Move 2D benchmarks into their own directory/crate.

10 files changed, 682 insertions, 0 deletions

diff --git a/benchmarks2d/Cargo.toml b/benchmarks2d/Cargo.toml
new file mode 100644
index 0000000..b1ee8db
--- /dev/null
+++ b/benchmarks2d/Cargo.toml
@@ -0,0 +1,27 @@
+[package]
+name    = "rapier-benchmarks-2d"
+version = "0.1.0"
+authors = [ "Sébastien Crozet <developer@crozet.re>" ]
+edition = "2018"
+
+[features]
+parallel = [ "rapier2d/parallel", "rapier_testbed2d/parallel" ]
+simd-stable = [ "rapier2d/simd-stable" ]
+simd-nightly = [ "rapier2d/simd-nightly" ]
+other-backends = [ "rapier_testbed2d/other-backends" ]
+enhanced-determinism = [ "rapier2d/enhanced-determinism" ]
+
+[dependencies]
+rand       = "0.7"
+Inflector  = "0.11"
+nalgebra = "0.22"
+
+[dependencies.rapier_testbed2d]
+path = "../build/rapier_testbed2d"
+
+[dependencies.rapier2d]
+path = "../build/rapier2d"
+
+[[bin]]
+name = "all_benchmarks2"
+path = "./all_benchmarks2.rs"
\ No newline at end of file
diff --git a/benchmarks2d/all_benchmarks2.rs b/benchmarks2d/all_benchmarks2.rs
new file mode 100644
index 0000000..9a7a607
--- /dev/null
+++ b/benchmarks2d/all_benchmarks2.rs
@@ -0,0 +1,82 @@
+#![allow(dead_code)]
+
+extern crate nalgebra as na;
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen::prelude::*;
+
+use inflector::Inflector;
+
+use rapier_testbed2d::Testbed;
+use std::cmp::Ordering;
+
+mod balls2;
+mod boxes2;
+mod capsules2;
+mod heightfield2;
+mod joint_ball2;
+mod joint_fixed2;
+mod joint_prismatic2;
+mod pyramid2;
+
+fn demo_name_from_command_line() -> Option<String> {
+    let mut args = std::env::args();
+
+    while let Some(arg) = args.next() {
+        if &arg[..] == "--example" {
+            return args.next();
+        }
+    }
+
+    None
+}
+
+#[cfg(any(target_arch = "wasm32", target_arch = "asmjs"))]
+fn demo_name_from_url() -> Option<String> {
+    None
+    //    let window = stdweb::web::window();
+    //    let hash = window.location()?.search().ok()?;
+    //    Some(hash[1..].to_string())
+}
+
+#[cfg(not(any(target_arch = "wasm32", target_arch = "asmjs")))]
+fn demo_name_from_url() -> Option<String> {
+    None
+}
+
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen(start))]
+pub fn main() {
+    let demo = demo_name_from_command_line()
+        .or_else(|| demo_name_from_url())
+        .unwrap_or(String::new())
+        .to_camel_case();
+
+    let mut builders: Vec<(_, fn(&mut Testbed))> = vec![
+        ("Balls", balls2::init_world),
+        ("Boxes", boxes2::init_world),
+        ("Capsules", capsules2::init_world),
+        ("Heightfield", heightfield2::init_world),
+        ("Pyramid", pyramid2::init_world),
+        ("(Stress test) joint ball", joint_ball2::init_world),
+        ("(Stress test) joint fixed", joint_fixed2::init_world),
+        (
+            "(Stress test) joint prismatic",
+            joint_prismatic2::init_world,
+        ),
+    ];
+
+    // Lexicographic sort, with stress tests moved at the end of the list.
+    builders.sort_by(|a, b| match (a.0.starts_with("("), b.0.starts_with("(")) {
+        (true, true) | (false, false) => a.0.cmp(b.0),
+        (true, false) => Ordering::Greater,
+        (false, true) => Ordering::Less,
+    });
+
+    let i = builders
+        .iter()
+        .position(|builder| builder.0.to_camel_case().as_str() == demo.as_str())
+        .unwrap_or(0);
+    let testbed = Testbed::from_builders(i, builders);
+
+    testbed.run()
+}
diff --git a/benchmarks2d/balls2.rs b/benchmarks2d/balls2.rs
new file mode 100644
index 0000000..6791505
--- /dev/null
+++ b/benchmarks2d/balls2.rs
@@ -0,0 +1,68 @@
+use na::Point2;
+use rapier2d::dynamics::{BodyStatus, 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();
+    /*
+     * Ground
+     */
+    let _ground_size = 25.0;
+
+    /*
+    let ground_shape = ShapeHandle::new(Cuboid::new(Vector2::new(ground_size, 1.0)));
+
+    let ground_handle = bodies.insert(Ground::new());
+    let co = ColliderDesc::new(ground_shape)
+        .translation(-Vector2::y())
+        .build(BodyPartHandle(ground_handle, 0));
+    colliders.insert(co);
+    */
+
+    /*
+     * Create the balls
+     */
+    let num = 50;
+    let rad = 1.0;
+
+    let shiftx = rad * 2.5;
+    let shifty = rad * 2.0;
+    let centerx = shiftx * (num as f32) / 2.0;
+    let centery = shifty / 2.0;
+
+    for i in 0..num {
+        for j in 0usize..num * 5 {
+            let x = i as f32 * shiftx - centerx;
+            let y = j as f32 * shifty + centery;
+
+            let status = if j == 0 {
+                BodyStatus::Static
+            } else {
+                BodyStatus::Dynamic
+            };
+
+            // Build the rigid body.
