Add damping support + demos.

7 files changed, 140 insertions, 0 deletions

diff --git a/examples2d/all_examples2.rs b/examples2d/all_examples2.rs
index 052d6cc..92606d8 100644
--- a/examples2d/all_examples2.rs
+++ b/examples2d/all_examples2.rs
@@ -12,6 +12,7 @@ use std::cmp::Ordering;
 
 mod add_remove2;
 mod collision_groups2;
+mod damping2;
 mod debug_box_ball2;
 mod heightfield2;
 mod joints2;
@@ -55,6 +56,7 @@ pub fn main() {
     let mut builders: Vec<(_, fn(&mut Testbed))> = vec![
         ("Add remove", add_remove2::init_world),
         ("Collision groups", collision_groups2::init_world),
+        ("Damping", damping2::init_world),
         ("Heightfield", heightfield2::init_world),
         ("Joints", joints2::init_world),
         ("Platform", platform2::init_world),
diff --git a/examples2d/damping2.rs b/examples2d/damping2.rs
new file mode 100644
index 0000000..43ca2b6
--- /dev/null
+++ b/examples2d/damping2.rs
@@ -0,0 +1,45 @@
+use na::{Point2, Vector2};
+use rapier2d::dynamics::{JointSet, RigidBodyBuilder, RigidBodySet};
+use rapier2d::geometry::{ColliderBuilder, ColliderSet};
+use rapier_testbed2d::Testbed;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let joints = JointSet::new();
+
+    /*
+     * Create the balls
+     */
+    let num = 10;
+    let rad = 0.2;
+
+    let subdiv = 1.0 / (num as f32);
+
+    for i in 0usize..num {
+        let (x, y) = (i as f32 * subdiv * std::f32::consts::PI * 2.0).sin_cos();
+
+        // Build the rigid body.
+        let rb = RigidBodyBuilder::new_dynamic()
+            .translation(x, y)
+            .linvel(x * 10.0, y * 10.0)
+            .angvel(100.0)
+            .linear_damping((i + 1) as f32 * subdiv * 10.0)
+            .angular_damping((num - i) as f32 * subdiv * 10.0)
+            .build();
+        let rb_handle = bodies.insert(rb);
+
+        // Build the collider.
+        let co = ColliderBuilder::cuboid(rad, rad).build();
+        colliders.insert(co, rb_handle, &mut bodies);
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world_with_gravity(bodies, colliders, joints, Vector2::zeros());
+    testbed.look_at(Point2::new(3.0, 2.0), 50.0);
+}
diff --git a/examples3d/all_examples3.rs b/examples3d/all_examples3.rs
index 2196605..9c1dffc 100644
--- a/examples3d/all_examples3.rs
+++ b/examples3d/all_examples3.rs
@@ -13,6 +13,7 @@ use std::cmp::Ordering;
 mod add_remove3;
 mod collision_groups3;
 mod compound3;
+mod damping3;
 mod debug_boxes3;
 mod debug_cylinder3;
 mod debug_triangle3;
@@ -69,6 +70,7 @@ pub fn main() {
         ("Primitives", primitives3::init_world),
         ("Collision groups", collision_groups3::init_world),
         ("Compound", compound3::init_world),
+        ("Damping", damping3::init_world),
         ("Domino", domino3::init_world),
         ("Heightfield", heightfield3::init_world),
         ("Joints", joints3::init_world),
diff --git a/examples3d/damping3.rs b/examples3d/damping3.rs
new file mode 100644
index 0000000..e055d8e
--- /dev/null
+++ b/examples3d/damping3.rs
@@ -0,0 +1,45 @@
+use na::{Point3, Vector3};
+use rapier3d::dynamics::{JointSet, RigidBodyBuilder, RigidBodySet};
+use rapier3d::geometry::{ColliderBuilder, ColliderSet};
+use rapier_testbed3d::Testbed;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let joints = JointSet::new();
+
+    /*
+     * Create the balls
+     */
+    let num = 10;
+    let rad = 0.2;
+
+    let subdiv = 1.0 / (num as f32);
+
+    for i in 0usize..num {
+        let (x, y) = (i as f32 * subdiv * std::f32::consts::PI * 2.0).sin_cos();
+
+        // Build the rigid body.
+        let rb = RigidBodyBuilder::new_dynamic()
+            .translation(x, y, 0.0)
+            .linvel(x * 10.0, y * 10.0, 0.0)
+            .angvel(Vector3::z() * 100.0)
+            .linear_damping((i + 1) as f32 * subdiv * 10.0)
+            .angular_damping((num - i) as f32 * subdiv * 10.0)
+            .build();
+        let rb_handle = bodies.insert(rb);
+
+        // Build the collider.
+        let co = ColliderBuilder::cuboid(rad, rad, rad).build();
+        colliders.insert(co, rb_handle, &mut bodies);
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world_with_gravity(bodies, colliders, joints, Vector3::zeros());
+    testbed.look_at(Point3::new(2.0, 2.5, 20.0), Point3::new(2.0, 2.5, 0.0));
+}
diff --git a/src/dynamics/rigid_body.rs b/src/dynamics/rigid_body.rs
index d3bd8d7..4aaa474 100644
--- a/src/dynamics/rigid_body.rs
+++ b/src/dynamics/rigid_body.rs
@@ -42,6 +42,10 @@ pub struct RigidBody {
     pub linvel: Vector<f32>,
     /// The angular velocity of the rigid-body.
     pub angvel: AngVector<f32>,
+    /// Damping factor for gradually slowing down the translational motion of the rigid-body.
+    pub linear_damping: f32,
+    /// Damping factor for gradually slowing down the angular motion of the rigid-body.
+    pub angular_damping: f32,
     pub(crate) linacc: Vector<f32>,
     pub(crate) angacc: AngVector<f32>,
     pub(crate) colliders: Vec<ColliderHandle>,
@@ -70,6 +74,8 @@ impl RigidBody {
             angvel: na::zero(),
             linacc: Vector::zeros(),
             angacc: na::zero(),
+            linear_damping: 0.0,
+            angular_damping: 0.0,
             colliders: Vec::new(),
             activation: ActivationStatus::new_active(),
             joint_graph_index: InteractionGraph::<()>::invalid_graph_index(),
@@ -218,6 +224,10 @@ impl RigidBody {
     }
 
