wip

20 files changed, 393 insertions, 89 deletions

diff --git a/src/config.rs b/src/config.rs
index 6a9d392..8739c53 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -6,6 +6,6 @@ pub const CELLS_IN_CHUNK: usize = (CHUNK_SIZE * CHUNK_SIZE) as usize;
 pub const CAMERA_MOVEMENT_SPEED: f32 = 40.0;
 
 pub const SIM_FPS: u32 = 120;
-pub const SIM_DELTA_TIME: f32 = 1.0 / SIM_FPS as f32;
+// pub const SIM_DELTA_TIME: f32 = 1.0 / SIM_FPS as f32;
 pub const PHYSICS_FPS: u32 = 60;
 pub const PHYSICS_DELTA_TIME: f32 = 1.0 / PHYSICS_FPS as f32;
diff --git a/src/main.rs b/src/main.rs
index bb4cb27..a01dbbd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -19,9 +19,13 @@ use winit::{
 
 use crate::{
     camera::Camera,
-    config::{PHYSICS_DELTA_TIME, PHYSICS_FPS, SIM_DELTA_TIME, SIM_FPS, WINDOW_TITLE},
+    config::{PHYSICS_DELTA_TIME, PHYSICS_FPS, SIM_FPS, WINDOW_TITLE},
     renderer::RendererState,
-    sim::{cell::Cell, materials::MaterialId, sim::sim_tick, world::World},
+    sim::{
+        cell::{cell::Cell, materials::MaterialId},
+        cell_sim::{sim::sim_tick, world::World},
+        rb_sim::{PhysicsManager, RbSimManager},
+    },
 };
 
 pub type Error = Box<dyn std::error::Error>;
@@ -58,8 +62,12 @@ struct App {
 
     camera: Option<Camera>,
 
+    // grid
     world: Option<World>,
 
+    // physics
+    rb_sim_manager: Option<RbSimManager>,
+
     // sim state
     // the last/current (not yet completed) seqno
     sim_seqno: u64,
@@ -122,8 +130,7 @@ impl App {
     // called SIM_FPS times per second
     // will be called before the render and before the physics update(s)
     // may be called multiple times if the sim time is behind
-    // sim_delta_time is statically 1/SIM_FPS
-    fn sim_update(&mut self, _sim_delta_time: f32) {
+    fn sim_update(&mut self) {
         if let Some(world) = &mut self.world {
             sim_tick(world, self.sim_seqno, self.config.use_threading);
             self.sim_seqno += 1;
@@ -133,7 +140,11 @@ impl App {
     // will be called before the render
     // may be called multiple times if the physics time is behind
     // physics_delta_time is statically 1/PHYSICS_FPS
-    fn physics_update(&mut self, _physics_delta_time: f32) {}
+    fn physics_update(&mut self, physics_delta_time: f32) {
+        if let Some(physics_manager) = &mut self.rb_sim_manager {
+            physics_manager.rb_tick(physics_delta_time);
+        }
+    }
 }
 
 impl Default for App {
@@ -157,6 +168,8 @@ impl Default for App {
 
             world: Some(World::from_default_size()),
 
+            rb_sim_manager: Some(RbSimManager::new()),
+
             sim_seqno: 0,
             sim_paused: false,
             ignore_pause_next_tick: false,
@@ -191,6 +204,9 @@ impl ApplicationHandler for App {
 
         self.window = Some(window.clone());
         self.renderer_state = Some(executor::block_on(RendererState::new(window.clone())));
+        if let Some(rbsm) = &mut self.rb_sim_manager {
+            rbsm.test();
+        }
 
         let size = window.inner_size();
         self.camera = Some(Camera::new((size.width as i32, size.height as i32)));
@@ -300,7 +316,7 @@ impl ApplicationHandler for App {
 
                 self.last_sim_update = now;
                 if self.sim_paused && self.ignore_pause_next_tick {
-                    self.sim_update(SIM_DELTA_TIME);
+                    self.sim_update();
                     self.ignore_pause_next_tick = false;
                 } else if !self.sim_paused {
                     self.sim_updates_due +=
@@ -308,7 +324,7 @@ impl ApplicationHandler for App {
                     let mut updates_done = 0;
                     // don't ever update more than 3 times per frame, or else we can get a pseudo deadlock
                     while self.sim_updates_due >= 1.0 && updates_done < 3 {
-                        self.sim_update(SIM_DELTA_TIME);
+                        self.sim_update();
                         updates_done += 1;
                     }
                     self.sim_updates_due -= updates_done as f32;
@@ -333,10 +349,12 @@ impl ApplicationHandler for App {
 
