Poser Basics: What is Bullet Physics?

Oct 06, 2021 at 10:00 am by Michelle Willard

Poser Basics: What is Bullet Physics?

Bullet Physics is a third-party developed, open-source software that calculates the interactions between rigid (or hard) and soft bodies in real-time.

Mainly developed by Erwin Coumans, Bullet Physics has been used for years in video games and visual effects in movies and television. In fact, Coumans won a Scientific and Technical Academy Award for his work on Bullet.

Bullet Physics is used in PlayStation and has been integrated into Houdini, Cinema 4D, LightWave 3D, and Blender, among others. It was integrated into Poser in 2013 with Poser 10.

Bullet Physics differs from dynamic cloth in Poser, which is created in the Cloth Room. You can learn more about using dynamics here.

How to Use Bullet Physics

You can use Bullet Physics to inflate and deflate tires, make cloth realistically drape, and even make people walk. It can be used on any object that you want to jiggle or bend.

Poser's Physics Simulation palette allows you to incorporate Bullet physics into your Poser animations and renders. To open the palette, choose Window > Bullet Physics Controls. From here, you create a simulation.

First, click the New button to create a new simulation on the Physics Simulation palette.

The Simulation Name dialog will prompt you to enter a name for the simulation. After you enter the name, click OK to create the simulation.

To limit the number of frames in your simulation, enter the starting and ending frames of the desired frame range in the Start Frame and End Frame fields.

Do not select "Live Simulation" until you are ready.

Next, select the objects. This will open the "Select Objects" dialog box with three options displayed in tabs:

• Choreographed is used to define stationary or animated objects in your scene that the dynamic objects will collide with.
• Rigid Dynamic is used for hard-bodied objects that will have physics applied to them. These objects will maintain their shape when they interact with other objects in the scene.
• Soft Dynamic is used for soft-bodied objects that will have physics applied to them. The shape of these objects are affected by collision with other objects in the scene. In Bullet, soft bodies includes cloth, rope and deformable objects. 

As you switch from one tab to the next, you place a check beside each of the objects in your scene that you want to designate as that object type and therefore be impacted by the Bullet Physics engine. For example, under the "Soft Dynamic" tab, you can select any cloth to "clothify" it, or make it soft so that it drapes over rigid objects, like the human figure in your scene. You can make human figures soft if you want the physics engine applied to the figure.

Most importantly, you need to set your collisions. If you don't, then the objects will slide through each other and create poke throughs. You will do this under the Choreographed tab by selecting the parts of the Rigid object you want to apply physics to.

At this point, the Live Simulation option is helpful to preview how your simulation settings affect the physics objects in your scene. This allows you to see in real-time how the objects respond to gravity, motion, and collision with other objects.

To fine tune your physics, use the Physics Simulation palette. From here, you can select the object's properties that need adjustments. Constraints allow you to configure your physics objects using one of three different ways:

• Self Constraint: Defines how the object responds to physics calculations. Each object can have only one self-constraint. After you add a self-constraint, all vertices are initially set to fully dynamic. Use the vertex painting tools to constrain the vertices that you paint.
• Animated Constraint: Allows you to use a handle to animate an object. The handle can be assigned as a child of any other object in your scene, or animated in any way you choose. The handle serves as a transform that you can move things around with. The handle will pull on the vertices that you paint.
• Object Constraint: Constrains one object to another so that they move together. You use a handle to define the point at which the two objects are supposed to connect to each other, and tries to keep both objects connected at that point.

Once you have all your options set, you can save your physics objects. You can save them to the Library with their settings intact. This allows you to save items that bounce, or jiggle, or use specific hard or soft-bodied settings.

After a Bullet Physics object is saved to the Library, you will need to re-simulate the object(s) when you load them into your scene. If an object is shared between two or more simulations, it will only save the current simulation that was selected when you saved the object to the Library.

For a more detailed explanation about how to use Bullet Physics and cloth, watch the tutorial below. It was created for Poser Pro 2014, but the explanations still apply.



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