Remove the Salva integration code from rapier + add a plugin system to the testbed.

14 files changed, 102 insertions, 619 deletions

diff --git a/Cargo.toml b/Cargo.toml
index a320df1..cfb166a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,8 +10,6 @@ members = [ "build/rapier2d", "build/rapier_testbed2d", "examples2d", "benchmark
 #nphysics2d = { path = "../nphysics/build/nphysics2d" }
 #nphysics3d = { path = "../nphysics/build/nphysics3d" }
 #kiss3d = { path = "../kiss3d" }
-salva2d = { path = "../salva/build/salva2d" }
-salva3d = { path = "../salva/build/salva3d" }
 
 [profile.release]
 #debug = true
diff --git a/build/rapier2d/Cargo.toml b/build/rapier2d/Cargo.toml
index 30818f4..1c24a5d 100644
--- a/build/rapier2d/Cargo.toml
+++ b/build/rapier2d/Cargo.toml
@@ -23,7 +23,6 @@ simd-is-enabled = [ ]
 wasm-bindgen = [ "instant/wasm-bindgen" ]
 serde-serialize = [ "erased-serde", "nalgebra/serde-serialize", "ncollide2d/serde-serialize", "serde", "generational-arena/serde", "bit-vec/serde", "arrayvec/serde" ]
 enhanced-determinism = [ "simba/libm_force", "indexmap" ]
-fluids = [ "salva2d" ]
 
 [lib]
 name = "rapier2d"
@@ -51,7 +50,6 @@ indexmap = { version = "1", features = [ "serde-1" ], optional = true }
 downcast-rs = "1.2"
 num-derive = "0.3"
 bitflags = "1"
-salva2d = { version = "0.4", optional = true }
 
 [dev-dependencies]
 bincode = "1"
diff --git a/build/rapier3d/Cargo.toml b/build/rapier3d/Cargo.toml
index 3d77440..7e98cdf 100644
--- a/build/rapier3d/Cargo.toml
+++ b/build/rapier3d/Cargo.toml
@@ -23,7 +23,6 @@ simd-is-enabled = [ ]
 wasm-bindgen = [ "instant/wasm-bindgen" ]
 serde-serialize = [ "erased-serde", "nalgebra/serde-serialize", "ncollide3d/serde-serialize", "serde", "generational-arena/serde", "bit-vec/serde" ]
 enhanced-determinism = [ "simba/libm_force", "indexmap" ]
-fluids = [ "salva3d" ]
 
 [lib]
 name = "rapier3d"
@@ -51,7 +50,6 @@ indexmap = { version = "1", features = [ "serde-1" ], optional = true }
 downcast-rs = "1.2"
 num-derive = "0.3"
 bitflags = "1"
-salva3d = { version = "0.4", optional = true }
 
 [dev-dependencies]
 bincode = "1"
diff --git a/build/rapier_testbed2d/Cargo.toml b/build/rapier_testbed2d/Cargo.toml
index 08c0893..273595f 100644
--- a/build/rapier_testbed2d/Cargo.toml
+++ b/build/rapier_testbed2d/Cargo.toml
@@ -39,7 +39,6 @@ flexbuffers = "0.1"
 Inflector  = "0.11"
 md5 = "0.7"
 
-
 [dependencies.rapier2d]
 path = "../rapier2d"
 version = "0.3"
diff --git a/examples2d/Cargo.toml b/examples2d/Cargo.toml
index 603f9c7..f1ed728 100644
--- a/examples2d/Cargo.toml
+++ b/examples2d/Cargo.toml
@@ -10,7 +10,6 @@ simd-stable = [ "rapier2d/simd-stable" ]
 simd-nightly = [ "rapier2d/simd-nightly" ]
 other-backends = [ "rapier_testbed2d/other-backends" ]
 enhanced-determinism = [ "rapier2d/enhanced-determinism" ]
-fluids = [ "rapier2d/fluids" ]
 
 [dependencies]
 rand       = "0.7"
diff --git a/examples3d/Cargo.toml b/examples3d/Cargo.toml
index 23118aa..5362554 100644
--- a/examples3d/Cargo.toml
+++ b/examples3d/Cargo.toml
@@ -10,7 +10,6 @@ simd-stable = [ "rapier3d/simd-stable" ]
 simd-nightly = [ "rapier3d/simd-nightly" ]
 other-backends = [ "rapier_testbed3d/other-backends" ]
 enhanced-determinism = [ "rapier3d/enhanced-determinism" ]
-fluids = [ "rapier3d/fluids" ]
 