                 if let Some(renderer_state) = &mut self.renderer_state
                     && let Some(world) = &mut self.world
+                    && let Some(rb_sim_manager) = &mut self.rb_sim_manager
                     && let Some(camera) = &mut self.camera
                 {
                     renderer_state.render(
                         world,
+                        rb_sim_manager,
                         camera,
                         &mut self.config,
                         &self.diagnostics,
diff --git a/src/renderer/mod.rs b/src/renderer/mod.rs
index 5231bc3..e022fe7 100644
--- a/src/renderer/mod.rs
+++ b/src/renderer/mod.rs
@@ -2,6 +2,7 @@ mod ui;
 
 use std::sync::Arc;
 
+use fxhash::FxHashMap;
 use winit::window::Window;
 
 use crate::{
@@ -9,7 +10,7 @@ use crate::{
     camera::Camera,
     config::{CELLS_IN_CHUNK, CHUNK_SIZE},
     renderer::ui::draw_egui,
-    sim::world::World,
+    sim::{cell_sim::world::World, rb_sim::RbSimManager},
 };
 
 struct RendererChunk {
@@ -17,6 +18,11 @@ struct RendererChunk {
     bind_group: wgpu::BindGroup,
 }
 
+struct RendererRbEntity {
+    texture: wgpu::Texture,
+    bind_group: wgpu::BindGroup,
+}
+
 #[repr(C)]
 #[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
 struct ChunkData {
@@ -42,6 +48,8 @@ pub struct RendererState {
     pixels_pipeline: wgpu::RenderPipeline,
     camera_uniform_buffer: wgpu::Buffer,
     camera_uniform_bind_group: wgpu::BindGroup,
+
+    renderer_rb_entities: FxHashMap<u32, RendererRbEntity>,
 }
 
 impl RendererState {
@@ -270,6 +278,8 @@ impl RendererState {
             pixels_pipeline,
             camera_uniform_bind_group,
             camera_uniform_buffer,
+
+            renderer_rb_entities: FxHashMap::default(),
         }
     }
 
@@ -285,6 +295,7 @@ impl RendererState {
     pub fn render(
         &mut self,
         world: &mut World,
+        rb_sim_manager: &RbSimManager,
         camera: &mut Camera,
         config: &mut Config,
         diagnostics: &Diagnostics,
@@ -420,81 +431,192 @@ impl RendererState {
         }
 
