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KarlRichter

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KarlRichter last won the day on November 12

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About KarlRichter

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  1. Packing tiles for mosaics

    A while ago, I was working on a project that had lots of animated tiles. It is actually quite a tricky problem to pack a bunch of shapes together with the smallest amount of "grout". While researching this, I stumbled across this paper "Simulating Decorative Mosaics" by Alejo Hausner, and thought this would be a perfect thing to implement in Houdini! Here is the input, the houdini logo: Also needed are curves that represent the color or element boundaries: Here is one iteration of the loop. This is basically the result you would get copying tiles using a scatter and copy sop: After running the loop for fifty iterations, the tiles seem to be pretty well packed, and are respecting the boundary curves very well: And lastly, here is a version with randomized tile sizes. Still works pretty well! While I never actually ended up using this in production, But I thought it was pretty cool and could be used for other stuff, like maybe packing houses in a procedurally generated map or something. Anyway, here is an example .hip file if anyone wants to play around with it: mosaics_example.hip
  2. I have used this setup on a number of projects and thought I would share. Basically, it is a simple setup that uses the wire deformer and hair system to animate geometry. I used to do this all the time back in Maya using Shave and a haircut, and was surprised that there isn't a more straightforward method to do this kind of effect in Houdini. This is especially useful when you need to add flowers or other kinds of detailed grass to an existing grassy field that has wind blowing through it. grass_example.hip
  3. Vellum substep issue.

    Increasing the pscale without changing the constraint length is what is causing this sim to behave strangely. When the pscale is increased, it is making the sim fight against the constraint length and creates interpenetrations. At low substeps, the behaviour is not as noticable, but is still there (run the sim with the gravity off to see what I mean). This could be solved in a number of ways: - Turn off self collision. - Use another sop to run over the constraint geo and increase the length along with the pscale. - Turn down the stiffness of the stretch constraint.
  4. building 3D frames from mesh geo

    In 17.5, the measure sop has been improved. If you set the measure type to "curvature" and "Principal", you can then choose to output a direction vector.
  5. Evenly Distributed Hexagons On A Object

    Here is a cool trick that will work just for hexagons. Use a remesh node to turn your mesh into nice even triangles, then use the divide node with "compute dual" checked. Instant hexagons! Edit: Well, never mind. I guess that makes some pentagons too. Oh well...
  6. keep uvs on flip anim

    A while back i was playing with the UV fluid mesh seam issue with some amount of success. See attached for an example. uv_fluid_mesh.hip
  7. Your scene is using some external hda so it doesn't open right for me, but I suspect that you are over the geo display limitation. It is very easy to go over this threshold with instances because it's so easy to make so many of them! The default is set to 20 million polygons in the display options -> optimize tab.
  8. Liquid mix export to Maya-Arnold

    To be able to access alembic point data exported from Houdini in Maya with Arnold, you must export the attributes as vertex color data. The trick here is that it MUST be a color type attribute in houdini, a regular vector will not work, and it MUST be a vertex class attribute. So if you were to create a color node and use one of the RGB channels as your "weight", and then promote it to a vertex attribute it would export properly. In order to access this data in Maya with Arnold, you need to check the "Export Vertex Colors" box under the Arnold tab on the alembic shape node. Then you can use the "aiUserDataColor" node in a shader network to put your weight attribute to work using a ramp or something. Also, you can get motion blur data from alembic files with changing topology this way as well. Export your velocity vector as a vertex color and then use the "motion vector source" attribute on the shape node to access the velocity data.
  9. Grains - how to make 'em bounce off surfaces

    Look closer. I know it seems like setting ispbd to 0 would disable the grains entirely, but it doesn't! The particles bounce, but still maintain distance. It's hard to see in your test scene so I made one that illustrates this better. ispbd_test.hipnc The ispdb flag does not disable grains, it is there to tell the pop solver that a given particle is under control of pdb, so don't apply all the regular pop physics. Indecently, before I was aware of this flag I would fake a bounce by giving each particle a random upward velocity on the first impact.
  10. Grains - how to make 'em bounce off surfaces

    Set the attribute "ispbd" to 0. See attached. collision_grains_v02.hipnc
  11. Bee Movement

    Here is a quick example of how you could achieve this kind of effect with the grain solver. If you wanted to get fancy with this, you could constrain pairs of grains together to more accurately represent the bee body shape. bees.hip
  12. 2D vellum Simulation

    If you use a sop solver to explicitly set the y point values of the cloth geo and an additional sop solver to do the same to the constraint geo, you can very effectively constrain your sim to just two axis. See attached for example. BTW, it may seem that you only need to manipulate the "Geometry" data, and in the simple attached demo that seems to work fine, however I have found that with complex vellum sims you really need to run over the "ConstraintGeometry" data as well. vallum_x_constraint.hip
  13. HTOA missing shaders in new versions

    The Arnold shaders are under "shading", but the "skin_SSS" shader has been deprecated as of Arnold 5:
  14. Here is an example using rest fields to drive displacement for the purpose of adding detail to a smoke sim, but it could be used for any kind of displacement. There is an example .hip in the Vimeo description.
  15. cloth capture weights

    Is there really no (easy) way to edit the weights generated by the "cloth capture" sop, or am I totally missing something? It seems like the "edit capture weights" shelf tool should do it, but I guess it's for bone weights only. Kind of a big omission, especially with the the addition of the new Vellum stuff. What is the solution to transfer a low res cloth sim to a hi res asset? I am currently getting ok results with the point deformer, better then with the cloth deformer, but it would be really nice to adjust weights on a more granular level. I have been comparing the results between the new vellum cloth and Mayas ncloth for use in an upcoming project. While I have been getting pretty good (and fast!) sims with vellum, I have been having issues finding a reliable way to transfer the sim to the render asset.
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