and what they really give you.

Edit: In this video I use a subtract node to subtract the occlusion output from a constant float (1). Houdini user Jason M. pointed out that I could have used the compliment VOP instead which does the same thing in one node rather than the two I used. So remember that the compliment VOP is around!