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This course introduces basic physics simulation principles in Autodesk 3ds Max using MassFX, a system that makes it cost effective to animate rigid body objects, cloth, and particle systems. Author Brian Bradley introduces basic concepts such as gravity, drag, volume, and density, and how Newton's Laws of Motion can help you understand the interaction of objects with these unseen forces. Using the purpose built scene, Brian walks through the tools and features of the MassFX (PhysX) system, applying the principles discussed as he goes. Along the way, discover how to combine rigid bodies and constraints, mCloth fabrics, and mParticles geometry to create fairground-style effects.
Having taken a look at substeps and Solver Iterations already, the final accuracy option that we want to take a look at for now is this Generate Shape Per Element checkbox. This option, when on, lets us create a separate physical shape for each element in a geometric object-- that is, once we apply a MassFX rigid body modifier to it. When off, as it is by default, MassFX creates a single physical shape for the entire object. This option obviously is likely to be less accurate, but it can stimulate faster, hence it being the default.
To demonstrate how to Generate Shape Per Element option works, let's again make use of our old friend the 3ds Max teapot primitive. Now, this particular object, as you may know, consists of four elements. If we just select a teapot, right-click, and Convert to Editable Poly, we can enter subobject element mode. Now, as we click through our geometry, you can see it consist of a body element, a handle, a spout, and a lid. Four elements in total. With that established, let's just come out of subobject mode and apply now a MassFX rigid body modifier.
As stated, by default we get a single physical mesh that unfortunately leaves quite a number of concave areas on the object blocked. Clearly, objects would not be able to pass through out of this handle area, nor over here or by the spout. Naturally, these blockages could lead to a potentially inaccurate simulation. If, however, we now and able the Generate Shape Per Element option and again apply a rigid body modifier, well, this time to our second teapot, you can see that whilst we do still how some blocked-off concave areas such as the inside of the handle, we can nevertheless see that the physical shape, or rather shapes, now conform much more closely to the actual or graphical mesh of to teapot, particularly over by the spout area.
This naturally will give us a higher level of accuracy in our simulations. We just need to note that this switch or checkbox applies only to subsequently created rigid bodies. We cannot switch this on and expect existing rigid bodies to switch over to a shape-per-element mode. That isn't how it works. The other option we want to look at here is found in the Display options tab of the Tools dialog, this being the MassFX Visualizer. Its function is to help us as technical artists visually debug what is going on at any given moment inside a dynamic simulation.
Essentially, we can use this set of tools to display various properties or aspects of a rigid body behavior inside a simulation as it is in process. If the simulation results we are getting are in some way unexpected, being able to see these nonrendering real-time indicators could possibly help us determine what might need to be adjusted in order to remedy said problem. To see it in action, let's just first of all reposition our teapots in the scene. We just want to give them the opportunity to collide a little.
Let's just raise them up so they have got a little more height. And of course we do want to turn on most of our Visualizer options. Clearly there is no point turning joint options on at this moment any time because we have no joints in the simulation with which to work. Now, if we run the simulation, you can see the MassFX Visualizer at work. What we are seeing here of course is a very simple set of readouts that really are not giving those much more information than we could already discern just by watching the objects as they are simulated.
However, imagine a situation where dozens, maybe even hundreds, of objects are taking part in the simulation. Being able, as we can, to step frame by frame through the simulation and get visual feedback on what each object in the simulation is doing, well, I am sure you will agree that that could be a very powerful aid to finding and fixing any problems that may be occurring. Though by no means a look at all of the global options available in MassFX, hopefully the videos we've looked at up to this point in our chapter have shown that there are controls inside the system that can and will have a significant impact on the speed and quality of our finished simulations.
Besides continuing to work with and gain a deeper understanding of the ones we have looked at here, I would strongly recommend that you become familiar with all of the global controls that can be found inside the MassFX Tools dialog, as all of them have the potential to impact significantly on the quality of our finished work.
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