         {
-            puffin::profile_scope!("Main render pass");
-            let mut render_pass: wgpu::RenderPass<'_> =
-                encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
-                    label: Some("Render Pass"),
-                    color_attachments: &[Some(wgpu::RenderPassColorAttachment {
-                        view: &view,
-                        resolve_target: None,
-                        depth_slice: None,
-                        ops: wgpu::Operations {
-                            load: wgpu::LoadOp::Clear(wgpu::Color {
-                                r: 0.0,
-                                g: 0.0,
-                                b: 0.0,
-                                a: 1.0,
-                            }),
-                            store: wgpu::StoreOp::Store,
+            puffin::profile_scope!("Upload entity textures");
+            for entity in rb_sim_manager.rb_entities.values() {
+                // TODO add "needs texture update"?
+
+                // TODO use material palette to improve bandwidth of upload
+                for i in 0..CELLS_IN_CHUNK {
+                    let material = entity.cells[i].material.def();
+                    chunk_buffer[i * 4] = material.color.0;
+                    chunk_buffer[i * 4 + 1] = material.color.1;
+                    chunk_buffer[i * 4 + 2] = material.color.2;
+                    chunk_buffer[i * 4 + 3] = material.color.3;
+                }
+
+                let render_entity = &self.renderer_rb_entities.entry(entity.id).or_insert({
+                    let texture = self.device.create_texture(&wgpu::TextureDescriptor {
+                        label: None,
+                        mip_level_count: 1,
+                        sample_count: 1,
+                        usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
+                        format: wgpu_types::TextureFormat::Rgba8UnormSrgb,
+                        size: wgpu::Extent3d {
+                            width: CHUNK_SIZE as u32,
+                            height: CHUNK_SIZE as u32,
+                            depth_or_array_layers: 1,
                         },
-                    })],
-                    depth_stencil_attachment: None,
-                    occlusion_query_set: None,
-                    timestamp_writes: None,
-                    multiview_mask: None,
+                        dimension: wgpu::TextureDimension::D2,
+                        view_formats: &[],
+                    });
+
+                    let bind_group_layout =
+                        self.device
+                            .create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+                                label: None,
+                                entries: &[wgpu::BindGroupLayoutEntry {
+                                    ty: wgpu::BindingType::Texture {
+                                        sample_type: wgpu::TextureSampleType::Float {
+                                            filterable: true,
+                                        },
+                                        view_dimension: wgpu::TextureViewDimension::D2,
+                                        multisampled: false,
+                                    },
+                                    binding: 0,
+                                    count: None,
+                                    visibility: wgpu::ShaderStages::FRAGMENT,
+                                }],
+                            });
+
+                    let bind_group = self.device.create_bind_group(&wgpu::BindGroupDescriptor {
+                        label: None,
+                        layout: &bind_group_layout,
+                        entries: &[wgpu::BindGroupEntry {
+                            binding: 0,
+                            resource: wgpu::BindingResource::TextureView(&texture.create_view(
+                                &wgpu::TextureViewDescriptor {
+                                    dimension: Some(wgpu::TextureViewDimension::D2),
+                                    usage: Some(
+                                        wgpu::TextureUsages::TEXTURE_BINDING
+                                            | wgpu::TextureUsages::COPY_DST,
+                                    ),
+                                    ..wgpu::TextureViewDescriptor::default()
+                                },
+                            )),
+                        }],
+                    });
+
+                    RendererRbEntity {
+                        texture,
+                        bind_group,
+                    }
                 });
 
-            render_pass.set_pipeline(&self.pixels_pipeline);
+                self.queue.write_texture(
+                    wgpu::TexelCopyTextureInfo {
+                        texture: &render_entity.texture,
+                        aspect: wgpu::TextureAspect::All,
+                        mip_level: 0,
+                        origin: wgpu::Origin3d::ZERO,
+                    },
+                    &chunk_buffer,
+                    wgpu::TexelCopyBufferLayout {
+                        bytes_per_row: Some(CHUNK_SIZE as u32 * 4),
+                        offset: 0,
+                        rows_per_image: Some(CHUNK_SIZE as u32),
+                    },
+                    wgpu::Extent3d {
+                        width: CHUNK_SIZE as u32,
+                        height: CHUNK_SIZE as u32,
+                        depth_or_array_layers: 1,
+                    },
+                );
+            }
+
+            {
+                puffin::profile_scope!("Main render pass");
+                let mut render_pass: wgpu::RenderPass<'_> =
+                    encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                        label: Some("Render Pass"),
+                        color_attachments: &[Some(wgpu::RenderPassColorAttachment {
+                            view: &view,
+                            resolve_target: None,
+                            depth_slice: None,
+                            ops: wgpu::Operations {
+                                load: wgpu::LoadOp::Clear(wgpu::Color {
+                                    r: 0.0,
+                                    g: 0.0,
+                                    b: 0.0,
+                                    a: 1.0,
+                                }),
+                                store: wgpu::StoreOp::Store,
+                            },
+                        })],
+                        depth_stencil_attachment: None,
+                        occlusion_query_set: None,
+                        timestamp_writes: None,
+                        multiview_mask: None,
+                    });
 
-            render_pass.set_bind_group(0, &self.camera_uniform_bind_group, &[]);
+                render_pass.set_pipeline(&self.pixels_pipeline);
 
-            let (xl, xu, yl, yu) = camera.viewport_bounds_world();
-            let ((cxl, cyl), _) = World::split_game_position(xl.floor() as i32, yl.floor() as i32);
-            let ((cxu, cyu), _) = World::split_game_position(xu.floor() as i32, yu.floor() as i32);
+                render_pass.set_bind_group(0, &self.camera_uniform_bind_group, &[]);
 
