diff --git a/Sources/CppBackend/CMakeLists.txt b/Sources/CppBackend/CMakeLists.txt
index c0b8282..c118a0f 100644
--- a/Sources/CppBackend/CMakeLists.txt
+++ b/Sources/CppBackend/CMakeLists.txt
@@ -1,4 +1,4 @@
-add_library(CppBackend STATIC backend.h backend.cpp)
+add_library(CppBackend STATIC ball.hpp ball.cpp)
 set_property(TARGET CppBackend PROPERTY Swift_MODULE_NAME "CppBackend")
 set_property(TARGET CppBackend PROPERTY CXX_STANDARD 20)
 
diff --git a/Sources/CppBackend/backend.cpp b/Sources/CppBackend/backend.cpp
deleted file mode 100644
index 1917ed3..0000000
--- a/Sources/CppBackend/backend.cpp
+++ /dev/null
@@ -1,7 +0,0 @@
-#include "backend.h"
-
-#include <iostream>
-
-void backend_init() {
-  std::cout << "Hello World" << std::endl;
-}
diff --git a/Sources/CppBackend/backend.h b/Sources/CppBackend/backend.h
deleted file mode 100644
index 592be9d..0000000
--- a/Sources/CppBackend/backend.h
+++ /dev/null
@@ -1,3 +0,0 @@
-#pragma once
-
-void backend_init();
diff --git a/Sources/CppBackend/ball.cpp b/Sources/CppBackend/ball.cpp
new file mode 100644
index 0000000..6078a2b
--- /dev/null
+++ b/Sources/CppBackend/ball.cpp
@@ -0,0 +1,41 @@
+#include "ball.hpp"
+#include <cmath>
+
+
+Ball::Ball(vec2f pos, float angle, float ballSize) noexcept :
+  _position(pos),
+  _velocity(simd::make<vec2f>(
+     std::cos(angle * M_PI * 2.0f),
+    -std::sin(angle * M_PI * 2.0f)
+  )),
+  _size(ballSize) {
+}
+
+void Ball::update(float deltaTime) noexcept {
+  _position += _velocity * speed * deltaTime;
+  if (_position.x < _size) {
+    _velocity.x = -_velocity.x;
+    _position.x = _size;
+  } else if (_position.x > worldSize - _size) {
+    _velocity.x = -_velocity.x;
+    _position.x = worldSize - _size;
+  }
+  if (_position.y < _size) {
+    _velocity.y = -_velocity.y;
+    _position.y = _size;
+  } else if (_position.y > worldSize - _size) {
+    _velocity.y = -_velocity.y;
+    _position.y = worldSize - _size;
+  }
+}
+
+
+void BallWorld::add(Ball::vec2f pos, float angle, float ballSize) noexcept {
+  balls.emplace_back(Ball{ pos, angle, ballSize });
+}
+
+void BallWorld::update(float deltaTime) noexcept {
+  for (auto& ball : balls) {
+    ball.update(deltaTime);
+  }
+}
diff --git a/Sources/CppBackend/ball.hpp b/Sources/CppBackend/ball.hpp
new file mode 100644
index 0000000..7faca3d
--- /dev/null
+++ b/Sources/CppBackend/ball.hpp
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <simd/simd.h>
+#include <vector>
+
+struct Ball {
+  using vec2f = simd::float2;
+
+private:
+  constexpr static float speed = 80.0f;
+  constexpr static float worldSize = 512.0f;
+
+  vec2f _position, _velocity;
+  float _size;
+
+public:
+  Ball(vec2f pos, float angle, float ballSize) noexcept;
+  virtual ~Ball() noexcept = default;
+
+  void update(float deltaTime) noexcept;
+
+  [[nodiscard]] constexpr const vec2f& position() const noexcept {
+    return _position;
+  }
+  [[nodiscard]] constexpr const vec2f& velocity() const noexcept {
+    return _velocity;
+  }
+  [[nodiscard]] constexpr const float size() const noexcept {
+    return _size;
+  }
+};
+
+
+struct BallWorld {
+  std::vector<Ball> balls;
+
+  void add(Ball::vec2f pos, float angle, float ballSize) noexcept;
+  void update(float deltaTime) noexcept;
+};
diff --git a/Sources/CppBackend/module.modulemap b/Sources/CppBackend/module.modulemap
index 3b24d92..5361cb5 100644
--- a/Sources/CppBackend/module.modulemap
+++ b/Sources/CppBackend/module.modulemap
@@ -1,3 +1,3 @@
 module CppBackend {
-  header "backend.h"
+  header "ball.hpp"
 }
diff --git a/Sources/SwiftFrontend/Application.swift b/Sources/SwiftFrontend/Application.swift
index d47be0c..bb4f452 100644
--- a/Sources/SwiftFrontend/Application.swift
+++ b/Sources/SwiftFrontend/Application.swift
@@ -6,19 +6,26 @@
 //
 
