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About MJNorris

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  1. Trouble with NaNs

    Thanks a lot for sharing Jiri! Very useful
  2. Trouble with NaNs

    Hi There, I'm currently working on some general purpose scene debugging stuff and one of the things I wanted to test for is nans in my geometry, fairly straight forward using isnan(), however I am struggling to come up with a sure fire method for generating nans inside my test scene! Does anybody know of a guaranteed way of creating a nan in your geometry? Thanks in Advance. M
  3. Vellum Constraint Attributes, what do they all do?

    Thanks a lot Johner, That was really helpful!
  4. Hi Everybody, I've got a few (hopefully) quick question about Vellum Constraint Attributes! So I'm basically using the vellum grain solver, with a custom constraint network made in SOPs. I've been able to get what I think is correct behaviour by adding my own attributes for "type", "restlength", "stiffness", "compressstiffness" e.t.c However I noticed that there are some attributes that the Vellum Solver seems to add, such as "pts[]", "stress", "L" & "typehash". Not a problem so far, except when I add a SOP solver to my DOPs to dynamically add constraints these attributes are missing. I've been able to get my constraints to work by correctly setting the "pts[]" attribute, however do I also need to be working out the "stress" and "L" values? Are "stress" and "L" influencing the solver, or are they more like data out attributes? Finally, do I need to worry about the "typehash" attribute? I can't easily upload a scene while I'm at work but if you guys think it will help explain my situation better I can do it when I get home! Thanks in advance! M
  5. Custom VEX function input type

    Fantastic, this is exactly what I was after! Many Thanks
  6. Custom VEX function input type

    Hi there, I'm trying to wrap my head around custom vex functions, mainly from a theoretical point at this stage so not really addressing a specific use, just general knowledge. When I create a VEX function I believe that I have to specify exactly what type of data it is expecting from the arguments and exactly what type of data it will return. eg. function int my_function(float a){ return int(a); } in which case I have to feed it an INT argument and it will always return an INT value. My question is this, is there any way of creating a VEX function which can accept multiple arguments, but not fail if one or more of those arguments are absent when the function is called? Or better yet a way of taking a single argument with out specifying what type of data that argument should be? I'm guessing that this is somehow possible as most of the existing Houdini VEX functions work with multiple flavours of input. Thanks in advance. M
  7. Array Function VEX

    Okay, I actually got it working but those who have a similar issue I needed to use the 'funtion' function as the VEX compiler seems to be getting confused so .................... //doing an explicit function declaration seems to stop VEX getting muddled up function vector[] rgb_array() { return { {1, 0, 0}, {0, 1, 0}, {0, 0, 1} }; }
  8. Array Function VEX

    Hi there, I'm playing around with creating some custom VEX functions and came across something a bit odd that I just can't seem to get working. If I want to create a custom function that returns an array, say a vector array I will need to declare the return type at the beginning, according to the docs the following should work // A function which returns an array of vectors vector[] rgb_array() { ... }; However if I run this in a wrangle I get a syntax error on line1. Is this a bug? Or am I declaring my function type incorrectly? Thanks in advance m
  9. Hi all, I'm trying to create some physically accurate bullet sims using real world values for mass/density and friction, so I've been looking at some engineering tables for friction coefficients: http://roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm What I'm confused about is this: It seems that real world friction is calculated based on the coefficient of friction between two objects, eg wood & wood has a friction coeff of 0.25 - 0.5; wood and concrete 0.62; wood and metal 0.2 - 0.6. So friction is not a material specific attribute, so if I have 3 houdini objects, one wood, one concrete and one metal, how do I create realistic friction settings for each combination when I can only set a single friction value per object? Is it even possible? Also, how does Houdini calculate friction coefficient between two objects? Does it multiply the friction values? Or average them? Any help is much appreciated Thanks in advance!
  10. EXR meta data issues

    Thanks for the help, makes a lot more sense, although I'm finding it a bit temperamental, sometimes working, sometimes not. I'll keep investigating. Thanks again
  11. EXR meta data issues

    Hi there, I'm trying to set custom data as meta data using the mantra render attribute: "vm_image_exr_attributes" according to the docs i should be able to parse the attribute a python dictionary object, however whenever I try to do this: test_dict = {"count" : 0, "path" : "/jobs/"} my_node.parm("vm_image_exr_attributes").set(test_dict) I get the following error: TypeError: in method 'Parm_set', argument 2 of type 'std::map<std::string,std::string,std::less<std::string >,std::allocator<std::pair<std::string const,std::string > > > const &' What I am trying to achieve is a dictionary comprised of file paths that I can then check in nuke. Can anyone shed any light on this? thanks
  12. Trouble with debris shelf tool

    Hi All, I'm relatively new to Houdini and I'm working on a destruction sim of a car hitting a crystal/ice statue. I'm really close to getting a result that I'm happy with but I've hit a brick wall trying to get a fine spray of particles as a secondary effect. Here's what I have done so far: 1. import statue GEO and use a combination of cookie SOPs and Voronoi Fracture to pre-divide the mesh into groups. 2. create an RBD sim using the RBDglueObject node, bring in the low-res car proxy and use it as a collision object. 3. smash car into statue. 4. cache out the RBD as a .bgeo sequence. 5. read in the cache and everything works fine! 6. press the debris shelf tool, this is where things start getting confusing. so I'm getting several odd results, firstly I have to run the sim from frame1, despite having set the debris_sim node start frame value to the correct frame (512). I'm also really confused about the relationship between the constantBirthrate attribute of the POP_replicate node and the constantBirthRate attribute of the POP_source node. My end goal is to use the particles to instance some very simple geo with a copy SOP, however when I do this I find that where I thought there was just one particle, there are actually a load of particles, all occupying the same space, resulting in loads of copies of geo overlapping each other! I haven't uploaded a scene file because my scene is a little heavy but if anybody needs one I'll upload a simplified version with the cache as a .zip Many thanks in advance and any advice or help at all is much appreciated. M.