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particles » Yekaterina Satanina
Apr 162015

I started (finally) looking for jobs. Came across qualifications for an effects artist (mind you, I am not ready to apply to those, and won’t for some time) – and found more motivation to be learning Houdini. When The Mill representatives gave their presentation at RIT several weeks back, so many of their process shots included the Houdini interface. Two days ago, Paul Hildebrandt from Disney gave a talk on their technical pipeline and tools – and hey, guess what, there it is. I was excited to hear that Disney effects artists write calculus equations all over their whiteboards. On the other hand, it was encouraging to hear that yet other artists draw their effects out on paper before they go into 3D space. There’s hope!

This week I explored particles in Houdini and played around with the different POP forces. Made this!

Figured out how to have one force (curve force) affect the particles up to a point, and then when they reach a certain age to be affected by a different force (combination of axis and attract forces). Added color and opacity, and tried to figure out how to render the whole thing. Alright, the preset “dust puff” shader looks okay.. but let’s try to tweak it! I opened up its network and saw this:


And decided to save that exploration for another day.

However, I feel a lot more confident with particles in Houdini now. With that, back to rocks. Hey, I made those work:


I took a slightly different approach. Before scattering points on the geometry, I grouped the areas of the landscape by which way their normals were facing – and copied rocks just into those parts. Now, I was battling with the elevation attribute. I would like to spread more rocks in lower elevations, and less up high, but I just could not figure out how to reverse the elev attribute (right now it puts more rocks in higher elevations). For now! I’ll figure it out eventually.


Additionally, I decided to revamp the up close texture of the foreground. Before it just had a mountain SOP on it, which did the job, sure, but I wanted to see if I could apply what I learned from sculpting the individual rocks to the big landscape. Attribute VOPs are not so scary anymore. I took a bounding box to isolate an area of the foreground (because not all of it needs to be super detailed all the time, and I can move the bounding box with the camera if I have to), and did this:


There is a slight, medium-scale Worley noise (I wish it was sharper), a vein pattern (which should also be sharper), and a small-scale turbulent noise for smaller detail.

Also, there’s snow:


Just need to figure out how to render the snow… Tried applying some shaders to particles, came up with some interesting but not great results, will keep experimenting.

One last thing about the rocks: I did get the attribute VOP working! Grouping by normals is a working solution, but not the most elegant one. Here, I multiplied the height of the landscape by the curvature attribute, getting this map:


Just.. have to… get the color attribute… to control the density of the rocks.

I lied, here’s the last thing about rocks. Well, it’s about shading the whole piece. I used the groups I got from the geometry’s normals to drive shaders (a very basic placeholder stone shader for both the ground and the snow). Sure, it worked, but…


… but grouping by normals gives me very unnatural jagged polygon edges. Ideally, I’d use that black-and-white map from above to control where the snow goes… but once again, that will take me just a little bit longer to figure out. This closeup definitely shows that the “grouping by normals” method for shader assignment definitely does not work:


Looks kind of nice as an extreme wide shot, though.. with the sphere-y snow.