Module bevy_picking_core::backend

This module provides a simple interface for implementing a picking backend.

Don’t be dissuaded by terminology like “backend”; the idea is dead simple. bevy_picking_core will tell you where pointers are, all you have to do is send an event if the pointers are hitting something. That’s it. The rest of this documentation explains the requirements in more detail.

Because bevy_picking_core is very loosely coupled with its backends, you can mix and match as many backends as you want. For example, You could use the rapier backend to raycast against physics objects, a picking shader backend to pick non-physics meshes, and the bevy_ui backend for your UI. The PointerHitss produced by these various backends will be combined, sorted, and used as a homogeneous input for the picking systems that consume these events.

Implementation

• A picking backend only has one job: read PointerLocation components and produce PointerHits events. In plain English, a backend is provided the location of pointers, and is asked to provide a list of entities under those pointers.

• The PointerHits events produced by a backend do not need to be sorted or filtered, all that is needed is an unordered list of entities and their HitData.

• Backends do not need to consider the Pickable component, though they may use it for optimization purposes. For example, a backend that traverses a spatial hierarchy may want to early exit if it intersects an entity that blocks lower entities from being picked.

Raycasting Backends

Backends that require a ray to cast into the scene should use ray::RayMap. This automatically constructs rays in world space for all cameras and pointers, handling details like viewports and DPI for you.

Modules

• prelude
  Common imports for implementing a picking backend.
• ray
  Types and systems for constructing rays from cameras and pointers.

Structs

• HitData
  Holds data from a successful pointer hit test. See HitData::depth for important details.
• PointerHits
  An event produced by a picking backend after it has run its hit tests, describing the entities under a pointer.