 [dependencies]
 rand       = "0.7"
diff --git a/src/geometry/shape.rs b/src/geometry/shape.rs
index ec43bf7..5c96f68 100644
--- a/src/geometry/shape.rs
+++ b/src/geometry/shape.rs
@@ -64,6 +64,8 @@ pub trait Shape: RayCast<f32> + PointQuery<f32> + DowncastSync {
         None
     }
 
+    // TODO: add a compute_local_aabb method?
+
     /// Computes the AABB of this shape.
     fn compute_aabb(&self, position: &Isometry<f32>) -> AABB<f32>;
 
diff --git a/src/lib.rs b/src/lib.rs
index 9d2860a..deb9313 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -16,10 +16,6 @@ pub extern crate nalgebra as na;
 pub extern crate ncollide2d as ncollide;
 #[cfg(feature = "dim3")]
 pub extern crate ncollide3d as ncollide;
-#[cfg(feature = "dim2")]
-pub extern crate salva2d as salva;
-#[cfg(feature = "dim3")]
-pub extern crate salva3d as salva;
 #[cfg(feature = "serde")]
 #[macro_use]
 extern crate serde;
diff --git a/src/pipeline/fluids_pipeline.rs b/src/pipeline/fluids_pipeline.rs
deleted file mode 100644
index 8d1a8d5..0000000
--- a/src/pipeline/fluids_pipeline.rs
+++ /dev/null
@@ -1,293 +0,0 @@
-use crate::approx::AbsDiffEq;
-use crate::dynamics::RigidBodySet;
-use crate::geometry::{ColliderHandle, ColliderSet};
-use crate::math::{Point, Vector};
-use crate::salva::solver::DFSPHSolver;
-use crate::salva::LiquidWorld;
-use na::{RealField, Unit};
-use ncollide::bounding_volume::BoundingVolume;
-use ncollide::query::PointQuery;
-use ncollide::shape::FeatureId;
-use salva::coupling::CouplingManager;
-use salva::geometry::{HGrid, HGridEntry};
-use salva::object::{BoundaryHandle, BoundarySet, Fluid};
-use salva::TimestepManager;
-use std::collections::HashMap;
-use std::sync::RwLock;
-
-/// Pipeline for particle-based fluid simulation.
-pub struct FluidsPipeline {
-    liquid_world: LiquidWorld,
-    coupling: ColliderCouplingSet,
-}
-
-impl FluidsPipeline {
-    /// Initialize a new pipeline for fluids simulation.
-    ///
-    /// # Parameters
-    ///
-    /// - `particle_radius`: the radius of every particle for the fluid simulation.
-    /// - `smoothing_factor`: the smoothing factor used to compute the SPH kernel radius.
-    ///    The kernel radius will be computed as `particle_radius * smoothing_factor * 2.0.
-    pub fn new(particle_radius: f32, smoothing_factor: f32) -> Self {
-        let dfsph: DFSPHSolver = DFSPHSolver::new();
-
-        Self {
-            liquid_world: LiquidWorld::new(dfsph, particle_radius, smoothing_factor),
-            coupling: ColliderCouplingSet::new(),
-        }
-    }
-
-    /// Advances the fluid simulation by `dt` milliseconds.
-    ///
-    /// All the fluid particles will be affected by an acceleration equal to `gravity`.
-    /// This `step` function may apply forces to some rigid-bodies that interact with fluids.
-    /// However, it will not integrate these forces. Use the `PhysicsPipeline` for this integration.
-    pub fn step(
-        &mut self,
-        gravity: &Vector<f32>,
-        dt: f32,
-        colliders: &ColliderSet,
-        bodies: &mut RigidBodySet,
-    ) {
-        self.liquid_world.step_with_coupling(
-            dt,
-            gravity,
-            &mut self.coupling.as_manager_mut(colliders, bodies),
-        )
-    }
-}
-
-/// The way a collider is coupled to a boundary object.
-pub enum ParticleSampling {
-    /// The collider shape is approximated with the given sample points in local-space.
-    ///
-    /// It is recommended that those points are separated by a distance smaller or equal to twice
-    /// the particle radius used to initialize the LiquidWorld.
-    StaticSampling(Vec<Point<f32>>),
-    /// The collider shape is approximated by a dynamic set of points automatically computed based on contacts with fluid particles.
-    DynamicContactSampling,
-}
-
-struct ColliderCouplingEntry {
-    coupling_method: ParticleSampling,
-    boundary: BoundaryHandle,
-    features: Vec<FeatureId>,
-}
-
-/// Structure managing all the coupling between colliders from rapier with boundaries and fluids from salva.
-pub struct ColliderCouplingSet {
-    entries: HashMap<ColliderHandle, ColliderCouplingEntry>,
-}
-
-impl ColliderCouplingSet {
-    /// Create a new collider coupling manager.
-    pub fn new() -> Self {
-        Self {
-            entries: HashMap::new(),
-        }
-    }
-
-    /// Register a coupling between a boundary and a collider.
-    /// There can be only up to one coupling between a collider and a boundary object. If a coupling
-    /// already exists for this collider when calling this function, the handle of the previously coupled
