feat: implement new "small-steps" solver + joint improvements

examples3d/debug_cube_high_mass_ratio3.rs

@@ -0,0 +1,96 @@
+use rapier3d::prelude::*;
+use rapier_testbed3d::Testbed;
+
+pub fn init_world(testbed: &mut Testbed) {
+    /*
+     * World
+     */
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let impulse_joints = ImpulseJointSet::new();
+    let multibody_joints = MultibodyJointSet::new();
+
+    let num_levels = 4;
+    let stick_len = 2.0;
+    let stick_rad = 0.2;
+
+    /*
+     * Floor.
+     */
+    let floor_body =
+        RigidBodyBuilder::fixed().translation(vector![0.0, -stick_len - stick_rad, 0.0]);
+    let floor_handle = bodies.insert(floor_body);
+    let floor_cube = ColliderBuilder::cuboid(stick_len, stick_len, stick_len);
+    colliders.insert_with_parent(floor_cube, floor_handle, &mut bodies);
+
+    /*
+     * Create a stack of capsule with a very heavy cube on top.
+     */
+    for i in 0..num_levels {
+        let fi = i as f32;
+
+        let body = RigidBodyBuilder::dynamic().translation(vector![
+            0.0,
+            fi * stick_rad * 4.0,
+            -(stick_len / 2.0 - stick_rad)
+        ]);
+        let handle = bodies.insert(body);
+        let capsule = ColliderBuilder::cuboid(stick_len / 2.0, stick_rad, stick_rad);
+        colliders.insert_with_parent(capsule, handle, &mut bodies);
+
+        let body = RigidBodyBuilder::dynamic().translation(vector![
+            0.0,
+            fi * stick_rad * 4.0,
+            (stick_len / 2.0 - stick_rad)
+        ]);
+        let handle = bodies.insert(body);
+        let capsule = ColliderBuilder::cuboid(stick_len / 2.0, stick_rad, stick_rad);
+        colliders.insert_with_parent(capsule, handle, &mut bodies);
+
+        let body = RigidBodyBuilder::dynamic().translation(vector![
+            -(stick_len / 2.0 - stick_rad),
+            (fi + 0.5) * stick_rad * 4.0,
+            0.0
+        ]);
+        let handle = bodies.insert(body);
+        let capsule = ColliderBuilder::cuboid(stick_rad, stick_rad, stick_len / 2.0);
+        colliders.insert_with_parent(capsule, handle, &mut bodies);
+
+        let body = RigidBodyBuilder::dynamic().translation(vector![
+            (stick_len / 2.0 - stick_rad),
+            (fi + 0.5) * stick_rad * 4.0,
+            0.0
+        ]);
+        let handle = bodies.insert(body);
+        let capsule = ColliderBuilder::cuboid(stick_rad, stick_rad, stick_len / 2.0);
+        colliders.insert_with_parent(capsule, handle, &mut bodies);
+    }
+
+    /*
+     * Big cube on top.
+     */
+    let cube_len = stick_len * 2.0;
+    let floor_body = RigidBodyBuilder::dynamic()
+        .translation(vector![
+            0.0,
+            cube_len / 2.0 + (num_levels as f32 - 0.25) * stick_rad * 4.0,
+            0.0
+        ])
+        .additional_solver_iterations(36);
+    let floor_handle = bodies.insert(floor_body);
+    let floor_cube = ColliderBuilder::cuboid(cube_len / 2.0, cube_len / 2.0, cube_len / 2.0);
+    colliders.insert_with_parent(floor_cube, floor_handle, &mut bodies);
+
+    let small_mass =
+        MassProperties::from_cuboid(1.0, vector![stick_rad, stick_rad, stick_len / 2.0]).mass();
+    let big_mass =
+        MassProperties::from_cuboid(1.0, vector![cube_len / 2.0, cube_len / 2.0, cube_len / 2.0])
+            .mass();
+    println!("debug_cube_high_mass_ratio3: small stick mass: {small_mass}, big cube mass: {big_mass}, mass_ratio: {}", big_mass / small_mass);
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    testbed.look_at(point![10.0, 10.0, 10.0], Point::origin());
+}