+            let rigid_body = RigidBodyBuilder::new(status).translation(x, y).build();
+            let handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::ball(rad).build();
+            colliders.insert(collider, handle, &mut bodies);
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(0.0, 2.5), 5.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Balls", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/boxes2.rs b/benchmarks2d/boxes2.rs
new file mode 100644
index 0000000..4fb9bf3
--- /dev/null
+++ b/benchmarks2d/boxes2.rs
@@ -0,0 +1,73 @@
+use na::Point2;
+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();
+
+    /*
+     * Ground
+     */
+    let ground_size = 25.0;
+
+    let rigid_body = RigidBodyBuilder::new_static().build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size, 1.2).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    let rigid_body = RigidBodyBuilder::new_static()
+        .rotation(std::f32::consts::FRAC_PI_2)
+        .translation(ground_size, ground_size * 2.0)
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size * 2.0, 1.2).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    let rigid_body = RigidBodyBuilder::new_static()
+        .rotation(std::f32::consts::FRAC_PI_2)
+        .translation(-ground_size, ground_size * 2.0)
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size * 2.0, 1.2).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * Create the cubes
+     */
+    let num = 26;
+    let rad = 0.5;
+
+    let shift = rad * 2.0;
+    let centerx = shift * (num as f32) / 2.0;
+    let centery = shift / 2.0;
+
+    for i in 0..num {
+        for j in 0usize..num * 5 {
+            let x = i as f32 * shift - centerx;
+            let y = j as f32 * shift + centery + 2.0;
+
+            // Build the rigid body.
+            let rigid_body = RigidBodyBuilder::new_dynamic().translation(x, y).build();
+            let handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::cuboid(rad, rad).build();
+            colliders.insert(collider, handle, &mut bodies);
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(0.0, 50.0), 10.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Balls", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/capsules2.rs b/benchmarks2d/capsules2.rs
new file mode 100644
index 0000000..76633bc
--- /dev/null
+++ b/benchmarks2d/capsules2.rs
@@ -0,0 +1,74 @@
+use na::Point2;
+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();
+
+    /*
+     * Ground
+     */
+    let ground_size = 25.0;
+
+    let rigid_body = RigidBodyBuilder::new_static().build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size, 1.2).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    let rigid_body = RigidBodyBuilder::new_static()
+        .rotation(std::f32::consts::FRAC_PI_2)
+        .translation(ground_size, ground_size * 4.0)
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size * 4.0, 1.2).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    let rigid_body = RigidBodyBuilder::new_static()
+        .rotation(std::f32::consts::FRAC_PI_2)
+        .translation(-ground_size, ground_size * 4.0)
+        .build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size * 4.0, 1.2).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * Create the cubes
+     */
+    let num = 26;
+    let rad = 0.5;
+
+    let shift = rad * 2.0;
+    let shifty = rad * 5.0;
+    let centerx = shift * (num as f32) / 2.0;
+    let centery = shift / 2.0;
+
+    for i in 0..num {
+        for j in 0usize..num * 5 {
+            let x = i as f32 * shift - centerx;
+            let y = j as f32 * shifty + centery + 3.0;
+
+            // Build the rigid body.
+            let rigid_body = RigidBodyBuilder::new_dynamic().translation(x, y).build();
+            let handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::capsule_y(rad * 1.5, rad).build();
+            colliders.insert(collider, handle, &mut bodies);
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(0.0, 50.0), 10.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Balls", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/heightfield2.rs b/benchmarks2d/heightfield2.rs
new file mode 100644
index 0000000..95fed6c
--- /dev/null
+++ b/benchmarks2d/heightfield2.rs
@@ -0,0 +1,72 @@
+use na::{DVector, 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();
+
+    /*
+     * Ground
+     */
+    let ground_size = Vector2::new(50.0, 1.0);
+    let nsubdivs = 2000;
+
+    let heights = DVector::from_fn(nsubdivs + 1, |i, _| {
+        if i == 0 || i == nsubdivs {
+            80.0
+        } else {
+            (i as f32 * ground_size.x / (nsubdivs as f32)).cos() * 2.0
+        }
+    });
+
+    let rigid_body = RigidBodyBuilder::new_static().build();
+    let handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::heightfield(heights, ground_size).build();
+    colliders.insert(collider, handle, &mut bodies);
+
+    /*
+     * Create the cubes
+     */
+    let num = 26;
+    let rad = 0.5;
+
+    let shift = rad * 2.0;
+    let centerx = shift * (num / 2) as f32;
+    let centery = shift / 2.0;
+
+    for i in 0..num {
+        for j in 0usize..num * 5 {
+            let x = i as f32 * shift - centerx;
+            let y = j as f32 * shift + centery + 3.0;
+
+            // Build the rigid body.