-    /// boundary is returned.
-    pub fn register_coupling(
-        &mut self,
-        boundary: BoundaryHandle,
-        collider: ColliderHandle,
-        coupling_method: ParticleSampling,
-    ) -> Option<BoundaryHandle> {
-        let old = self.entries.insert(
-            collider,
-            ColliderCouplingEntry {
-                coupling_method,
-                boundary,
-                features: Vec::new(),
-            },
-        );
-
-        old.map(|e| e.boundary)
-    }
-
-    /// Unregister a coupling between a boundary and a collider.
-    /// Note that this does not remove the boundary itself from the liquid world.
-    /// Returns the handle of the boundary this collider was coupled with.
-    pub fn unregister_coupling(&mut self, collider: ColliderHandle) -> Option<BoundaryHandle> {
-        let deleted = self.entries.remove(&collider);
-        deleted.map(|e| e.boundary)
-    }
-
-    /// Use this collider coupling set as a coupling manager.
-    pub fn as_manager_mut<'a>(
-        &'a mut self,
-        colliders: &'a ColliderSet,
-        bodies: &'a mut RigidBodySet,
-    ) -> ColliderCouplingManager {
-        ColliderCouplingManager {
-            coupling: self,
-            colliders,
-            bodies,
-        }
-    }
-}
-
-/// A manager for coupling colliders from rapier2d/rapier3D with the boundary
-/// objects from salva.
-pub struct ColliderCouplingManager<'a> {
-    coupling: &'a mut ColliderCouplingSet,
-    colliders: &'a ColliderSet,
-    bodies: &'a mut RigidBodySet,
-}
-
-impl<'a> CouplingManager for ColliderCouplingManager<'a> {
-    fn update_boundaries(
-        &mut self,
-        timestep: &TimestepManager,
-        h: f32,
-        particle_radius: f32,
-        hgrid: &HGrid<HGridEntry>,
-        fluids: &mut [Fluid],
-        boundaries: &mut BoundarySet,
-    ) {
-        for (collider, coupling) in &mut self.coupling.entries {
-            if let (Some(collider), Some(boundary)) = (
-                self.colliders.get(*collider),
-                boundaries.get_mut(coupling.boundary),
-            ) {
-                // Update the boundary's ability to receive forces.
-                let body = self.bodies.get(collider.parent());
-                if let Some(body) = body {
-                    if !body.is_dynamic() {
-                        boundary.forces = None;
-                    } else {
-                        boundary.forces = Some(RwLock::new(Vec::new()));
-                        boundary.clear_forces(true);
-                    }
-                }
-
-                // Update positions and velocities.
-                boundary.positions.clear();
-                boundary.velocities.clear();
-                boundary.volumes.clear();
-                coupling.features.clear();
-
-                match &coupling.coupling_method {
-                    ParticleSampling::StaticSampling(points) => {
-                        for pt in points {
-                            boundary.positions.push(collider.position() * pt);
-                            // FIXME: how do we get the point-velocity of deformable bodies correctly?
-                            let velocity = body.map(|b| b.velocity_at_point(pt));
-
-                            boundary
-                                .velocities
-                                .push(velocity.unwrap_or(Vector::zeros()));
-                        }
-
-                        boundary.volumes.resize(points.len(), na::zero::<f32>());
-                    }
-                    ParticleSampling::DynamicContactSampling => {
-                        let prediction = h * na::convert::<_, f32>(0.5);
-                        let margin = particle_radius * na::convert::<_, f32>(0.1);
-                        let collider_pos = collider.position();
-                        let aabb = collider
-                            .shape()
-                            .compute_aabb(&collider_pos)
-                            .loosened(h + prediction);
-
-                        for particle in hgrid
-                            .cells_intersecting_aabb(&aabb.mins, &aabb.maxs)
-                            .flat_map(|e| e.1)
-                        {
-                            match particle {
-                                HGridEntry::FluidParticle(fluid_id, particle_id) => {
-                                    let fluid = &mut fluids[*fluid_id];
-                                    let particle_pos = fluid.positions[*particle_id]
