Add a way to change FPS

README.md

@@ -135,7 +135,7 @@ int main(int argc, char **argv) {
 - [ ] Project metadata
 - [ ] Turbo mode
 - [ ] Multithreading (experimental)
-- [ ] Custom FPS in the default event loop (`libscratchcpp::Engine::run()`)
+- [x] Custom FPS in the default event loop (`libscratchcpp::Engine::run()`)
 - [ ] Scratch 2.0 to 3.0 converter (help needed)
 - [ ] Scratch 1.4 and below to 3.0 converter (help needed)
 - [ ] API for comments

include/scratchcpp/iengine.h

@@ -85,6 +85,12 @@ class LIBSCRATCHCPP_EXPORT IEngine
          */
         virtual void run() = 0;
 
+        /*! Returns the framerate of the project. */
+        virtual double fps() const = 0;
+
+        /*! Sets the framerate of the project. */
+        virtual void setFps(double fps) = 0;
+
         /*! Returns true if there are any running script of the broadcast with the given index. */
         virtual bool broadcastRunning(unsigned int index, VirtualMachine *sourceScript) = 0;
 

src/engine/internal/engine.cpp

@@ -317,7 +317,7 @@ void Engine::initClone(Sprite *clone)
 
 void Engine::run()
 {
-    auto frameDuration = std::chrono::milliseconds(33);
+    updateFrameDuration();
     start();
 
     while (true) {
@@ -332,7 +332,7 @@ void Engine::run()
         // Sleep until the time for the next frame
         auto currentTime = std::chrono::steady_clock::now();
         auto elapsedTime = std::chrono::duration_cast<std::chrono::milliseconds>(currentTime - lastFrameTime);
-        auto sleepTime = frameDuration - elapsedTime;
+        auto sleepTime = m_frameDuration - elapsedTime;
         bool timeOut = sleepTime <= std::chrono::milliseconds::zero();
 
         if (!timeOut && !m_skipFrame)
@@ -346,6 +346,17 @@ void Engine::run()
     }
 }
 
+double Engine::fps() const
+{
+    return m_fps;
+}
+
+void Engine::setFps(double fps)
+{
+    m_fps = fps;
+    updateFrameDuration();
+}
+
 bool Engine::broadcastRunning(unsigned int index, VirtualMachine *sourceScript)
 {
     const auto &scripts = m_runningBroadcastMap[index];
@@ -757,3 +768,8 @@ BlockSectionContainer *Engine::blockSectionContainer(IBlockSection *section) con
 
     return nullptr;
 }
+
+void Engine::updateFrameDuration()
+{
+    m_frameDuration = std::chrono::milliseconds(static_cast<long>(1000 / m_fps));
+}

src/engine/internal/engine.h

@@ -36,6 +36,9 @@ class Engine : public IEngine
         void initClone(libscratchcpp::Sprite *clone) override;
         void run() override;
 
+        double fps() const override;
+        void setFps(double fps) override;
+
         bool broadcastRunning(unsigned int index, VirtualMachine *sourceScript) override;
 
         void breakFrame() override;
@@ -91,6 +94,8 @@ class Engine : public IEngine
         std::shared_ptr<Entity> getEntity(const std::string &id);
         std::shared_ptr<IBlockSection> blockSection(const std::string &opcode) const;
 
+        void updateFrameDuration();
+
         std::unordered_map<std::shared_ptr<IBlockSection>, std::unique_ptr<BlockSectionContainer>> m_sections;
         std::vector<std::shared_ptr<Target>> m_targets;
         std::vector<std::shared_ptr<Broadcast>> m_broadcasts;
@@ -107,6 +112,8 @@ class Engine : public IEngine
 
         std::unique_ptr<ITimer> m_defaultTimer;
         ITimer *m_timer = nullptr;
+        double m_fps = 30;                         // default FPS
+        std::chrono::milliseconds m_frameDuration; // will be computed in run()
 
         bool m_breakFrame = false;
         bool m_skipFrame = false;

test/engine/engine_test.cpp

@@ -34,6 +34,15 @@ TEST(EngineTest, Clear)
     ASSERT_TRUE(engine.registeredSections().empty());
 }
 
+TEST(EngineTest, Fps)
+{
+    Engine engine;
+    ASSERT_EQ(engine.fps(), 30);
+
+    engine.setFps(60.25);
+    ASSERT_EQ(engine.fps(), 60.25);
+}
+
 TEST(EngineTest, BreakFrame)
 {
     Engine engine;

test/mocks/enginemock.h

@@ -24,6 +24,9 @@ class EngineMock : public IEngine
         MOCK_METHOD(void, initClone, (Sprite *), (override));
         MOCK_METHOD(void, run, (), (override));
 
+        MOCK_METHOD(double, fps, (), (const, override));
+        MOCK_METHOD(void, setFps, (double fps), (override));
+
         MOCK_METHOD(bool, broadcastRunning, (unsigned int, VirtualMachine *), (override));
 
         MOCK_METHOD(void, breakFrame, (), (override));