Add physics engine integration with rapier3d

Cargo.lock

@@ -55,6 +55,12 @@ dependencies = [
  "equator",
 ]
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
+
 [[package]]
 name = "android-activity"
 version = "0.6.0"
@@ -73,7 +79,7 @@ dependencies = [
  "ndk-context",
  "ndk-sys",
  "num_enum",
- "thiserror",
+ "thiserror 1.0.69",
 ]
 
 [[package]]
@@ -88,6 +94,15 @@ version = "1.0.98"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e16d2d3311acee920a9eb8d33b8cbc1787ce4a264e85f964c2404b969bdcd487"
 
+[[package]]
+name = "approx"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cab112f0a86d568ea0e627cc1d6be74a1e9cd55214684db5561995f6dad897c6"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "arbitrary"
 version = "1.4.1"
@@ -179,6 +194,12 @@ version = "0.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9e1b586273c5702936fe7b7d6896644d8be71e6314cfe09d3167c95f712589e8"
 
+[[package]]
+name = "bit-vec"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e764a1d40d510daf35e07be9eb06e75770908c27d411ee6c92109c9840eaaf7"
+
 [[package]]
 name = "bit_field"
 version = "0.10.2"
@@ -259,7 +280,7 @@ dependencies = [
  "polling",
  "rustix 0.38.44",
  "slab",
- "thiserror",
+ "thiserror 1.0.69",
 ]
 
 [[package]]
@@ -402,6 +423,28 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "crossbeam"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1137cd7e7fc0fb5d3c5a8678be38ec56e819125d8d7907411fe24ccb943faca8"
+dependencies = [
+ "crossbeam-channel",
+ "crossbeam-deque",
+ "crossbeam-epoch",
+ "crossbeam-queue",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-channel"
+version = "0.5.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "82b8f8f868b36967f9606790d1903570de9ceaf870a7bf9fbbd3016d636a2cb2"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-deque"
 version = "0.8.6"
@@ -421,6 +464,15 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "crossbeam-queue"
+version = "0.3.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0f58bbc28f91df819d0aa2a2c00cd19754769c2fad90579b3592b1c9ba7a3115"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-utils"
 version = "0.8.21"
@@ -470,6 +522,12 @@ version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "75b325c5dbd37f80359721ad39aca5a29fb04c89279657cffdda8736d0c0b9d2"
 
+[[package]]
+name = "downcast-rs"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea8a8b81cacc08888170eef4d13b775126db426d0b348bee9d18c2c1eaf123cf"
+
 [[package]]
 name = "dpi"
 version = "0.1.2"
@@ -482,6 +540,15 @@ version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
 
+[[package]]
+name = "ena"
+version = "0.14.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d248bdd43ce613d87415282f69b9bb99d947d290b10962dd6c56233312c2ad5"
+dependencies = [
+ "log",
+]
+
 [[package]]
 name = "equator"
 version = "0.4.2"
@@ -558,6 +625,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "foreign-types"
 version = "0.5.0"
@@ -599,6 +672,7 @@ dependencies = [
  "imgui",
  "imgui-glium-renderer",
  "imgui-winit-support",
+ "rapier3d",
  "winit",
 ]
 
@@ -800,6 +874,15 @@ dependencies = [
  "crunchy",
 ]
 
+[[package]]
+name = "hash32"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47d60b12902ba28e2730cd37e95b8c9223af2808df9e902d4df49588d1470606"
+dependencies = [
+ "byteorder",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.14.5"
@@ -814,6 +897,21 @@ name = "hashbrown"
 version = "0.15.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5971ac85611da7067dbfcabef3c70ebb5606018acd9e2a3903a0da507521e0d5"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash",
+]
+
+[[package]]
+name = "heapless"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0bfb9eb618601c89945a70e254898da93b13be0388091d42117462b265bb3fad"
+dependencies = [
+ "hash32",
+ "stable_deref_trait",
+]
 
 [[package]]
 name = "heck"
@@ -974,7 +1072,7 @@ dependencies = [
  "combine",
  "jni-sys",
  "log",
- "thiserror",
+ "thiserror 1.0.69",
  "walkdir",
  "windows-sys 0.45.0",
 ]
@@ -1055,6 +1153,12 @@ dependencies = [
  "windows-targets 0.53.2",
 ]
 