-                                        + fluid.velocities[*particle_id] * timestep.dt();
-
-                                    if aabb.contains_local_point(&particle_pos) {
-                                        let (proj, feature) =
-                                            collider.shape().project_point_with_feature(
-                                                &collider_pos,
-                                                &particle_pos,
-                                            );
-
-                                        let dpt = particle_pos - proj.point;
-
-                                        if let Some((normal, depth)) =
-                                            Unit::try_new_and_get(dpt, f32::default_epsilon())
-                                        {
-                                            if proj.is_inside {
-                                                fluid.positions[*particle_id] -=
-                                                    *normal * (depth + margin);
-
-                                                let vel_err =
-                                                    normal.dot(&fluid.velocities[*particle_id]);
-
-                                                if vel_err > na::zero::<f32>() {
-                                                    fluid.velocities[*particle_id] -=
-                                                        *normal * vel_err;
-                                                }
-                                            } else if depth > h + prediction {
-                                                continue;
-                                            }
-                                        }
-
-                                        let velocity =
-                                            body.map(|b| b.velocity_at_point(&proj.point));
-
-                                        boundary
-                                            .velocities
-                                            .push(velocity.unwrap_or(Vector::zeros()));
-                                        boundary.positions.push(proj.point);
-                                        boundary.volumes.push(na::zero::<f32>());
-                                        coupling.features.push(feature);
-                                    }
-                                }
-                                HGridEntry::BoundaryParticle(..) => {
-                                    // Not yet implemented.
-                                }
-                            }
-                        }
-                    }
-                }
-
-                boundary.clear_forces(true);
-            }
-        }
-    }
-
-    fn transmit_forces(&mut self, boundaries: &BoundarySet) {
-        for (collider, coupling) in &self.coupling.entries {
-            if let (Some(collider), Some(boundary)) = (
-                self.colliders.get(*collider),
-                boundaries.get(coupling.boundary),
-            ) {
-                if boundary.positions.is_empty() {
-                    continue;
-                }
-
-                if let Some(forces) = &boundary.forces {
-                    let forces = forces.read().unwrap();
-                    if let Some(mut body) = self.bodies.get_mut(collider.parent) {
-                        for (pos, force) in boundary.positions.iter().zip(forces.iter().cloned()) {
-                            // FIXME: how do we deal with large density ratio?
-                            // Is it only an issue with PBF?
-                            // The following commented code was an attempt to limit the force applied
-                            // to the bodies in order to avoid large forces.
-                            //
-                            //                                let ratio = na::convert::<_, f32>(3.0)
-                            //                                    * body.part(body_part.1).unwrap().inertia().mass();
-                            //
-                            //                                if ratio < na::convert::<_, f32>(1.0) {
-                            //                                    force *= ratio;
-                            //                                }
-
-                            body.apply_force_at_point(force, *pos)
-                        }
-                    }
-                }
-            }
-        }
-    }
-}
diff --git a/src/pipeline/mod.rs b/src/pipeline/mod.rs
index 6212acb..287de9d 100644
--- a/src/pipeline/mod.rs
+++ b/src/pipeline/mod.rs
@@ -2,14 +2,10 @@
 
