Collisions & Physics: Hello Physics Simulation Component
We can use this component to create localized physics rules.
Overview
The first thing to know is that this component should always be added to parent of the physics entities. Adding it directly to an entity with other physics components may result in some odd behaviors. Let’s load a scene from Reality Composer Pro, then add this component to the root entity.
guard let scene = try? await Entity(named: "PhysicsSimulationBasics", in: realityKitContentBundle) else { return }
content.add(scene)
if let root = scene.findEntity(named: "Root") {
var simulation = PhysicsSimulationComponent()
simulation.gravity = [0, 9.81, 0]
root.components.set(simulation)
}This scene has two static physics objects and a blue sphere with dynamic physics.
Let’s look at an example of customizing gravity. By default, gravity in RealityKit is defined as -9.81 on the y axis. This is an approximation of earth gravity. If we invert the number, dynamic bodies will “fall” up.
var simulation = PhysicsSimulationComponent()
simulation.gravity = [0, 9.81, 0] // gravity is now up!
root.components.set(simulation)Playing with gravity can bring a lot of fun and delight to users. This component has a few more features.
- clock: we can define custom clocks, for example if we need to evaluate physics more or less often
- collision options: we can tailor how collisions are reported
- solver options: we can adjust the number of iterations for solving physics. This can be helpful if your scene has very fast moving objects.
This component is required for some other features, such as Physics Joints.
Video Demo
Example Code
struct Example062: View {
@State var gravity: SIMD3<Float> = [0, 9.8, 0]
var body: some View {
RealityView { content in
guard let scene = try? await Entity(named: "PhysicsSimulationBasics", in: realityKitContentBundle) else { return }
content.add(scene)
scene.position.y = -0.4
if let root = scene.findEntity(named: "Root") {
var simulation = PhysicsSimulationComponent()
simulation.gravity = gravity
root.components.set(simulation)
}
} update: { content in
// Update the simulation gravity when the value changes
var simulation = PhysicsSimulationComponent()
simulation.gravity = gravity
content.entities.first?.findEntity(named: "Root")?.components.set(simulation)
}
.ornament(attachmentAnchor: .scene(.trailingFront), ornament: {
VStack {
Button(action: {
gravity = [0, 9.81, 0]
}, label: {
Label("Up Strong", systemImage: "chevron.up.2")
.frame(maxWidth: .infinity, alignment: .leading)
})
Button(action: {
gravity = [0, 1, 0]
}, label: {
Label("Up Weak", systemImage: "chevron.up")
.frame(maxWidth: .infinity, alignment: .leading)
})
Button(action: {
gravity = [0, -1, 0]
}, label: {
Label("Down Weak", systemImage: "chevron.down")
.frame(maxWidth: .infinity, alignment: .leading)
})
Button(action: {
gravity = [0, -9.81, 0]
}, label: {
Label("Down Strong", systemImage: "chevron.down.2")
.frame(maxWidth: .infinity, alignment: .leading)
})
}
.padding()
.glassBackgroundEffect()
})
}
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