 import Foundation
+import CppBackend
 import SDL3
 
 class Application {
   private var window: OpaquePointer? = nil
   private var renderer: OpaquePointer? = nil
 
+  private var balls = BallWorld()
+  private var lastCounter: UInt64 = 0
+
   private func initialize() -> ApplicationExecutionState {
     guard SDL_Init(SDL_INIT_VIDEO) >= 0 else {
       print("SDL_Init() error: \(String(cString: SDL_GetError()))")
       return .exitFailure
     }
 
-    window = SDL_CreateWindow("Hello World", 512, 512, 0)
+    let width: Int32 = 512, height: Int32 = 512
+    let sdlWindowResizable:        SDL_WindowFlags = 0x0000000000000020
+    let sdlWindowHighPixelDensity: SDL_WindowFlags = 0x0000000000002000
+    window = SDL_CreateWindow("Hello World", width, height, sdlWindowResizable | sdlWindowHighPixelDensity)
     guard window != nil else {
       print("SDL_CreateWindow() error: \(String(cString: SDL_GetError()))")
       return .exitFailure
@@ -29,6 +36,19 @@ class Application {
       print("SDL_CreateRenderer() error: \(String(cString: SDL_GetError()))")
       return .exitFailure
     }
+    SDL_SetRenderVSync(renderer, 1)
+    SDL_SetRenderLogicalPresentation(renderer, 512, 512, SDL_LOGICAL_PRESENTATION_LETTERBOX, SDL_SCALEMODE_BEST)
+
+    let ballOrigin = SIMD2(Float(width), Float(height)) * 0.5
+    for _ in 0..<10 {
+      balls.add(
+        ballOrigin,
+        Float(arc4random()) / Float(UInt32.max),
+        Float(arc4random_uniform(32 - 3) + 3)
+      )
+    }
+
+    lastCounter = SDL_GetPerformanceCounter()
 
     return .running
   }
@@ -58,16 +78,35 @@ class Application {
     }
   }
 
-  private func paint() -> ApplicationExecutionState {
+  private func paint(_ deltaTime: Float) -> ApplicationExecutionState {
+    balls.update(deltaTime)
+
     SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255)
     SDL_RenderClear(renderer)
-    var rect = SDL_FRect(x: 0, y: 0, w: 100, h: 100)
+
     SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255)
-    SDL_RenderFillRect(renderer, &rect)
+    for ball in balls.balls {
+      let position = ball.position().pointee, size = ball.size()
+      var rect = SDL_FRect(
+        x: position.x - size,
+        y: position.y - size,
+        w: size * 2.0,
+        h: size * 2.0
+      )
+      SDL_RenderFillRect(renderer, &rect)
+    }
+
     SDL_RenderPresent(renderer)
     return .running
   }
 
+  private func deltaTime() -> Double {
+    let counter = SDL_GetPerformanceCounter()
+    let divisor = 1.0 / Double(SDL_GetPerformanceFrequency())
+    defer { lastCounter = counter }
+    return Double(counter &- lastCounter) * divisor
+  }
+
   func run() -> Int32 {
     var res = initialize()
     quit: while res == .running {
@@ -78,7 +117,7 @@ class Application {
           break quit
         }
       }
-      res = paint()
+      res = paint(Float(deltaTime()))
     }
     return res == .exitSuccess ? 0 : 1
   }