     pub(crate) fn integrate(&mut self, dt: f32) {
+        // TODO: do we want to apply damping before or after the velocity integration?
+        self.linvel *= 1.0 / (1.0 + dt * self.linear_damping);
+        self.angvel *= 1.0 / (1.0 + dt * self.angular_damping);
+
         self.position = self.integrate_velocity(dt) * self.position;
     }
 
@@ -338,6 +348,8 @@ pub struct RigidBodyBuilder {
     position: Isometry<f32>,
     linvel: Vector<f32>,
     angvel: AngVector<f32>,
+    linear_damping: f32,
+    angular_damping: f32,
     body_status: BodyStatus,
     mass_properties: MassProperties,
     can_sleep: bool,
@@ -351,6 +363,8 @@ impl RigidBodyBuilder {
             position: Isometry::identity(),
             linvel: Vector::zeros(),
             angvel: na::zero(),
+            linear_damping: 0.0,
+            angular_damping: 0.0,
             body_status,
             mass_properties: MassProperties::zero(),
             can_sleep: true,
@@ -438,6 +452,24 @@ impl RigidBodyBuilder {
         self
     }
 
+    /// Sets the damping factor for the linear part of the rigid-body motion.
+    ///
+    /// The higher the linear damping factor is, the more quickly the rigid-body
+    /// will slow-down its translational movement.
+    pub fn linear_damping(mut self, factor: f32) -> Self {
+        self.linear_damping = factor;
+        self
+    }
+
+    /// Sets the damping factor for the angular part of the rigid-body motion.
+    ///
+    /// The higher the angular damping factor is, the more quickly the rigid-body
+    /// will slow-down its rotational movement.
+    pub fn angular_damping(mut self, factor: f32) -> Self {
+        self.angular_damping = factor;
+        self
+    }
+
     /// Sets the initial linear velocity of the rigid-body to be created.
     #[cfg(feature = "dim2")]
     pub fn linvel(mut self, x: f32, y: f32) -> Self {
@@ -474,6 +506,8 @@ impl RigidBodyBuilder {
         rb.body_status = self.body_status;
         rb.user_data = self.user_data;
         rb.mass_properties = self.mass_properties;
+        rb.linear_damping = self.linear_damping;
+        rb.angular_damping = self.angular_damping;
 
         if !self.can_sleep {
             rb.activation.threshold = -1.0;
diff --git a/src_testbed/engine.rs b/src_testbed/engine.rs
index 1bafdb6..52b9ca9 100644
--- a/src_testbed/engine.rs
+++ b/src_testbed/engine.rs
@@ -152,6 +152,7 @@ impl GraphicsManager {
         self.f2sn.clear();
         #[cfg(feature = "fluids")]
         self.boundary2sn.clear();
+        self.c2color.clear();
         self.b2color.clear();
         self.b2wireframe.clear();
         self.rand = Pcg32::seed_from_u64(0);
diff --git a/src_testbed/testbed.rs b/src_testbed/testbed.rs
index 7160b3b..66b5953 100644
--- a/src_testbed/testbed.rs
+++ b/src_testbed/testbed.rs
@@ -405,8 +405,19 @@ impl Testbed {
     }
 
     pub fn set_world(&mut self, bodies: RigidBodySet, colliders: ColliderSet, joints: JointSet) {
+        self.set_world_with_gravity(bodies, colliders, joints, Vector::y() * -9.81)
+    }
+
+    pub fn set_world_with_gravity(
+        &mut self,
+        bodies: RigidBodySet,
+        colliders: ColliderSet,
+        joints: JointSet,
+        gravity: Vector<f32>,
+    ) {
         println!("Num bodies: {}", bodies.len());
         println!("Num joints: {}", joints.len());
+        self.gravity = gravity;
         self.physics.bodies = bodies;
         self.physics.colliders = colliders;
         self.physics.joints = joints;