Wednesday, April 13, 2011

Modeling in Houdini

The best part about modeling in Houdini is having all the tools at your finger tips.  Hit of a tab key, type what you want and you got it.  If you're a destructive modeler (usually character modeling) you'll probably just live in the viewport and sculpt away.  However, if you're a procedural modeler (usually environment/prop) you'll find yourself working more closely with the nodes.

I found that, when modeling in Houdini, you really have to think about the big picture before you start, especially when modeling procedurally.  It's not the easiest thing to do because any one node on the chain could affect the end result, so you have to plan out where and what you want affected ahead of time.

Like a lot of modelers I start off with a 2D image slap it on an image plane and start hacking out the form.  Unlike Maya, the way to do this in Houdini is press the d key, for display options, go under the Background tab and select an image.  Keep in mind that by default Apply Operation To All Split Views is checked on.  If you don't want the image on all of your views remove this option before you check off Display Background Images.  To adjust the way you look at the background image go to the 3D Viewport tab.  Unfortunately, if you are using single view and you switch views using the space + 1, 2, 3, 4 options the background image will not change because that background image is attached to the "view".

From here it's just a matter of getting to know the nodes, where to put them and what you can do with them.

Typically you would model in the SOP/ Geometry level and animate in the Object/ World space.  So that your Object level will hold all your individual characters, props, and environments.

Some really handy nodes:

Merge - you can only see one node/ node chain at a time in the geometry level so you need a merge node to combine the node/ node chains together

Object Merge - allows you to extract any node in the chain to work on elsewhere.  For example, you can use this for visualizing your end result as your working on the nodes above.

Null - is a place holder which you can add custom parameters used to drive other things.  Usually used as an "out" placeholder at the end of a node chain, so if other nodes are dependent on the end of the chain, you don't have to keep changing the last node.

Fuse - will merge points, edges, faces together

Crease/Facet - it's a little tricky understanding hard edges in Houdini.  It seems like everything is smoothed when rendering so if you need a hard edge you need to add more edge loops or you can add a crease node.  But with the crease node you won't be able to see the result until you render.  If you use the Facet node/ Cusp Polygons you will get the hard edges but that's because it actually breaks apart the edges (which is probably not what you want).  Best bet is probably add edgeloops, but then you're creating more polys so choose your weapon well.

File - use this to write your your geometries or read them back in.

Group Geometry - allows you to select a group of points/edges/faces and put them in a group which you can name.  The group name will then be an attribute you can use later on down the chain

Delete/Blast - Blast is pretty much what gets laid down when you hit the delete key.  If you have a group geometry before this node in the chain, you will find the group name in the drop down menu for you to blast.  Delete is similar to blast but has way more options, like deleting by expression or delete with bounding box.

Visability - if you want to hide parts of the model while your working (this does not delete the geometry so don't forget it's there).  You'll notice the visibility flags in the geometry level is just for displaying that node vs. another.

Sweep, Resampling, Skin - great for making tunnels, cables, rails, etc.

Point, Attributes and Primitive - these are also really great nodes to use but I haven't mastered them yet


* q key repeats the last node, to template more then one node hold down the ctrl key when highlighting the template flag

Really awesome example of procedural modeling: cmiVFX: Road Creation

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