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In order to best get a handle on just exactly what Reactor is--or better put, what it specifically does--it's important that you first understand the term dynamic simulation. A dynamic simulation can best be described as a process that allows the motion of one or more objects in a three-dimensional scene to be automatically determined based on the physical properties that you assign to those objects. In other words, a dynamic simulation plugs physics into the equation, using real-life properties like weight and friction and elasticity to determine just exactly how something moves or how it would react coming into contact with something else.
So it's a much different way of creating animation for a scene, allowing math and a whole bunch of behind-the-scene calculations that work off the objects properties that you assign to determine the way that things move and interact within your 3D scene. Reactor's comprehensive set of tools gives you as an animator the ability to create a wide range of complex physical simulations inside 3ds Max. Surfaces can be made to look and respond as if they're either rock hard, super soft, or anything that one could imagine in between.
The utility is capable of simulating realistic cloth, even fluid-based effects. So there's a ton of different things that Reactor can help you with in creating believable special effects for your scenes. Within that framework though, it's important to know that setting up a Reactor simulation does require that you understand a few specific things as to how the utility is programmed to work. For example, the game of Reactor is played with basically two different states or classification types for objects that are run through a simulation.
Geometry can be identified as either what is referred to as rigid body or deformable body--with the difference between the two object types being pretty self-explanatory. Rigid body objects are just that. They're rigid. Their shapes don't change over the course of an animation. So in other words, their geometry remains fixed and non-deforming irrespective of what they might come into contact with. An example of a rigid body object might be a rock or similarly hard surface like a floor or wall.
Reactor's second object type, a deformable body object, on the other hand, can change shape during a simulation-- that deformation being accomplished by the position of the object's vertices automatically changing position at various points in time. An example of a deformable body object might be an under-inflated rubber ball, or maybe something like a piece of cloth or a clump of putty. With deformable objects coming into contact with something else in the scene, might indeed change its shape in some manner.
Now something else to be aware of when working with deformable body objects: in order for the deformable body object that properly deform or distort during a simulation, it must first have a special type of modifier applied to it, the modifier being determined by the specific type of deformation that you're wanting Reactor to simulate: a soft 3D surface, a thin piece of cloth or a long flexible rope. We'll get into all that in more detail in our upcoming videos. For now, in a general sense, just realize that you'll be identifying your simulation objects in one of two ways: either as rigid- or soft body.
In building a foundation as to how Reactor goes about its business, it's also important to understand that Reactor works by organizing the objects in your scene that will be used in a simulation in something it calls a collection, with the specific type of collection you use being determined by how you want that or those objects to react to respond to the other objects in your scene. So objects in a simulation are placed into a collection, with the type of collection chosen determining just how those objects will specifically look or act.
Let's say that we want all three of the objects in our scene to respond as if being rigid. According to the way Reactor wants us to work, we'll have to add each of these objects to a collection that would read or interpret them as rigid. Does that make sense? So, let's do it. Now we are going to be going into all of this in step-by-step detail coming up shortly. So, for now, we'll just quickly set things up. After selecting all the objects, over in the left-hand screen, I've positioned what is called the Reactor toolbar. At the very top of the toolbar, I'll click on the icon that looks like three cubes.
It's called Rigid Body Collection. Now once an object has made its way into a collection, the specific physical properties that will determine how that object will respond during the simulation can then be added in. Things like the object's weight, how much resistance that object would exhibit should it be dragged across another surface, even how elastic or how bouncy the object will be will all be defined as measurable physical characteristics. Let's say that we want the two boxes to fall on the floor, collide with each other, then continue traveling in whatever direction they might.
That would require us to identify certain physical properties for each object. Let's see if we can't add a little weight, or what is referred to in Reactor as mass, to the middle yellow box. Once selecting the box, we can return to the Reactor toolbar in the left, heading a little further down. We're looking for a button called Property Editor. When you find it, go ahead and click. When the dialog opens up, up at the top under Physical Properties, we'll change the Mass to 25. That's all we need to do. Now, while running a simulation, objects can be defined as not just movable or locked into a fixed-scene position.
They can even be constrained to other objects so that one object's position can be glued down to a certain location on another object, like a shirt on a hanger or a hook on a fishing line. There are all kinds of different things that can be configured. One of the other really cool things about Reactor is how quick it generates its previews--its speed in making and displaying as calculations in other words. While some 3D software simulation engines require lengthy calculation times before your results can be viewed and evaluated, Reactor's Preview window works in near real-time speed--meaning that feedback is almost immediate, which saves not just time but makes the entire process much more interactive.
Let's see how our simulation looks. Back on the Reactor toolbar on the left, a little further down, you will find a button that reads Preview Animation. Go ahead and click on that. This brings up Reactor's Preview window. To play things back, we simply have to type the P key on our keyboard. To reset the action, you type R. Then to play again, you'll tap the P key. When you're happy with your results, you can then commit to what you've created by generating the actual keyframes that bakes everything together.
That, like almost everything else in Reactor, can be done from several locations in the interface. For our demonstration here though, we'll continue hanging out on the toolbar on the left. Down at the bottom, we'll click on Create Animation. After a short calculation, our keyframes have been made. We can then play the Timeline to see the actual animation. You can also at this point, with those keyframes having been made, scrub the Timeline back and forth to review your work.
So, that will give you a quick overview as to how the Reactor workflow operates. Coming up in the next video, we'll take a look at where exactly in the 3ds interface the Reactor controls and commands are found.
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