+            let rigid_body = RigidBodyBuilder::new_dynamic().translation(x, y).build();
+            let handle = bodies.insert(rigid_body);
+
+            if j % 2 == 0 {
+                let collider = ColliderBuilder::cuboid(rad, rad).build();
+                colliders.insert(collider, handle, &mut bodies);
+            } else {
+                let collider = ColliderBuilder::ball(rad).build();
+                colliders.insert(collider, handle, &mut bodies);
+            }
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(0.0, 50.0), 10.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Heightfield", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/joint_ball2.rs b/benchmarks2d/joint_ball2.rs
new file mode 100644
index 0000000..ecfdc47
--- /dev/null
+++ b/benchmarks2d/joint_ball2.rs
@@ -0,0 +1,72 @@
+use na::Point2;
+use rapier2d::dynamics::{BallJoint, BodyStatus, 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 mut joints = JointSet::new();
+
+    /*
+     * Create the balls
+     */
+    // Build the rigid body.
+    let rad = 0.4;
+    let numi = 100; // Num vertical nodes.
+    let numk = 100; // Num horizontal nodes.
+    let shift = 1.0;
+
+    let mut body_handles = Vec::new();
+
+    for k in 0..numk {
+        for i in 0..numi {
+            let fk = k as f32;
+            let fi = i as f32;
+
+            let status = if k >= numk / 2 - 3 && k <= numk / 2 + 3 && i == 0 {
+                BodyStatus::Static
+            } else {
+                BodyStatus::Dynamic
+            };
+
+            let rigid_body = RigidBodyBuilder::new(status)
+                .translation(fk * shift, -fi * shift)
+                .build();
+            let child_handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::ball(rad).build();
+            colliders.insert(collider, child_handle, &mut bodies);
+
+            // Vertical joint.
+            if i > 0 {
+                let parent_handle = *body_handles.last().unwrap();
+                let joint = BallJoint::new(Point2::origin(), Point2::new(0.0, shift));
+                joints.insert(&mut bodies, parent_handle, child_handle, joint);
+            }
+
+            // Horizontal joint.
+            if k > 0 {
+                let parent_index = body_handles.len() - numi;
+                let parent_handle = body_handles[parent_index];
+                let joint = BallJoint::new(Point2::origin(), Point2::new(-shift, 0.0));
+                joints.insert(&mut bodies, parent_handle, child_handle, joint);
+            }
+
+            body_handles.push(child_handle);
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(numk as f32 * rad, numi as f32 * -rad), 5.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Joints", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/joint_fixed2.rs b/benchmarks2d/joint_fixed2.rs
new file mode 100644
index 0000000..32a219e
--- /dev/null
+++ b/benchmarks2d/joint_fixed2.rs
@@ -0,0 +1,85 @@
+use na::{Isometry2, Point2};
+use rapier2d::dynamics::{BodyStatus, FixedJoint, 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 mut joints = JointSet::new();
+
+    /*
+     * Create the balls
+     */
+    // Build the rigid body.
+    let rad = 0.4;
+    let num = 30; // Num vertical nodes.
+    let shift = 1.0;
+
+    let mut body_handles = Vec::new();
+
+    for xx in 0..4 {
+        let x = xx as f32 * shift * (num as f32 + 2.0);
+
+        for yy in 0..4 {
+            let y = yy as f32 * shift * (num as f32 + 4.0);
+
+            for k in 0..num {
+                for i in 0..num {
+                    let fk = k as f32;
+                    let fi = i as f32;
+
+                    let status = if k == 0 {
+                        BodyStatus::Static
+                    } else {
+                        BodyStatus::Dynamic
+                    };
+
+                    let rigid_body = RigidBodyBuilder::new(status)
+                        .translation(x + fk * shift, y - fi * shift)
+                        .build();
+                    let child_handle = bodies.insert(rigid_body);
+                    let collider = ColliderBuilder::ball(rad).build();
+                    colliders.insert(collider, child_handle, &mut bodies);
+
+                    // Vertical joint.
