Category Archives: Digital Assets

Houdini digital assets I’ve made.

Sprites On Points Digital Assest

Sprites are pretty cool, but in a clean install of Houdini you can only use them on particles using the Sprite POP. It turns out, you can add some attribute trickery to make sprites work on plain ol’ points. The cooler thing is that this Sprite SOP concept works in Houdini Escape (which doesn’t have particles). I wrote a full blown help for it too, with an icon and all – which basically copies the Sprite POP language and replaces “particles” with “points”. Yes, this has been done before. But let’s face it – that one’s old.

You can find it on my Houdini page or you can get the asset directly from here.

For those interested, here are the attributes you need to get sprites on points:

  1. spriterot: class: point, type: float, size: 1
  2. spritescale: class: point, type: float, size: 2
  3. spriteuv: class: point, type: float, size: 4 (spriteuv[0] = U-offset; spriteuv[1] = V-offset; spriteuv[2] = U-scale; spriteuv[3] = V-scale)
  4. spriteshop: class: point, type: string

Houdini Occlusion Asset

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).

  1. v1: Initial Release

Houdini BRDF Asset

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).

  1. v1: Initial Release
  2. 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.
  3. v3: Added string input parameter so you could select the BRDF type after promoting the inputs.