+[[package]]
+name = "libm"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f9fbbcab51052fe104eb5e5d351cf728d30a5be1fe14d9be8a3b097481fb97de"
+
 [[package]]
 name = "libredox"
 version = "0.1.3"
@@ -1103,6 +1207,16 @@ dependencies = [
  "imgref",
 ]
 
+[[package]]
+name = "matrixmultiply"
+version = "0.3.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a06de3016e9fae57a36fd14dba131fccf49f74b40b7fbdb472f96e361ec71a08"
+dependencies = [
+ "autocfg",
+ "rawpointer",
+]
+
 [[package]]
 name = "maybe-rayon"
 version = "0.1.1"
@@ -1159,6 +1273,33 @@ version = "0.5.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e53debba6bda7a793e5f99b8dacf19e626084f525f7829104ba9898f367d85ff"
 
+[[package]]
+name = "nalgebra"
+version = "0.33.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "26aecdf64b707efd1310e3544d709c5c0ac61c13756046aaaba41be5c4f66a3b"
+dependencies = [
+ "approx",
+ "matrixmultiply",
+ "nalgebra-macros",
+ "num-complex",
+ "num-rational",
+ "num-traits",
+ "simba",
+ "typenum",
+]
+
+[[package]]
+name = "nalgebra-macros"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "254a5372af8fc138e36684761d3c0cdb758a4410e938babcff1c860ce14ddbfc"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "ndk"
 version = "0.9.0"
@@ -1171,7 +1312,7 @@ dependencies = [
  "ndk-sys",
  "num_enum",
  "raw-window-handle",
- "thiserror",
+ "thiserror 1.0.69",
 ]
 
 [[package]]
@@ -1221,6 +1362,15 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "num-complex"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73f88a1307638156682bada9d7604135552957b7818057dcef22705b4d509495"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "num-derive"
 version = "0.4.2"
@@ -1259,6 +1409,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
 dependencies = [
  "autocfg",
+ "libm",
 ]
 
 [[package]]
@@ -1553,6 +1704,15 @@ dependencies = [
  "libredox",
 ]
 
+[[package]]
+name = "ordered-float"
+version = "5.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2c1f9f56e534ac6a9b8a4600bdf0f530fb393b5f393e7b4d03489c3cf0c3f01"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "owned_ttf_parser"
 version = "0.25.0"
@@ -1585,6 +1745,31 @@ dependencies = [
  "windows-targets 0.52.6",
 ]
 
+[[package]]
+name = "parry3d"
+version = "0.21.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e7f8d0a3b2f4c0e250d4599b69e490535521c3497e2b88b0b5d2ada251bc83a8"
+dependencies = [
+ "approx",
+ "arrayvec",
+ "bitflags 2.9.1",
+ "downcast-rs 2.0.1",
+ "either",
+ "ena",
+ "hashbrown 0.15.4",
+ "log",
+ "nalgebra",
+ "num-derive",
+ "num-traits",
+ "ordered-float",
+ "rstar",
+ "simba",
+ "slab",
+ "spade",
+ "thiserror 2.0.12",
+]
+
 [[package]]
 name = "paste"
 version = "1.0.15"
@@ -1772,6 +1957,30 @@ dependencies = [
  "getrandom 0.2.16",
 ]
 
+[[package]]
+name = "rapier3d"
+version = "0.26.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f1015500058823ba9c479c908d7069adcf3f0f51a3e49dca7efc5575df7e574"
+dependencies = [
+ "approx",
+ "arrayvec",
+ "bit-vec",
+ "bitflags 2.9.1",
+ "crossbeam",
+ "downcast-rs 2.0.1",
+ "log",
+ "nalgebra",
+ "num-derive",
+ "num-traits",
+ "ordered-float",
+ "parry3d",
+ "profiling",
+ "rustc-hash",
+ "simba",
+ "thiserror 2.0.12",
+]
+
 [[package]]
 name = "rav1e"
 version = "0.7.1"
@@ -1802,7 +2011,7 @@ dependencies = [
  "rand_chacha",
  "simd_helpers",
  "system-deps",
- "thiserror",
+ "thiserror 1.0.69",
  "v_frame",
  "wasm-bindgen",
 ]
@@ -1828,6 +2037,12 @@ version = "0.6.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "20675572f6f24e9e76ef639bc5552774ed45f1c30e2951e1e99c59888861c539"
 