 pub use collision_pipeline::CollisionPipeline;
 pub use event_handler::{ChannelEventCollector, EventHandler};
-#[cfg(feature = "fluids")]
-pub use fluids_pipeline::FluidsPipeline;
 pub use physics_pipeline::PhysicsPipeline;
 pub use query_pipeline::QueryPipeline;
 
 mod collision_pipeline;
 mod event_handler;
-#[cfg(feature = "fluids")]
-mod fluids_pipeline;
 mod physics_pipeline;
 mod query_pipeline;
diff --git a/src_testbed/engine.rs b/src_testbed/engine.rs
index 52b9ca9..ff5e1ef 100644
--- a/src_testbed/engine.rs
+++ b/src_testbed/engine.rs
@@ -15,15 +15,11 @@ use rapier::dynamics::{RigidBodyHandle, RigidBodySet};
 use rapier::geometry::{Collider, ColliderHandle, ColliderSet};
 //use crate::objects::capsule::Capsule;
 //use crate::objects::convex::Convex;
-//#[cfg(feature = "fluids")]
-//use crate::objects::fluid::Fluid as FluidNode;
 //#[cfg(feature = "dim3")]
 //use crate::objects::mesh::Mesh;
 //use crate::objects::plane::Plane;
 //#[cfg(feature = "dim2")]
 //use crate::objects::polyline::Polyline;
-//#[cfg(feature = "fluids")]
-//use crate::objects::FluidRenderingMode;
 use crate::objects::capsule::Capsule;
 #[cfg(feature = "dim3")]
 use crate::objects::cone::Cone;
@@ -58,22 +54,12 @@ impl GraphicsWindow for Window {
 pub struct GraphicsManager {
     rand: Pcg32,
     b2sn: HashMap<RigidBodyHandle, Vec<Node>>,
-    #[cfg(feature = "fluids")]
-    f2sn: HashMap<FluidHandle, FluidNode>,
-    #[cfg(feature = "fluids")]
-    boundary2sn: HashMap<BoundaryHandle, FluidNode>,
     b2color: HashMap<RigidBodyHandle, Point3<f32>>,
     c2color: HashMap<ColliderHandle, Point3<f32>>,
     b2wireframe: HashMap<RigidBodyHandle, bool>,
-    #[cfg(feature = "fluids")]
-    f2color: HashMap<FluidHandle, Point3<f32>>,
     ground_color: Point3<f32>,
     camera: Camera,
     ground_handle: Option<RigidBodyHandle>,
-    #[cfg(feature = "fluids")]
-    fluid_rendering_mode: FluidRenderingMode,
-    #[cfg(feature = "fluids")]
-    render_boundary_particles: bool,
 }
 
 impl GraphicsManager {
@@ -96,21 +82,11 @@ impl GraphicsManager {
             camera,
             rand: Pcg32::seed_from_u64(0),
             b2sn: HashMap::new(),
-            #[cfg(feature = "fluids")]
-            f2sn: HashMap::new(),
-            #[cfg(feature = "fluids")]
-            boundary2sn: HashMap::new(),
             b2color: HashMap::new(),
             c2color: HashMap::new(),
-            #[cfg(feature = "fluids")]
-            f2color: HashMap::new(),
             ground_color: Point3::new(0.5, 0.5, 0.5),
             b2wireframe: HashMap::new(),
             ground_handle: None,
-            #[cfg(feature = "fluids")]
-            fluid_rendering_mode: FluidRenderingMode::StaticColor,
-            #[cfg(feature = "fluids")]
-            render_boundary_particles: false,
         }
     }
 
@@ -118,20 +94,6 @@ impl GraphicsManager {
         self.ground_handle = handle
     }
 
-    #[cfg(feature = "fluids")]
-    pub fn set_fluid_rendering_mode(&mut self, mode: FluidRenderingMode) {
-        self.fluid_rendering_mode = mode;
-    }
-
-    #[cfg(feature = "fluids")]
-    pub fn enable_boundary_particles_rendering(&mut self, enabled: bool) {
-        self.render_boundary_particles = enabled;
-
-        for sn in self.boundary2sn.values_mut() {
-            sn.scene_node_mut().set_visible(enabled);
-        }
-    }
-
     pub fn clear(&mut self, window: &mut Window) {
         for sns in self.b2sn.values_mut() {
             for sn in sns.iter_mut() {
@@ -141,17 +103,7 @@ impl GraphicsManager {
             }
         }
 
