Using Blender Drivers

Blender Drivers are a way to control values of properties by means of a function, or a mathematical expression. Drivers can be used to power values in Bevy components, such as using the width, height, and depth of a cube to power an Avian Cuboid Collider's size. Then when resizing the cube, the collider's values track to the new values.

Driving Collider fields

We'll be using a Blender Object's dimensions in this example. Specifically the default cube's. More data fields can be found in the docs

Note

We start having already inserted a Avian ColliderConstructor::Cuboid Component. Read Inserting Components if you need to learn how to do that

Add a Driver

Right click on a Component value (we're using the x_length) and select Add Driver

add driver menu

The Driver form will show. Drivers can be as simple as a single property to as complex as arbitrary python.

add driver form

We'll select Single Property

add driver single property field

This shows a new form

single property form

We'll select the default cube as our Object

add driver select object

Then we'll set the Path for our property

add driver selected cube object

We'll use dimensions to get the x, y, and z length (aka: width, height, and depth).

Important

Blenders dimensions are Y-up, so dimensions[0] is x, dimensions[1] is y, and dimensions[2] is z.

In Bevy, Z is up, so we need to map Blender's coordinates to the values our components expect in Bevy:

x -> x_length
y -> z_length
z -> y_length

driver path usinge dimensions

Repeat for all three values

If you repeat these steps for all three values, all three will be controlled by their respective dimensions.

three drivers for three values

Scaling the Cube

Switch into Edit Mode (use Tab or the top-left menu)

switch into edit mode

Scale the cube up (hit s)

Scaling the cube in edit mode

Watch as the values grow as the cube scales. This is Drivers.

The values that are driven into the component values will be exported with the glTF export.