+[[package]]
+name = "rawpointer"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60a357793950651c4ed0f3f52338f53b2f809f32d83a07f72909fa13e4c6c1e3"
+
 [[package]]
 name = "rayon"
 version = "1.10.0"
@@ -1872,12 +2087,35 @@ version = "0.8.50"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "57397d16646700483b67d2dd6511d79318f9d057fdbd21a4066aeac8b41d310a"
 
+[[package]]
+name = "robust"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e27ee8bb91ca0adcf0ecb116293afa12d393f9c2b9b9cd54d33e8078fe19839"
+
+[[package]]
+name = "rstar"
+version = "0.12.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "421400d13ccfd26dfa5858199c30a5d76f9c54e0dba7575273025b43c5175dbb"
+dependencies = [
+ "heapless",
+ "num-traits",
+ "smallvec",
+]
+
 [[package]]
 name = "rustc-demangle"
 version = "0.1.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "989e6739f80c4ad5b13e0fd7fe89531180375b18520cc8c82080e4dc4035b84f"
 
+[[package]]
+name = "rustc-hash"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "357703d41365b4b27c590e3ed91eabb1b663f07c4c084095e60cbed4362dff0d"
+
 [[package]]
 name = "rustix"
 version = "0.38.44"
@@ -1916,6 +2154,15 @@ version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "28d3b2b1366ec20994f1fd18c3c594f05c5dd4bc44d8bb0c1c632c8d6829481f"
 
+[[package]]
+name = "safe_arch"
+version = "0.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96b02de82ddbe1b636e6170c21be622223aea188ef2e139be0a5b219ec215323"
+dependencies = [
+ "bytemuck",
+]
+
 [[package]]
 name = "same-file"
 version = "1.0.6"
@@ -1997,6 +2244,19 @@ version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
 
+[[package]]
+name = "simba"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b3a386a501cd104797982c15ae17aafe8b9261315b5d07e3ec803f2ea26be0fa"
+dependencies = [
+ "approx",
+ "num-complex",
+ "num-traits",
+ "paste",
+ "wide",
+]
+
 [[package]]
 name = "simd-adler32"
 version = "0.3.7"
@@ -2038,7 +2298,7 @@ dependencies = [
  "log",
  "memmap2",
  "rustix 0.38.44",
- "thiserror",
+ "thiserror 1.0.69",
  "wayland-backend",
  "wayland-client",
  "wayland-csd-frame",
@@ -2058,12 +2318,30 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "spade"
+version = "2.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a14e31a007e9f85c32784b04f89e6e194bb252a4d41b4a8ccd9e77245d901c8c"
+dependencies = [
+ "hashbrown 0.15.4",
+ "num-traits",
+ "robust",
+ "smallvec",
+]
+
 [[package]]
 name = "spin"
 version = "0.9.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
 
+[[package]]
+name = "stable_deref_trait"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a8f112729512f8e442d81f95a8a7ddf2b7c6b8a1a6f509a95864142b30cab2d3"
+
 [[package]]
 name = "strict-num"
 version = "0.1.1"
@@ -2106,7 +2384,16 @@ version = "1.0.69"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6aaf5339b578ea85b50e080feb250a3e8ae8cfcdff9a461c9ec2904bc923f52"
 dependencies = [
- "thiserror-impl",
+ "thiserror-impl 1.0.69",
+]
+
+[[package]]
+name = "thiserror"
+version = "2.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "567b8a2dae586314f7be2a752ec7474332959c6460e02bde30d702a66d488708"
+dependencies = [
+ "thiserror-impl 2.0.12",
 ]
 
 [[package]]
@@ -2120,6 +2407,17 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thiserror-impl"
+version = "2.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f7cf42b4507d8ea322120659672cf1b9dbb93f8f2d4ecfd6e51350ff5b17a1d"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "tiff"
 version = "0.9.1"
@@ -2212,6 +2510,12 @@ version = "0.25.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d2df906b07856748fa3f6e0ad0cbaa047052d4a7dd609e231c4f72cee8c36f31"
 