-            // TODO only visible chunks
-            for cx in cxl..=cxu {
-                for cy in cyl..=cyu {
-                    if let Some(idx) = world.chunk_position_to_chunk_idx.get(&(cx, cy)) {
-                        let render_chunk = &self.renderer_chunks[*idx];
-                        render_pass.set_bind_group(1, &render_chunk.bind_group, &[]);
-                        render_pass
-                            .set_immediates(0, bytemuck::bytes_of(&ChunkData { origin: [cx, cy] }));
-                        render_pass.draw(0..4, 0..1);
+                let (xl, xu, yl, yu) = camera.viewport_bounds_world();
+                let ((cxl, cyl), _) =
+                    World::split_game_position(xl.floor() as i32, yl.floor() as i32);
+                let ((cxu, cyu), _) =
+                    World::split_game_position(xu.floor() as i32, yu.floor() as i32);
+
+                for cx in cxl..=cxu {
+                    for cy in cyl..=cyu {
+                        if let Some(idx) = world.chunk_position_to_chunk_idx.get(&(cx, cy)) {
+                            let render_chunk = &self.renderer_chunks[*idx];
+                            render_pass.set_bind_group(1, &render_chunk.bind_group, &[]);
+                            render_pass.set_immediates(
+                                0,
+                                bytemuck::bytes_of(&ChunkData { origin: [cx, cy] }),
+                            );
+                            render_pass.draw(0..4, 0..1);
+                        }
                     }
                 }
+
+                // TODO this is inefficient
+                for rb_entity in rb_sim_manager.rb_entities.keys() {
+                    let renderer_rb_entity = self.renderer_rb_entities.get(rb_entity).unwrap();
+                    let (x, y) = rb_sim_manager.get_rb_entity_position(*rb_entity).unwrap();
+                    render_pass.set_bind_group(1, &renderer_rb_entity.bind_group, &[]);
+                    render_pass.set_immediates(
+                        0,
+                        bytemuck::bytes_of(&ChunkData {
+                            origin: [x.round() as i32, y.round() as i32],
+                        }),
+                    );
+                    render_pass.draw(0..4, 0..1);
+                }
             }
-        }
 
-        {
-            puffin::profile_scope!("Egui render pass");
-            let mut egui_pass = encoder
-                .begin_render_pass(&wgpu::RenderPassDescriptor {
-                    label: Some("egui pass"),
-                    color_attachments: &[Some(wgpu::RenderPassColorAttachment {
-                        view: &view,
-                        resolve_target: None,
-                        depth_slice: None,
-                        ops: wgpu::Operations {
-                            load: wgpu::LoadOp::Load,
-                            store: wgpu::StoreOp::Store,
-                        },
-                    })],
-                    depth_stencil_attachment: None,
-                    timestamp_writes: None,
-                    occlusion_query_set: None,
-                    multiview_mask: None,
-                })
-                .forget_lifetime();
+            {
+                puffin::profile_scope!("Egui render pass");
+                let mut egui_pass = encoder
+                    .begin_render_pass(&wgpu::RenderPassDescriptor {
+                        label: Some("egui pass"),
+                        color_attachments: &[Some(wgpu::RenderPassColorAttachment {
+                            view: &view,
+                            resolve_target: None,
+                            depth_slice: None,
+                            ops: wgpu::Operations {
+                                load: wgpu::LoadOp::Load,
+                                store: wgpu::StoreOp::Store,
+                            },
+                        })],
+                        depth_stencil_attachment: None,
+                        timestamp_writes: None,
+                        occlusion_query_set: None,
+                        multiview_mask: None,
+                    })
+                    .forget_lifetime();
 
-            self.egui_renderer
-                .render(&mut egui_pass, &clipped_primitives, &screen_descriptor);
-        }
+                self.egui_renderer
+                    .render(&mut egui_pass, &clipped_primitives, &screen_descriptor);
+            }
 
-        {
-            puffin::profile_scope!("Submit queue and present");
-            self.queue.submit(std::iter::once(encoder.finish()));
-            output.present();
+            {
+                puffin::profile_scope!("Submit queue and present");
+                self.queue.submit(std::iter::once(encoder.finish()));
+                output.present();
+            }
         }
     }
 }
diff --git a/src/renderer/ui.rs b/src/renderer/ui.rs
index 2e4ebc4..77af59d 100644
--- a/src/renderer/ui.rs
+++ b/src/renderer/ui.rs
@@ -2,7 +2,7 @@ use egui::{Color32, Stroke, Ui, epaint::CircleShape};
 
 use crate::{
     Camera, Config, Diagnostics, Input,
-    sim::{materials::MaterialId, world::World},
+    sim::{cell::materials::MaterialId, cell_sim::world::World},
 };
 
 pub fn draw_egui<'a>(
diff --git a/src/sim/cell.rs b/src/sim/cell/cell.rs
index d3ca302..d35fa76 100644
--- a/src/sim/cell.rs
+++ b/src/sim/cell/cell.rs
@@ -1,4 +1,4 @@
-use crate::sim::materials::MaterialId;
+use crate::sim::cell::materials::MaterialId;
 