+                    if i > 0 {
+                        let parent_handle = *body_handles.last().unwrap();
+                        let joint = FixedJoint::new(
+                            Isometry2::identity(),
+                            Isometry2::translation(0.0, shift),
+                        );
+                        joints.insert(&mut bodies, parent_handle, child_handle, joint);
+                    }
+
+                    // Horizontal joint.
+                    if k > 0 {
+                        let parent_index = body_handles.len() - num;
+                        let parent_handle = body_handles[parent_index];
+                        let joint = FixedJoint::new(
+                            Isometry2::identity(),
+                            Isometry2::translation(-shift, 0.0),
+                        );
+                        joints.insert(&mut bodies, parent_handle, child_handle, joint);
+                    }
+
+                    body_handles.push(child_handle);
+                }
+            }
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(50.0, 50.0), 5.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Joints", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/joint_prismatic2.rs b/benchmarks2d/joint_prismatic2.rs
new file mode 100644
index 0000000..91ef48e
--- /dev/null
+++ b/benchmarks2d/joint_prismatic2.rs
@@ -0,0 +1,69 @@
+use na::{Point2, Unit, Vector2};
+use rapier2d::dynamics::{JointSet, PrismaticJoint, 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 mut joints = JointSet::new();
+
+    /*
+     * Create the balls
+     */
+    // Build the rigid body.
+    let rad = 0.4;
+    let num = 10;
+    let shift = 1.0;
+
+    for l in 0..25 {
+        let y = l as f32 * shift * (num as f32 + 2.0) * 2.0;
+
+        for j in 0..50 {
+            let x = j as f32 * shift * 4.0;
+
+            let ground = RigidBodyBuilder::new_static().translation(x, y).build();
+            let mut curr_parent = bodies.insert(ground);
+            let collider = ColliderBuilder::cuboid(rad, rad).build();
+            colliders.insert(collider, curr_parent, &mut bodies);
+
+            for i in 0..num {
+                let y = y - (i + 1) as f32 * shift;
+                let density = 1.0;
+                let rigid_body = RigidBodyBuilder::new_dynamic().translation(x, y).build();
+                let curr_child = bodies.insert(rigid_body);
+                let collider = ColliderBuilder::cuboid(rad, rad).density(density).build();
+                colliders.insert(collider, curr_child, &mut bodies);
+
+                let axis = if i % 2 == 0 {
+                    Unit::new_normalize(Vector2::new(1.0, 1.0))
+                } else {
+                    Unit::new_normalize(Vector2::new(-1.0, 1.0))
+                };
+
+                let mut prism =
+                    PrismaticJoint::new(Point2::origin(), axis, Point2::new(0.0, shift), axis);
+                prism.limits_enabled = true;
+                prism.limits[0] = -1.5;
+                prism.limits[1] = 1.5;
+                joints.insert(&mut bodies, curr_parent, curr_child, prism);
+
+                curr_parent = curr_child;
+            }
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(80.0, 80.0), 15.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Joints", init_world)]);
+    testbed.run()
+}
diff --git a/benchmarks2d/pyramid2.rs b/benchmarks2d/pyramid2.rs
new file mode 100644
index 0000000..e6a715b
--- /dev/null
+++ b/benchmarks2d/pyramid2.rs
@@ -0,0 +1,60 @@
+use na::Point2;
+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();
+
+    /*
+     * Ground
+     */
+    let ground_size = 100.0;
+    let ground_thickness = 1.0;
+
+    let rigid_body = RigidBodyBuilder::new_static().build();
+    let ground_handle = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(ground_size, ground_thickness).build();
+    colliders.insert(collider, ground_handle, &mut bodies);
+
+    /*
+     * Create the cubes
+     */
+    let num = 100;
+    let rad = 0.5;
+
+    let shift = rad * 2.0;
+    let centerx = shift * (num as f32) / 2.0;
+    let centery = shift / 2.0 + ground_thickness + rad * 1.5;
+
+    for i in 0usize..num {
+        for j in i..num {
+            let fj = j as f32;
+            let fi = i as f32;
+            let x = (fi * shift / 2.0) + (fj - fi) * shift - centerx;
+            let y = fi * shift + centery;
+
+            // Build the rigid body.
+            let rigid_body = RigidBodyBuilder::new_dynamic().translation(x, y).build();
+            let handle = bodies.insert(rigid_body);
+            let collider = ColliderBuilder::cuboid(rad, rad).build();
+            colliders.insert(collider, handle, &mut bodies);
+        }
+    }
+
+    /*
+     * Set up the testbed.
+     */
+    testbed.set_world(bodies, colliders, joints);
+    testbed.look_at(Point2::new(0.0, 2.5), 5.0);
+}
+
+fn main() {
+    let testbed = Testbed::from_builders(0, vec![("Balls", init_world)]);
+    testbed.run()
+}