+[[package]]
+name = "typenum"
+version = "1.18.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1dccffe3ce07af9386bfd29e80c0ab1a8205a2fc34e4bcd40364df902cfa8f3f"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.18"
@@ -2355,7 +2659,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fe770181423e5fc79d3e2a7f4410b7799d5aab1de4372853de3c6aa13ca24121"
 dependencies = [
  "cc",
- "downcast-rs",
+ "downcast-rs 1.2.1",
  "rustix 0.38.44",
  "scoped-tls",
  "smallvec",
@@ -2483,6 +2787,16 @@ version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a751b3277700db47d3e574514de2eced5e54dc8a5436a3bf7a0b248b2cee16f3"
 
+[[package]]
+name = "wide"
+version = "0.7.33"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ce5da8ecb62bcd8ec8b7ea19f69a51275e91299be594ea5cc6ef7819e16cd03"
+dependencies = [
+ "bytemuck",
+ "safe_arch",
+]
+
 [[package]]
 name = "winapi-util"
 version = "0.1.9"

Cargo.toml

@@ -19,3 +19,5 @@ imgui-winit-support = "0.13"
 imgui-glium-renderer = "0.13"
 
 winit = "0.30"
+
+rapier3d = "0.26.1"

src/main.rs

@@ -5,6 +5,7 @@ mod gltf_loader;
 mod render;
 mod time;
 mod ui;
+mod physics;
 
 use anyhow::Result;
 use camera::Camera;
@@ -12,6 +13,8 @@ use ecs::{Transform};
 use glam::{Quat, Vec3, EulerRot};
 use glium::backend::glutin::SimpleWindowBuilder;
 use render::GliumRenderer;
+use rapier3d::prelude::*;
+use rapier3d::na::{UnitQuaternion, Quaternion};
 
 fn main() -> Result<()> {
     let event_loop = glium::winit::event_loop::EventLoop::builder()
@@ -20,7 +23,7 @@ fn main() -> Result<()> {
 
     let (window, display) = SimpleWindowBuilder::new()
         .with_title("fps")
-        .with_inner_size(1280, 720)
+        .with_inner_size(1920, 1080)
         .build(&event_loop);
 
     // Create ECS renderer which internally owns both the world and the renderer
@@ -30,6 +33,8 @@ fn main() -> Result<()> {
         ecs::ECSRenderer::new(renderer, world)
     };
 
+    let mut physics = physics::Physics::new();
+
     // Dear ImGui integration
     let mut gui = ui::Gui::new(&display, &window)?;
 
@@ -38,7 +43,7 @@ fn main() -> Result<()> {
     let object_ent = {
         let model_3d = gltf_loader::load_gltf("resources/models/tree.gltf", &display)?;
         ecsr.spawn_mesh(model_3d, Transform {
-            translation: Vec3::new(0.0, -2.5, -5.0),
+            translation: Vec3::new(0.0, 2.5, -5.0),
             rotation:    Quat::IDENTITY,
             scale:       Vec3::new(0.01, 0.01, 0.01),
         })
@@ -49,10 +54,34 @@ fn main() -> Result<()> {
         ecsr.spawn_mesh(model_3d, Transform {
             translation: Vec3::new(0.0, -1.5, 0.0),
             rotation:    Quat::IDENTITY,
-            scale:       Vec3::new(1.0, 1.0, 1.0),
+            scale:       Vec3::new(10.0, 10.0, 10.0),
         })
     };
 
+    // Add physics for ground
+    let ground_tr = *ecsr.world.get::<&Transform>(ground_ent).unwrap();
+    let (axis, angle) = ground_tr.rotation.to_axis_angle();
+    let rotation = vector![axis.x * angle, axis.y * angle, axis.z * angle];
+    let ground_pos = Isometry::new(
+        vector![ground_tr.translation.x, ground_tr.translation.y, ground_tr.translation.z],
+        rotation,
+    );
+    let ground_rb = RigidBodyBuilder::fixed().position(ground_pos).build();
+    let ground_collider = ColliderBuilder::cuboid(10.0, 0.1, 10.0).build();
+    physics.add_rigid_body(ground_ent, ground_rb, ground_collider);
+
+    // Add physics for object
+    let object_tr = *ecsr.world.get::<&Transform>(object_ent).unwrap();
+    let (axis, angle) = object_tr.rotation.to_axis_angle();
+    let rotation = vector![axis.x * angle, axis.y * angle, axis.z * angle];
+    let object_pos = Isometry::new(
+        vector![object_tr.translation.x, object_tr.translation.y, object_tr.translation.z],
+        rotation,
+    );
+    let object_rb = RigidBodyBuilder::dynamic().position(object_pos).build();
+    let object_collider = ColliderBuilder::cylinder(2.0, 0.2).build();
+    physics.add_rigid_body(object_ent, object_rb, object_collider);
+
 
