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Fix interpolation of kinematic character controllers #463

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Fix interpolation of kinematic character controllers #463

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10 changes: 10 additions & 0 deletions src/dynamics/rigid_body.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -566,6 +566,16 @@ pub struct TransformInterpolation {
}

impl TransformInterpolation {
/// Skips interpolation, effectively causing the body to immediately teleport to its current
/// transform.
///
/// This is most useful with kinematic character controllers, which always interpolate and do
/// not perform transform change detection like rigid bodies do.
pub fn teleport(&mut self) {
self.start = None;
self.end = None;
}

/// Interpolates between the start and end positions with `t` in the range `[0..1]`.
pub fn lerp_slerp(&self, t: f32) -> Option<Isometry<f32>> {
if let (Some(start), Some(end)) = (self.start, self.end) {
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4 changes: 2 additions & 2 deletions src/plugin/context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -249,8 +249,8 @@ impl RapierContext {
// Update the previous state transforms
for (handle, mut interpolation) in interpolation_query.iter_mut() {
if let Some(body) = self.bodies.get(handle.0) {
interpolation.start = Some(*body.position());
interpolation.end = None;
interpolation.start = interpolation.end;
interpolation.end = Some(*body.position());
Comment on lines -252 to +253
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From what I understanded of bevy_rapier's code this change is not valid, because this system execute whole Rapier's subupdates (I stick to name convention from #464), and this code block is executed only for last subupdate. This stores a value from previous subupdate, and next sets final subupdate position as end in lerp system:

bevy_rapier/src/plugin/systems.rs

Lines 554 to 556 in c6bcce4

if interpolation.end.is_none() {
interpolation.end = Some(*rb.position());
}

Maybe in case where you have only a one subupdate a code what are you change is invalid, but I must think about this. But otherwise in my opinion code which is writed earlier is correct.

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After implementation expected behavior from #464 I do not know how lerp should looks. When delta time of FixedUpdate is greater than delta time of Update @liquidev's lerp works good, but in situation when it is lower earlier lerp works good. For equals I do not know this at this time. Someone should investigate this.

}
}
}
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37 changes: 22 additions & 15 deletions src/plugin/systems.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -280,6 +280,7 @@ pub fn apply_rigid_body_user_changes(
&RapierRigidBodyHandle,
&GlobalTransform,
Option<&mut TransformInterpolation>,
Option<&KinematicCharacterController>,
),
Changed<GlobalTransform>,
>,
Expand Down Expand Up @@ -354,24 +355,30 @@ pub fn apply_rigid_body_user_changes(
}
};

for (handle, global_transform, mut interpolation) in changed_transforms.iter_mut() {
for (handle, global_transform, mut interpolation, kinematic_character_controller) in
changed_transforms.iter_mut()
{
// Use an Option<bool> to avoid running the check twice.
let mut transform_changed = None;

if let Some(interpolation) = interpolation.as_deref_mut() {
transform_changed = transform_changed.or_else(|| {
Some(transform_changed_fn(
&handle.0,
global_transform,
&context.last_body_transform_set,
))
});

if transform_changed == Some(true) {
// Reset the interpolation so we don’t overwrite
// the user’s input.
interpolation.start = None;
interpolation.end = None;
// Kinematic character controllers update outside of our tick loop, and therefore we must
// exclude them from interpolation.
if kinematic_character_controller.is_none() {
if let Some(interpolation) = interpolation.as_deref_mut() {
transform_changed = transform_changed.or_else(|| {
Some(transform_changed_fn(
&handle.0,
global_transform,
&context.last_body_transform_set,
))
});

if transform_changed == Some(true) {
// Reset the interpolation so we don’t overwrite
// the user’s input.
interpolation.start = None;
interpolation.end = None;
}
}
}

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