 #[derive(Clone, Copy)]
 pub struct Cell {
diff --git a/src/sim/materials/fire.rs b/src/sim/cell/materials/fire.rs
index 97027d5..e0416b0 100644
--- a/src/sim/materials/fire.rs
+++ b/src/sim/cell/materials/fire.rs
@@ -1,6 +1,9 @@
 use rand::RngExt;
 
-use crate::sim::{cell::Cell, materials::MaterialId, sim::UpdateCtx};
+use crate::sim::{
+    cell::{cell::Cell, materials::MaterialId},
+    cell_sim::sim::UpdateCtx,
+};
 
 trait FireCellView {
     fn get_ticks_lived(self) -> u16;
diff --git a/src/sim/materials/gas.rs b/src/sim/cell/materials/gas.rs
index 8d9f42b..c0cd9f9 100644
--- a/src/sim/materials/gas.rs
+++ b/src/sim/cell/materials/gas.rs
@@ -1,4 +1,4 @@
-use crate::sim::sim::UpdateCtx;
+use crate::sim::cell_sim::sim::UpdateCtx;
 
 #[inline]
 pub fn sim_update(ctx: &mut UpdateCtx) {
diff --git a/src/sim/materials/mod.rs b/src/sim/cell/materials/mod.rs
index 10f0a06..a55ed51 100644
--- a/src/sim/materials/mod.rs
+++ b/src/sim/cell/materials/mod.rs
@@ -1,4 +1,4 @@
-use crate::sim::sim::UpdateCtx;
+use crate::sim::cell_sim::sim::UpdateCtx;
 
 mod fire;
 mod gas;
diff --git a/src/sim/materials/sand.rs b/src/sim/cell/materials/sand.rs
index ac8889f..d2d1265 100644
--- a/src/sim/materials/sand.rs
+++ b/src/sim/cell/materials/sand.rs
@@ -1,4 +1,4 @@
-use crate::sim::sim::UpdateCtx;
+use crate::sim::cell_sim::sim::UpdateCtx;
 
 #[inline]
 pub fn sim_update(ctx: &mut UpdateCtx) {
diff --git a/src/sim/materials/smoke.rs b/src/sim/cell/materials/smoke.rs
index 5240bc9..2ee7c00 100644
--- a/src/sim/materials/smoke.rs
+++ b/src/sim/cell/materials/smoke.rs
@@ -1,6 +1,6 @@
 use rand::RngExt;
 
-use crate::sim::sim::UpdateCtx;
+use crate::sim::cell_sim::sim::UpdateCtx;
 
 #[inline]
 pub fn sim_update(ctx: &mut UpdateCtx) {
diff --git a/src/sim/materials/water.rs b/src/sim/cell/materials/water.rs
index 1ba8eb4..4b848fb 100644
--- a/src/sim/materials/water.rs
+++ b/src/sim/cell/materials/water.rs
@@ -1,4 +1,4 @@
-use crate::sim::sim::UpdateCtx;
+use crate::sim::cell_sim::sim::UpdateCtx;
 
 #[inline]
 pub fn sim_update(ctx: &mut UpdateCtx) {
diff --git a/src/sim/cell/mod.rs b/src/sim/cell/mod.rs
new file mode 100644
index 0000000..2d2175c
--- /dev/null
+++ b/src/sim/cell/mod.rs
@@ -0,0 +1,2 @@
+pub mod cell;
+pub mod materials;
diff --git a/src/sim/chunk.rs b/src/sim/cell_sim/chunk.rs
index 478af12..116a38a 100644
--- a/src/sim/chunk.rs
+++ b/src/sim/cell_sim/chunk.rs
@@ -1,6 +1,6 @@
 use crate::{
     config::{CELLS_IN_CHUNK, CHUNK_SIZE},
-    sim::cell::Cell,
+    sim::cell::cell::Cell,
 };
 
