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As with all aspects of CG work, the effort we put into the preproduction and planning stages of a simulation projects can either make or break the shot or shots that we're working on. Ideally, once we receive the scene with which we will be working--be that the final version or indeed a low-res stand- in--we will want to examine the script or brief and the scene itself so as to determine what simulation effects are going to be required or maybe even possible. During this part of the process it would probably be a good idea for us to be making as many notes as possible, including of course noting down some ideas regarding the tools we could possibly use to accomplish the desired end result.
In our case, as you can see, we have a fairly well-developed version of a scene that could easily be brought up to final render standard. So we're in fact ready now to plan out, maybe even start to previz, the specific effects required for our shot. Let's imagine the premise here is that our biped customer has come to watch our ball launchers knock down the stacks of cans. What we need to do now is figure out which objects in the scene will need to be a part of the simulation, so we'll need rigid body modifiers adding to them, as well as perhaps noting down which rigid body type we think will work best in each instance.
The first thing we want to do is just hit the C key on our keyboard to bring up our Select Camera dialog. Once we have that, we can switch over to our Launches camera for a closer view of the launcher geometry. Now, if I just press play down in our animation controls, you can see we have a very simple animation on the launcher geometry. The idea is that these animated discs will propel each of the colored spheres out of the launcher tubes, across the open space, and into our waiting stacks of cans.
With an understanding of what is required then, it seems pretty clear that our animated discs, the spheres in the holding rack, the holding rack itself, and of course the launcher geometry will all need to be a part of the simulation, so we'll need rigid body modifiers applying to them. Which rigid body type should we use? Well, as our launcher tubes really only need to hold our shoot or cannonballs before they're launched, we can safely assume that these really only need to be set up as static rigid bodies.
As noted in chapter 1, static rigid bodies can have dynamic objects such as our spheres bump into and bounce off them, but the static rigid body itself won't react in any way. That makes it perfect for what we need here. In fact, the static rigid body type could also be used for our holding racks as well, so let's makes a note of those facts. The balls or sphere themselves of course are going to be doing the both of the interesting work inside the simulation, as they're going to be launched into the air and hopefully collide with our stacks of cans.
This means they really will need to be set up as dynamic objects within the simulation-- that is, ones they can collide with and affect and be affected by other dynamic rigid bodies in the scene. We also have the animated discs. Now the fact that these are animated pieces of geometry means we only really have one rigid body choice available to us, which would be to set these up as kinematic rigid bodies. This means they will be able to interact with and affect the dynamic objects in the simulation, but without actually being affected in any way themselves. Of course, we will also need to devise some method for dropping each of the balls into the launcher tubes.
Probably the best thing here would be to use a feature of the kinematic rigid body type that allows us to specify a frame in the animation at which a kinematic rigid body becomes a dynamic one. This would mean we could very specifically time each of the ball drops into the launcher tubes. So with our launcher assemblies taken care of, let's once again use the C keyboard shortcut and bring up over Select Camera dialog, and this time we'll choose Target camera option. From here we can get a good view of where our launched objects are our launched phase will be traveling to in the scene.
As we want our balls to collide with and knock our stacks of cans over and because of course we want the cans to interact with one another, it doesn't take much to work out that once again we'll need to make use of the dynamic rigid body type for our can stacks. Once the cans have been knocked down of course we'll want those and the launch spheres to collide with the shelves, the concession stand body itself, and probably even a ground object. So once again, making use off the static rigid body option would seem sensible.
Having taken then the time to figure out what we need in terms of setup so as to create the desired simulation effects in our shot, we are ready to move on in our next video to setting up or applying the rigid body modifier to our geometry and then setting up some of the basic parameters that our simulation objects will need.
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