The slides for my talk on XPBD are now up on the publications page, or available here.
I spoke to someone who had already implemented the method and who was surprised to find they needed to use very small compliance values in the range of 10-6 to get stiffness comparable to regular PBD.
The reason for this is that, unlike stiffness in PBD, compliance in XPBD has a direct correspondence to engineering stiffness, i.
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Anyone who has worked with Position-Based Dynamics (PBD) in production will know that the constraint stiffness is heavily dependent on the number of iterations performed by the solver. Regardless of how you set the stiffness coefficients, the solver will converge to an infinitely stiff solution given enough iterations.
We have a new paper that solves this iteration count and time step dependent stiffness with a very small addition to the original algorithm.
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Just a quick note to say that the pre-print for our paper on particle physics for real-time applications is now available. Visit the project page for all the downloads, or check out the submission video below:
The paper contains most of the practical knowledge and insight about Position-Based Dynamics that I gained while developing Flex. In addition, it introduces a few new features such as implicit friction and smoke simulation.
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FLEX is the name of the new GPU physics solver I have been working on at NVIDIA. It was announced at the Montreal editor's day a few weeks ago, and today we have released some more information in the form of a video trailer and a Q&A with the PhysX fan site.
The solver builds on my Position Based Fluids work, but adds many new features such as granular materials, clothing, pressure constraints, lift + drag model, rigid bodies with plastic deformation, and more.
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Slides for my SIGGRAPH presentation of Position Based Fluids are available here:
http://mmacklin.com/pbf_slides.pdf
During the presentation I showed videos of some more recent results including two-way coupling of fluids with clothing and rigid bodies. They're embedded below:
Overall it has been a great SIGGRAPH, I met tons of new people who provided lots of inspiration for new research ideas. Thanks!
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Working on a distributed team means that often the best way to share new results is via video captures of simulations. Previously I would do this by dumping uncompressed frames from OpenGL to disk, and then compressing with FFmpeg. I prefer this over tools like Fraps because it gives more control over compression quality, and has no watermarking or time limits.
The problem with this method is simply that saving uncompressed frames generates a large amount of data that quickly fills up the write cache and slows down the whole system during capture, it also makes FFmpeg disk bound on reads during encoding.
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Position Based Fluids (PBF) is the title of our paper that has been accepted for presentation at SIGGRAPH 2013. I've set up a project page where you can download the paper and all the related content here:
http://blog.mmacklin.com/publications
I have continued working on the technique since the submission, mainly improving the rendering, and adding features like spray and foam (based on the excellent paper from the University of Freiburg: Unified Spray, Foam and Bubbles for Particle-Based Fluids).
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This post is about generating meshes for finite element simulations. I'll be covering other aspects of FEM based simulation in a later post, until then I recommend checking out Matthias Müller's very good introduction in the SIGGRAPH 2008 Real Time Physics course [1].
After spending the last few weeks reading, implementing and debugging meshing algorithms I have a new-found respect for people in this field. It is amazing how many ways meshes can "go wrong", even the experts have it tough:
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This is a quick post to document some work I did while writing a mass spring simulation using an implicit integrator. Implicit, or backward Euler integration is well described in David Baraff's Physically Based Modelling SIGGRAPH course and this post assumes some familiarity with it.
Springs are a workhorse in physical simulation, once you have unconditionally stable springs you can use them to model just about anything, from rigid bodies to drool and snot.
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Hi all, welcome to my new site. I've moved to my own hosting and have updated a few things - a new theme and a switch to MathJax for equation rendering. Apologies to RSS readers who will now see only a bunch of Latex code, but it is currently by far the easiest way to put decent looking equations in a web page.
It's been a little over a year since I started working at NVIDIA and not coincidentally, since my last blog post.
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