     let camera_ent = {
         let (w, h): (u32, u32) = window.inner_size().into();
@@ -117,6 +146,7 @@ fn main() -> Result<()> {
                 },
                 Event::AboutToWait => {
                     time.tick();
+                    physics.step(time.delta_seconds(), &mut ecsr.world);
                     gui.prepare_frame(&window);
                     window.request_redraw();
                 }

src/physics.rs

@@ -0,0 +1,90 @@
+use std::collections::HashMap;
+use rapier3d::prelude::*;
+use hecs::World;
+use glam::{Vec3, Quat};
+use crate::ecs::Transform;
+
+pub struct Physics {
+    rigid_bodies: RigidBodySet,
+    colliders: ColliderSet,
+    integration_params: IntegrationParameters,
+    pipeline: PhysicsPipeline,
+    island_manager: IslandManager,
+    broad_phase: BroadPhaseMultiSap,
+    narrow_phase: NarrowPhase,
+    impulse_joints: ImpulseJointSet,
+    multibody_joints: MultibodyJointSet,
+    ccd_solver: CCDSolver,
+    query_pipeline: QueryPipeline,
+    gravity: Vector<f32>,
+    entity_to_rb: HashMap<hecs::Entity, RigidBodyHandle>,
+}
+
+impl Physics {
+    pub fn new() -> Self {
+        let rigid_bodies = RigidBodySet::new();
+        let colliders = ColliderSet::new();
+        let integration_params = IntegrationParameters::default();
+        let pipeline = PhysicsPipeline::new();
+        let island_manager = IslandManager::new();
+        let broad_phase = BroadPhaseMultiSap::new();
+        let narrow_phase = NarrowPhase::new();
+        let impulse_joints = ImpulseJointSet::new();
+        let multibody_joints = MultibodyJointSet::new();
+        let ccd_solver = CCDSolver::new();
+        let query_pipeline = QueryPipeline::new();
+        let gravity = vector![0.0, -9.81, 0.0];
+        Self {
+            rigid_bodies,
+            colliders,
+            integration_params,
+            pipeline,
+            island_manager,
+            broad_phase,
+            narrow_phase,
+            impulse_joints,
+            multibody_joints,
+            ccd_solver,
+            query_pipeline,
+            gravity,
+            entity_to_rb: HashMap::new(),
+        }
+    }
+
+    pub fn step(&mut self, dt: f32, world: &mut World) {
+        let physics_hooks = ();
+        let event_handler = ();
+        self.integration_params.dt = dt;
+        self.pipeline.step(
+            &self.gravity,
+            &self.integration_params,
+            &mut self.island_manager,
+            &mut self.broad_phase,
+            &mut self.narrow_phase,
+            &mut self.rigid_bodies,
+            &mut self.colliders,
+            &mut self.impulse_joints,
+            &mut self.multibody_joints,
+            &mut self.ccd_solver,
+            Some(&mut self.query_pipeline),
+            &physics_hooks,
+            &event_handler,
+        );
+
+        for (&ent, &handle) in &self.entity_to_rb {
+            if let Ok(mut tr) = world.get::<&mut Transform>(ent) {
+                let rb = self.rigid_bodies.get(handle).unwrap();
+                let pos = rb.position();
+                tr.translation = Vec3::new(pos.translation.x, pos.translation.y, pos.translation.z);
+                let q = pos.rotation;
+                tr.rotation = Quat::from_xyzw(q.i, q.j, q.k, q.w);
+            }
+        }
+    }
+
+    pub fn add_rigid_body(&mut self, ent: hecs::Entity, rb: RigidBody, collider: Collider) {
+        let rb_handle = self.rigid_bodies.insert(rb);
+        self.colliders.insert_with_parent(collider, rb_handle, &mut self.rigid_bodies);
+        self.entity_to_rb.insert(ent, rb_handle);
+    }
+}