-        #[cfg(feature = "fluids")]
-        for sn in self.f2sn.values_mut().chain(self.boundary2sn.values_mut()) {
-            let node = sn.scene_node_mut();
-            window.remove_graphics_node(node);
-        }
-
         self.b2sn.clear();
-        #[cfg(feature = "fluids")]
-        self.f2sn.clear();
-        #[cfg(feature = "fluids")]
-        self.boundary2sn.clear();
         self.c2color.clear();
         self.b2color.clear();
         self.b2wireframe.clear();
@@ -170,15 +122,6 @@ impl GraphicsManager {
         self.b2sn.remove(&body);
     }
 
-    #[cfg(feature = "fluids")]
-    pub fn set_fluid_color(&mut self, f: FluidHandle, color: Point3<f32>) {
-        self.f2color.insert(f, color);
-
-        if let Some(n) = self.f2sn.get_mut(&f) {
-            n.set_color(color)
-        }
-    }
-
     pub fn set_body_color(&mut self, b: RigidBodyHandle, color: Point3<f32>) {
         self.b2color.insert(b, color);
 
@@ -234,6 +177,10 @@ impl GraphicsManager {
         }
     }
 
+    pub fn next_color(&mut self) -> Point3<f32> {
+        Self::gen_color(&mut self.rand)
+    }
+
     fn gen_color(rng: &mut Pcg32) -> Point3<f32> {
         let mut color: Point3<f32> = rng.gen();
         color *= 1.5;
@@ -258,49 +205,6 @@ impl GraphicsManager {
         color
     }
 
-    #[cfg(feature = "fluids")]
-    pub fn add_fluid(
-        &mut self,
-        window: &mut Window,
-        handle: FluidHandle,
-        fluid: &Fluid<f32>,
-        particle_radius: f32,
-    ) {
-        let rand = &mut self.rand;
-        let color = *self
-            .f2color
-            .entry(handle)
-            .or_insert_with(|| Self::gen_color(rand));
-
-        self.add_fluid_with_color(window, handle, fluid, particle_radius, color);
-    }
-
-    #[cfg(feature = "fluids")]
-    pub fn add_boundary(
-        &mut self,
-        window: &mut Window,
-        handle: BoundaryHandle,
-        boundary: &Boundary<f32>,
-        particle_radius: f32,
-    ) {
-        let color = self.ground_color;
-        let node = FluidNode::new(particle_radius, &boundary.positions, color, window);
-        self.boundary2sn.insert(handle, node);
-    }
-
-    #[cfg(feature = "fluids")]
-    pub fn add_fluid_with_color(
-        &mut self,
-        window: &mut Window,
-        handle: FluidHandle,
-        fluid: &Fluid<f32>,
-        particle_radius: f32,
-        color: Point3<f32>,
-    ) {
-        let node = FluidNode::new(particle_radius, &fluid.positions, color, window);
-        self.f2sn.insert(handle, node);
-    }
-
     pub fn add(
         &mut self,
         window: &mut Window,
@@ -642,23 +546,6 @@ impl GraphicsManager {
     }
     */
 
-    #[cfg(feature = "fluids")]
-    pub fn draw_fluids(&mut self, liquid_world: &LiquidWorld<f32>) {
-        for (i, fluid) in liquid_world.fluids().iter() {
-            if let Some(node) = self.f2sn.get_mut(&i) {
-                node.update_with_fluid(fluid, self.fluid_rendering_mode)
-            }
-        }
-
-        if self.render_boundary_particles {
-            for (i, boundary) in liquid_world.boundaries().iter() {
-                if let Some(node) = self.boundary2sn.get_mut(&i) {
-                    node.update_with_boundary(boundary)
-                }
-            }
-        }
-    }
-
     pub fn draw(&mut self, _bodies: &RigidBodySet, colliders: &ColliderSet, window: &mut Window) {
         // use kiss3d::camera::Camera;
         // println!(
diff --git a/src_testbed/lib.rs b/src_testbed/lib.rs
index e077bb1..4b0830f 100644
--- a/src_testbed/lib.rs
+++ b/src_testbed/lib.rs
@@ -13,6 +13,10 @@ extern crate nphysics3d as nphysics;
 extern crate rapier2d as rapier;
 #[cfg(feature = "dim3")]
 extern crate rapier3d as rapier;
+#[cfg(all(feature = "dim2", feature = "fluids"))]
+extern crate salva2d as salva;
+#[cfg(all(feature = "dim3", feature = "fluids"))]
+extern crate salva3d as salva;
 
