Entities & components

Entities are the objects in your scenes. Components hold their data, such as meshes, physics bodies and scripts.

Making an entity

An entity is a node you can attach components to, so it lives in the scene tree like any other node. Make one, then add it to your scene:

Handle<Entity> crate = MakeHandle<Entity>();
crate->SetName(NAME("Crate"));

scene->GetRoot()->AddChild(crate);

Once it's in a scene, it automatically gets a TransformComponent, a BoundingBoxComponent and a VisibilityStateComponent.

Adding components

Components are plain structs:

MeshComponent meshComponent;
meshComponent.mesh = crateMesh;
meshComponent.material = crateMaterial;

crate->AddComponent<MeshComponent>(meshComponent);
crate->SetLocalBounds(crateMesh->GetAABB());

The last line sets the entity's bounds, which culling uses. The other component methods:

• GetComponent<T>() returns a reference. The component must exist.
• TryGetComponent<T>() returns a pointer, or nullptr if it's missing.
• HasComponent<T>() checks for one.
• RemoveComponent<T>() removes it.

An entity can only have one of each component type. Adding a second will trip an assert.

Transforms

Entities are nodes, so they've got a transform. The Local setters are relative to the parent, the World ones aren't:

crate->SetLocalTranslation(Vec3f(0.0f, 2.0f, 0.0f));
crate->SetWorldScale(Vec3f(2.0f, 2.0f, 2.0f));
crate->Translate(Vec3f(1.0f, 0.0f, 0.0f)); // relative to where it is now

To look a node up by name: scene->FindNodeByName("Crate"_sh).

Built-in components

Common ones:

Making your own

Declare a struct with HYP_STRUCT(Component), and mark up the fields you want saved and shown in the editor:

HYP_STRUCT(Component, Label = "Health Component")
struct HealthComponent
{
    HYP_STRUCT_BODY(HealthComponent);

    HYP_FIELD(Property = "Health", Serialize, Editor)
    float health = 100.0f;
};

Then include the generated file in your .cpp:

#include <HealthComponent.generated.inl>

Re-run CodeGen (reconfiguring CMake runs it) to register the component. To process it every frame, write a system.