Sensors and mass properties #355
Conversation
- Default density and mass 0.0 for sensors - Ignore sensors when updating parents' mass properties
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Hi, I do agree we should change this. I looked into it a bit, and it seems like the sensor equivalents in Godot (Area2D/Area3D) and Unity (trigger property) also don't contribute to the mass properties of the rigid body. I think the semantics we should go for are that sensors don't affect physics at all, and are only for detecting intersections. The way I would do this is slightly different from this PR though:
I think this could be implemented robustly in Bevy 0.14 using component lifecycle hooks or observers. Notably different from this PR, I would not make the default Do you mind if I adopt this and implement it for the upcoming Bevy 0.14 update with lifecycle hooks (or observers)? I can still add you as a co-author :) |
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All that sounds good. Thanks for taking a look. |
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Closing in favor of #381 :) |
# Objective Similar to #355 by @yrns, but without special casing `ColliderDensity` defaults, and implemented with observers. Sensor colliders currently contribute to the mass properties of rigid bodies. This differs from most peoples' expectations, and is also different from many existing engines such as Godot and Unity. Sensor colliders should have no impact on the physics simulation. ## Solution - When the `Sensor` component is added to an entity, remove the collider's contribution on the rigid body's mass properties. - When the `Sensor` component is removed from an entity, add the collider's mass properties to the rigid body's mass properties. ## Testing There is a test to make sure that the mass properties of a rigid body are updated accordingly when the `Sensor` component is first added and then removed from a collider. --- ## Migration Guide Colliders with the `Sensor` component no longer contribute to the mass properties of rigid bodies. You can add mass for them by adding another collider that is *not* a sensor, or by manually adding mass properties with the `MassPropertiesBundle` or its components. Additionally, the mass properties of `Sensor` colliders are no longer updated automatically, unless the `Sensor` component is removed. --------- Co-authored-by: Al McElrath <hello@yrns.org>
Objective
I was surprised to find that a sensor added as a child of a dynamic body affected the parent's behavior. Even with the density set to zero the difference was noticeable.
Solution
and/or:
Maybe instead of adding a special case for sensors (which would be a breaking change), a note should be added to the sensor documentation indicating you need to set the mass properties to zero if you don't want to affect any parents?
Changelog
tbd
Migration Guide
tbd