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With our Rigid Body Collection now as the official address for all of our scene objects that will be running through our simulation, we can now proceed with a preview to see how things are turning out. We'll do that using the Breaking Glass04 file that we saved up at the end of our last video. Before we run any previews, let's take a moment and talk about the options that we have as far as choosing a physics engine for our simulation. In our first chapter in the video on choosing the correct physics engine we established the fact that when running a rigid body simulation that either Havok simulation engine 1 or 3 was up for the task.
After doing little experimentation, I've concluded that for this particular project the Havok 1 engine is going to give us the most accurate and most reliable results. For that reason, even though the manuals will tell you that the newer Havok 3 engine is both faster and usually yields a more accurate simulation when running rigid bodies, we're going to be sticking with the older original Havok 1 physics engine solution here. Let's do a quick preview and see how things look. Using the Reactor toolbar we have positioned on the left-hand side of our screen, we'll drop down to the bottom of our icons, choosing Preview Animation.
Before running this thing through, remember your mouse options. You can use the left mouse button to orbit. You can use the middle mouse button to both pan and zoom. To get things rolling, we'll type P, for Play. Let's watch that again, by first resetting with R, then P again.
About three-quarters the way down, let's open up the Havok 1 World tab. Then for our Collision Tolerance, let's lower that to about 2. You may recall the Collision Tolerance controls how close or how far apart neighboring objects need to be in order to detect or start feeling each other. Let's see if that change makes any difference. This time to run the preview, we'll stay on the right-hand side, opening up the Preview & Animation tab. From here, we'll simply click on Preview in Window.
Let's type P again. Let's try moving our rock a little and see how that changes the outcome. We'll close the window, then make that positional move in the front view. Once we've done that, we'll preview again. Positioned now a little more off to the side, you can see how the rock is having more of an impact on the frame.
Let's close the Preview Window, taking our rock back to its original position. Another accuracy tweak we might try of getting of unpredictable results with our sim is experimenting with increasing the number of Substeps. Let's try that. Back in the Utilities panel on the right, that setting is a little bit above the Preview button. Let's take our Substeps/Key to 15. This will increase the number of calculations made at each keyframe. With that number in place, we'll then preview again.
Not much of a change there, with only a slight difference--probably not worth the added calculation time. Let's take that Substeps/Key value back to the default number of 10. Now I don't know if you noticed down on the Havok 1 World section, but we also have controls for gravity. These are kind of fun to play with. Let's take the Z gravity to -100, and we'll then run another sim.
So here you find the following pieces falling not quite so aggressively. Now, if you are wanting no gravitational influence, we could take that Z value to 0. Let's try that. Run things through again and you can see the difference there. The Gravity controls can even be set in a positive direction. Let's close the Preview window, setting gravity in the Z direction to 300, and once that number is in place previewing again.
Take a look at that. This time instead of the pieces falling downwards, they are actually spiraling up. Why don't we take the Z-based gravity back to -300, and we'll try X at a thousand. This should have the impact of pulling or shattering objects to the side. Let's try that. So there you go, the spinning pieces now not just falling downward but also being pushed fairly aggressively to the right. Running a sim, you notice that you're breaking apart objects need a little extra glue applied to them in order to hold together just a little bit longer before they start going in their own directions.
You can apply something called a fracture to those breaking-apart surfaces. We'll take a look at how that's done in the next video. Let's go ahead and save our file up as Breaking Glass05, and we'll take it with us.
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