 #[macro_use]
 extern crate bitflags;
@@ -22,7 +26,8 @@ extern crate bitflags;
 extern crate log;
 
 pub use crate::engine::GraphicsManager;
-pub use crate::testbed::Testbed;
+pub use crate::plugin::TestbedPlugin;
+pub use crate::testbed::{PhysicsState, Testbed};
 
 #[cfg(all(feature = "dim2", feature = "other-backends"))]
 mod box2d_backend;
@@ -32,6 +37,7 @@ mod nphysics_backend;
 pub mod objects;
 #[cfg(all(feature = "dim3", feature = "other-backends"))]
 mod physx_backend;
+mod plugin;
 mod testbed;
 mod ui;
 
diff --git a/src_testbed/plugin.rs b/src_testbed/plugin.rs
new file mode 100644
index 0000000..7ad018b
--- /dev/null
+++ b/src_testbed/plugin.rs
@@ -0,0 +1,12 @@
+use crate::testbed::PhysicsState;
+use kiss3d::window::Window;
+use na::Point3;
+
+pub trait TestbedPlugin {
+    fn init_graphics(&mut self, window: &mut Window, gen_color: &mut dyn FnMut() -> Point3<f32>);
+    fn clear_graphics(&mut self, window: &mut Window);
+    fn run_callbacks(&mut self, window: &mut Window, physics: &mut PhysicsState, t: f32);
+    fn step(&mut self, physics: &mut PhysicsState);
+    fn draw(&mut self);
+    fn profiling_string(&self) -> String;
+}
diff --git a/src_testbed/testbed.rs b/src_testbed/testbed.rs
index 66b5953..7a72293 100644
--- a/src_testbed/testbed.rs
+++ b/src_testbed/testbed.rs
@@ -4,8 +4,7 @@ use std::path::Path;
 use std::rc::Rc;
 
 use crate::engine::GraphicsManager;
-#[cfg(feature = "fluids")]
-use crate::objects::FluidRenderingMode;
+use crate::plugin::TestbedPlugin;
 use crate::ui::TestbedUi;
 use crossbeam::channel::Receiver;
 use kiss3d::camera::Camera;
@@ -29,8 +28,6 @@ use rapier::geometry::{
 };
 use rapier::math::Vector;
 use rapier::pipeline::{ChannelEventCollector, PhysicsPipeline, QueryPipeline};
-#[cfg(feature = "fluids")]
-use salva::{coupling::ColliderCouplingSet, object::FluidHandle, LiquidWorld};
 
 #[cfg(all(feature = "dim2", feature = "other-backends"))]
 use crate::box2d_backend::Box2dWorld;
@@ -185,6 +182,8 @@ pub struct PhysicsState {
     pub joints: JointSet,
     pub pipeline: PhysicsPipeline,
     pub query_pipeline: QueryPipeline,
+    pub integration_parameters: IntegrationParameters,
+    pub gravity: Vector<f32>,
 }
 
 impl PhysicsState {
@@ -197,6 +196,8 @@ impl PhysicsState {
             joints: JointSet::new(),
             pipeline: PhysicsPipeline::new(),
             query_pipeline: QueryPipeline::new(),
+            integration_parameters: IntegrationParameters::default(),
+            gravity: Vector::y() * -9.81,
         }
     }
 }
@@ -225,25 +226,14 @@ pub struct TestbedState {
     pub timestep_id: usize,
 }
 
-#[cfg(feature = "fluids")]
-struct FluidsState {
-    world: LiquidWorld<f32>,
-    coupling: ColliderCouplingSet<f32, RigidBodyHandle>,
-}
-
 pub struct Testbed {
     builders: Vec<(&'static str, fn(&mut Testbed))>,
-    #[cfg(feature = "fluids")]
-    fluids: Option<FluidsState>,
-    gravity: Vector<f32>,
-    integration_parameters: IntegrationParameters,
     physics: PhysicsState,
     graphics: GraphicsManager,
     nsteps: usize,
     camera_locked: bool, // Used so that the camera can remain the same before and after we change backend or press the restart button.
     callbacks: Callbacks,
-    #[cfg(feature = "fluids")]
-    callbacks_fluids: CallbacksFluids,
+    plugins: Vec<Box<dyn TestbedPlugin>>,
     time: f32,
     hide_counters: bool,
     //    persistant_contacts: HashMap<ContactId, bool>,
@@ -264,20 +254,6 @@ pub struct Testbed {
 type Callbacks =
     Vec<Box<dyn FnMut(&mut Window, &mut PhysicsState, &PhysicsEvents, &mut GraphicsManager, f32)>>;
 
