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catchyid last won the day on October 11

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About catchyid

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    Khaled Abdelhay
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    Montreal, QC

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  1. rbd clustering + constraints

    Another related Question: I have a bridge made of cement and brick wall --> the brick wall has maaaaany disconnected bricks so the logical thing to do here is to create a proxy mesh (e.g. vdb from poly, back to one big mesh) and use it for sim, HOWEVER, I am thinking: what is the best way to animated bricks based one proxy mesh? one idea is point deform? another idea is using primitive intrinsic transform but I am afraid that would be tricky as any slight error in math would produce wrong result (e.g. not using pivots, using full transform vs transform etc.)? I am looking for the simplest, bullet proof method
  2. rbd clustering + constraints

    I have not got time to look at details, but just looking at the constraints network (fully connected!) makes me feel like WOW Thanks, I need to look in details to learn more, but for now thaaaaaaaaaaaaanks for your help
  3. rbd clustering + constraints

    Hi, I want to do something simple, yet not sure how? I have 4 columns, 1 window --> my goal: 1-break columns, cluster column pieces (combine pieces), create constraints in columns given the new clusters --> done 2- break window --> done 3-cluster window pieces --> problem: "cluster" node works universally, cannot say cluster only window? Any solution? 4-create constraint between window pieces --> done 5-create constraint between walls and windows --> problem: i don't find a way to attach windows to walls? this is the most important thing here? without constraining windows to walls, windows will fall once simulation start as they are not glued to any thing? Question 5 is the most important one if someone has some ideas (am sure it should easy), plz let me know PS. hip file attached.... Cheers constraints_question.hip
  4. bullet constraint_type

    just an update if someone has the same question: "glue" has no constraint_type, only 'hard' and 'soft' can be 'position' or 'rotation' constraint_type
  5. bullet constraint_type

    Hi, In dop one can add "Glue Constraint Relationship" to determine the type of the constraint (so "Glue Constraint Relationship" is Glue, "Bullet Soft Constraint Relationship" is Soft). Now, if these DOP nodes determine the type of the constraint, then what's the value of having SOP "constraint_type" primitive attribute? I "remember" it has values like "all", "position", "rotation", but I am not sure if it would make sense to say "Glue" but only "position" (it will be similar to "hing" but is this the right way to use it?) Thanks
  6. vortex filament example?

    Thanks everyone, I guess a lot of things to read about now
  7. vortex filament example?

    thanks guys, since they are fluid simulator, can they be replaced pyro solver? i.e. what makes them special to have their own solver? I think they are scaled down version of the a fluid simulator that sims only circluar vortexes (so they can sim only this kind of motion but fast)? it's like a ripple solver vs flip solver? thanks again
  8. vortex filament example?

    hi, I am tying to understand vortex filament simulation, found one example in houdini docs but still cannot get it? vortex filament : is it a line where its tangent is the center of rotation? can it be a line or must a closed curve? Thanks
  9. Hello, -smokeobject has 'source' mask scalar field --> I assume it should be set to 1 where density is being emitted, however it's always set to 1 and covers the whole sim box, is that normal? Plz see attached file -My goal is to define "age" scalar field and change the sim such that 'older' voxels gets more buoyancy (Okay, I admit, the idea is not clear yet, but my goal is to advect density for let's say 10 frames and after 10 frame change dissipation , apply force, etc...so, I need to have 'age' in terms of frame count, so when a smoke is just emitted the voxel will have age 10, then each frame it goes down by one until it reaches zero) Thanks smoke_mask_question.hip
  10. Pyro: Loosing Velocity in sim?

    Hi I have a pyro sim where I add a preroll velocity noise, my goal is to make density move quickly once it's injected in the simulation (i.e. I don't want to wait couple frames before I see density moving, note: density has a velocity field as well, but it takes also couple frames to move the smoke). Anyways, something I've noticed, when I add the pre-roll velocity noise field, it modifies the sim velocity field then quickly die or damped? is this normal? Thanks,
  11. Example for Deformation Wrangle SOP VEX?

    Thanks, I see a sample code. What made me initially curious is: If this node runs vex code on points to deform them, then why cannot just use a normal point wrangler? Also, I need to check the derivatives option because I am not sure how to use it. Okay, I admit, I need to read and test more
  12. Hello, I am doing a mesh deformation and found this SOP node "Deformation Wrangle" which runs VEX code, does anyone has an example on how to use it? I use lots of vex wranglers, but never seen this one before? Thanks,
  13. Hello, I am trying to understand what is the difference between pretranslate and translate (in order to understand the code below which applies points transforms to RBD primitives). Note, in the code below, orient, pivot and P attributes come from the points attributes matrix xform = qconvert(orient); //convert quaternion into 4x4 rotation matrix, checked and 4th column is [0 0 0 1], i.e. no translation pretranslate(xform, -pivot); //what does it mean? maybe xform= -pivot * xform *pivot translate(xform, P); //does it mean xform = xform * P, i.e. just add the translation component to the existing one in the matrix? v@P *= xform; //-- I have a question: I assume Bullet uses center of mass for rotation, hence we have "pivot" attribute? and "P" is just a pure translation in world coordinates? Thanks,
  14. Hi, I did a quick test where I have a guided box that is controlling a car model. Glass (which has glue constraints), works fine with guided box, basically it breaks on collision. However, the car body which has soft-constraints bounces a lot on collision and keeps on oscillation. Is this behavior normal (i.e. guided animation forces soft-constraints to bounce)? The goal is to deform car body, hence I am using soft-constraints... Thanks,
  15. just if someone is interested, I got an answer from SideFX support: matrix xform = qconvert(orient); pretranslate(xform, -pivot); translate(xform, P); If you're applying that to a piece that already has a transform, its new transform would be `piece_xform * xform`;