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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.
Along with the important concepts we've discussed so far in this chapter, the production of dynamic simulations that fulfill the needs of our projects will also require that we understand some basic concepts regarding the way our physics simulator is working. One particularly essential piece of information is that, like moving pictures, animated sequences, and the like, the production of a dynamic simulation--or, more specifically, the collision calculations in the simulation--will be dependent on a frames-per-second setting.
This and related settings will greatly influence the final outcome of the quality of any dynamic simulation we produce. To explain: if for instance, we are working in our 3Ds Max scene with an animation frame rate of 30 frames per second set, then our simulation engine will take 30 collision calculations, or simulation steps, per second. If, however, we were to work at 24 frames per second, well, our collision calculation rate would also drop down to 24 per second.
This means our simulation would naturally be faster due to the reduced number of calculations per second required, but also less accurate than the previous 30- frames-per-second example. Now, if with this were the only method of controlling collision accuracy in our simulation engine available, well, we could find ourselves in a little bit of trouble. Thankfully, in any good simulation engine, we have other options available to us, such as enabling subframe calculations. This will allow the physics engine to essentially subdivide each frame of animation playback time into a smaller chunk.
So, if at an animation playback rate of 24 frames per second, we were to introduce a single subframe or substep calculation into the simulation-- assuming of course that this option is available in our physics engine, which it is in MassFX-- well, in this situation, our engine would now be able to take 48 collision calculations per second instead of the original 24, which would naturally result in a much more accurate simulation. This increase in both the number of calculations per second and simulation accuracy will continue as we add more subframe sampling, or substeps to the process.
At 2 substeps, we would be taking 72 calculations per second. At 3, we would be getting 96, and so it goes on. Of course, we do need to keep in mind that these extra calculations and the resulting increase in accuracy will come at the cost of extra time required to complete the calculation process. Understanding how this division of time and calculation steps works really is extremely important when it comes to effectively managing the quality and completion times of our simulations.
In our next video, we'll move on to a consideration of the different object types we can work with in our dynamics simulations, specifically the difference between rigid and soft body object types.
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