-#[cfg(feature = "fluids")]
-type CallbacksFluids = Vec<
-    Box<
-        dyn FnMut(
-            &mut Window,
-            &mut LiquidWorld<f32>,
-            &mut ColliderCouplingSet<f32, RigidBodyHandle>,
-            &mut PhysicsState,
-            &mut GraphicsManager,
-            f32,
-        ),
-    >,
->;
-
 impl Testbed {
     pub fn new_empty() -> Testbed {
         let graphics = GraphicsManager::new();
@@ -330,8 +306,6 @@ impl Testbed {
             thread_pool,
         };
 
-        let gravity = Vector::y() * -9.81;
-        let integration_parameters = IntegrationParameters::default();
         let contact_channel = crossbeam::channel::unbounded();
         let proximity_channel = crossbeam::channel::unbounded();
         let event_handler = ChannelEventCollector::new(proximity_channel.0, contact_channel.0);
@@ -343,14 +317,9 @@ impl Testbed {
 
         Testbed {
             builders: Vec::new(),
-            #[cfg(feature = "fluids")]
-            fluids: None,
-            gravity,
-            integration_parameters,
             physics,
             callbacks: Vec::new(),
-            #[cfg(feature = "fluids")]
-            callbacks_fluids: Vec::new(),
+            plugins: Vec::new(),
             graphics,
             nsteps: 1,
             camera_locked: false,
@@ -404,6 +373,14 @@ impl Testbed {
         self.hide_counters = false;
     }
 
+    pub fn integration_parameters_mut(&mut self) -> &mut IntegrationParameters {
+        &mut self.physics.integration_parameters
+    }
+
+    pub fn physics_state_mut(&mut self) -> &mut PhysicsState {
+        &mut self.physics
+    }
+
     pub fn set_world(&mut self, bodies: RigidBodySet, colliders: ColliderSet, joints: JointSet) {
         self.set_world_with_gravity(bodies, colliders, joints, Vector::y() * -9.81)
     }
@@ -451,8 +428,8 @@ impl Testbed {
                 || self.state.selected_backend == PHYSX_BACKEND_TWO_FRICTION_DIR
             {
                 self.physx = Some(PhysxWorld::from_rapier(
-                    self.gravity,
-                    &self.integration_parameters,
+                    self.physics.gravity,
+                    &self.physics.integration_parameters,
                     &self.physics.bodies,
                     &self.physics.colliders,
                     &self.physics.joints,
@@ -466,7 +443,7 @@ impl Testbed {
         {
             if self.state.selected_backend == NPHYSICS_BACKEND {
                 self.nphysics = Some(NPhysicsWorld::from_rapier(
-                    self.gravity,
+                    self.physics.gravity,
                     &self.physics.bodies,
                     &self.physics.colliders,
                     &self.physics.joints,
@@ -475,19 +452,6 @@ impl Testbed {
         }
     }
 
-    #[cfg(feature = "fluids")]
-    pub fn set_liquid_world(
-        &mut self,
-        mut liquid_world: LiquidWorld<f32>,
-        coupling: ColliderCouplingSet<f32, RigidBodyHandle>,
-    ) {
-        liquid_world.counters.enable();
-        self.fluids = Some(FluidsState {
-            world: liquid_world,
-            coupling,
-        });
-    }
-
     pub fn set_builders(&mut self, builders: Vec<(&'static str, fn(&mut Self))>) {
         self.state.example_names = builders.iter().map(|e| e.0).collect();
         self.builders = builders
@@ -515,25 +479,10 @@ impl Testbed {
         self.graphics.set_collider_initial_color(collider, color);
     }
 
-    #[cfg(feature = "fluids")]
-    pub fn set_flu