 pub struct Chunk {
diff --git a/src/sim/cell_sim/mod.rs b/src/sim/cell_sim/mod.rs
new file mode 100644
index 0000000..a1db2a1
--- /dev/null
+++ b/src/sim/cell_sim/mod.rs
@@ -0,0 +1,4 @@
+pub mod chunk;
+pub mod overlay;
+pub mod sim;
+pub mod world;
diff --git a/src/sim/overlay.rs b/src/sim/cell_sim/overlay.rs
index c9fdf17..ee494ae 100644
--- a/src/sim/overlay.rs
+++ b/src/sim/cell_sim/overlay.rs
@@ -1,4 +1,4 @@
-use crate::{Config, Input, sim::world::World};
+use crate::{Config, Input, sim::cell_sim::world::World};
 
 pub fn create_compute_combined_overlay_offset(
     world: &World,
diff --git a/src/sim/sim.rs b/src/sim/cell_sim/sim.rs
index b9f4b76..fd9b6c9 100644
--- a/src/sim/sim.rs
+++ b/src/sim/cell_sim/sim.rs
@@ -6,7 +6,10 @@ use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
 
 use crate::{
     config::CHUNK_SIZE,
-    sim::{cell::Cell, chunk::Chunk, materials::MaterialDef, world::World},
+    sim::{
+        cell::{cell::Cell, materials::MaterialDef},
+        cell_sim::{chunk::Chunk, world::World},
+    },
 };
 
 struct ChunkAccess<'a> {
diff --git a/src/sim/world.rs b/src/sim/cell_sim/world.rs
index d54906c..924639a 100644
--- a/src/sim/world.rs
+++ b/src/sim/cell_sim/world.rs
@@ -2,7 +2,7 @@ use fxhash::FxHashMap;
 
 use crate::{
     config::CHUNK_SIZE,
-    sim::{cell::Cell, chunk::Chunk},
+    sim::{cell::cell::Cell, cell_sim::chunk::Chunk},
 };
 
 pub struct World {
diff --git a/src/sim/mod.rs b/src/sim/mod.rs
index 7553f89..63a9c56 100644
--- a/src/sim/mod.rs
+++ b/src/sim/mod.rs
@@ -1,6 +1,3 @@
 pub mod cell;
-pub mod chunk;
-pub mod materials;
-pub mod overlay;
-pub mod sim;
-pub mod world;
+pub mod cell_sim;
+pub mod rb_sim;
diff --git a/src/sim/rb_sim/mod.rs b/src/sim/rb_sim/mod.rs
new file mode 100644
index 0000000..1818052
--- /dev/null
+++ b/src/sim/rb_sim/mod.rs
@@ -0,0 +1,131 @@
+pub mod rb_entity;
+
+use fxhash::FxHashMap;
+use rapier2d::{
+    dynamics::{self},
+    geometry,
+    glamx::vec2,
+    math, prelude,
+};
+
+use crate::{
+    config::{CELLS_IN_CHUNK, PHYSICS_DELTA_TIME},
+    sim::{
+        cell::{cell::Cell, materials::MaterialId},
+        rb_sim::rb_entity::RbEntity,
+    },
+};
+
+pub struct PhysicsManager {
+    rigid_body_set: prelude::RigidBodySet,
+    collider_set: prelude::ColliderSet,
+    physics_pipeline: prelude::PhysicsPipeline,
+    integration_parameters: prelude::IntegrationParameters,
+    island_manager: prelude::IslandManager,
+    broad_phase: prelude::DefaultBroadPhase,
+    narrow_phase: prelude::NarrowPhase,
+    impulse_joint_set: prelude::ImpulseJointSet,
+    multibody_joint_set: prelude::MultibodyJointSet,
+    ccd_solver: prelude::CCDSolver,
+}
+
+impl PhysicsManager {
+    pub fn new() -> Self {
+        PhysicsManager {
+            rigid_body_set: prelude::RigidBodySet::new(),
+            collider_set: prelude::ColliderSet::new(),
+            physics_pipeline: prelude::PhysicsPipeline::new(),
+            integration_parameters: prelude::IntegrationParameters {
+                // 20 pixels = 1 meter
+                length_unit: 20.0,
+                dt: PHYSICS_DELTA_TIME,
+                ..prelude::IntegrationParameters::default()
+            },
+            island_manager: prelude::IslandManager::new(),
+            broad_phase: prelude::DefaultBroadPhase::new(),
+            narrow_phase: prelude::NarrowPhase::new(),
+            impulse_joint_set: prelude::ImpulseJointSet::new(),
+            multibody_joint_set: prelude::MultibodyJointSet::new(),
+            ccd_solver: prelude::CCDSolver::new(),
+        }
+    }
+}
+
+pub struct RbSimManager {
+    physics_manager: PhysicsManager,
+    pub rb_entities: FxHashMap<u32, RbEntity>,
+}
+
+impl RbSimManager {
+    pub fn rb_tick(&mut self, delta_time: f32) {
+        let gravity = vec2(0.0, -9.81);
+
+        self.physics_manager.physics_pipeline.step(
+            gravity,
+            &self.physics_manager.integration_parameters,
+            &mut self.physics_manager.island_manager,
+            &mut self.physics_manager.broad_phase,
+            &mut self.physics_manager.narrow_phase,
+            &mut self.physics_manager.rigid_body_set,
+            &mut self.physics_manager.collider_set,
+            &mut self.physics_manager.impulse_joint_set,
+            &mut self.physics_manager.multibody_joint_set,
+            &mut self.physics_manager.ccd_solver,
+            &(),
+            &(),
+        );
+    }
+
+    pub fn get_rb_entity_position(&self, entity_id: u32) -> Option<(f32, f32)> {
+        let entity = self.rb_entities.get(&entity_id);
+        match entity {
+            Some(entity) => {
+                let rb = self.physics_manager.rigid_body_set.get(entity.rb_parent);
+                rb.map(|rb| (rb.position().translation.x, rb.position().translation.y))
+            }
+            None => return None,
+        }
+    }
+
+    pub fn test(&mut self) {
+        /* Create the ground. */
+        let collider = geometry::ColliderBuilder::cuboid(100.0, 0.1).build();
+        self.physics_manager.collider_set.insert(collider);
+
+        /* Create the bouncing ball. */
+        let rigid_body = dynamics::RigidBodyBuilder::dynamic()
+            .translation(math::Vector::new(0.0, 10.0))
+            .build();
+        let collider = geometry::ColliderBuilder::ball(0.5)
+            .restitution(0.7)
+            .build();
+        let ball_body_handle = self.physics_manager.rigid_body_set.insert(rigid_body);
+        self.physics_manager.collider_set.insert_with_parent(
+            collider,
+            ball_body_handle,
+            &mut self.physics_manager.rigid_body_set,
+        );
+
+        let test_cells = Box::new([Cell::void(); CELLS_IN_CHUNK]);
+        let mut rb_entity = RbEntity {
+            id: 0,
+            cells: test_cells,
+            rb_parent: ball_body_handle,
+        };
+
+        for x in 0..10 {
+            for y in 0..10 {
+                rb_entity.set_cell_at_local_position(x, y, Cell::from_material(MaterialId::Wood));
+            }
+        }
+
+        self.rb_entities.insert(0, rb_entity);
+    }
+
+    pub fn new() -> Self {
+        RbSimManager {
+            physics_manager: PhysicsManager::new(),
+            rb_entities: FxHashMap::default(),
+        }
+    }
+}
diff --git a/src/sim/rb_sim/rb_entity.rs b/src/sim/rb_sim/rb_entity.rs
new file mode 100644
index 0000000..50243bc
--- /dev/null
+++ b/src/sim/rb_sim/rb_entity.rs
@@ -0,0 +1,24 @@
+use rapier2d::prelude;
+
+use crate::{
+    config::{CELLS_IN_CHUNK, CHUNK_SIZE},
+    sim::cell::cell::Cell,
+};
+
+pub struct RbEntity {
+    pub id: u32,
+    // TODO resizable
+    pub cells: Box<[Cell; CELLS_IN_CHUNK]>,
+    pub rb_parent: prelude::RigidBodyHandle,
+}
+
+impl RbEntity {
+    #[inline]
+    pub fn get_cell_at_local_position(&self, x: u8, y: u8) -> Cell {
+        self.cells[x as usize + y as usize * CHUNK_SIZE as usize]
+    }
+    #[inline]
+    pub fn set_cell_at_local_position(&mut self, x: u8, y: u8, cell: Cell) {
+        self.cells[x as usize + y as usize * CHUNK_SIZE as usize] = cell;
+    }
+}