Add step() to IEngine

Author: adazem009

include/scratchcpp/iengine.h

@@ -81,6 +81,9 @@ class LIBSCRATCHCPP_EXPORT IEngine
         /*! Automatically called from clones that are being deleted. */
         virtual void deinitClone(std::shared_ptr<Sprite> clone) = 0;
 
+        /*! Steps all currently running threads. Use this to implement a custom event loop. */
+        virtual void step() = 0;
+
         /*!
          * Calls and runs "when green flag clicked" blocks.
          * \note This function returns when all scripts finish.\n

src/engine/internal/engine.cpp

@@ -261,6 +261,24 @@ void Engine::deinitClone(std::shared_ptr<Sprite> clone)
     m_executableTargets.erase(std::remove(m_executableTargets.begin(), m_executableTargets.end(), clone.get()), m_executableTargets.end());
 }
 
+void Engine::step()
+{
+    // https://github.com/scratchfoundation/scratch-vm/blob/f1aa92fad79af17d9dd1c41eeeadca099339a9f1/src/engine/runtime.js#L2087C6-L2155
+    updateFrameDuration();
+
+    // Clean up threads that were told to stop during or since the last step
+    m_threads.erase(std::remove_if(m_threads.begin(), m_threads.end(), [](std::shared_ptr<VirtualMachine> thread) { return thread->atEnd(); }), m_threads.end());
+
+    m_redrawRequested = false;
+
+    // Step threads
+    stepThreads();
+
+    // Render
+    if (m_redrawHandler)
+        m_redrawHandler();
+}
+
 void Engine::run()
 {
     start();
@@ -285,23 +303,6 @@ void Engine::setRedrawHandler(const std::function<void()> &handler)
     m_redrawHandler = handler;
 }
 
-void Engine::step()
-{
-    // https://github.com/scratchfoundation/scratch-vm/blob/f1aa92fad79af17d9dd1c41eeeadca099339a9f1/src/engine/runtime.js#L2087C6-L2155
-
-    // Clean up threads that were told to stop during or since the last step
-    m_threads.erase(std::remove_if(m_threads.begin(), m_threads.end(), [](std::shared_ptr<VirtualMachine> thread) { return thread->atEnd(); }), m_threads.end());
-
-    m_redrawRequested = false;
-
-    // Step threads
-    stepThreads();
-
-    // Render
-    if (m_redrawHandler)
-        m_redrawHandler();
-}
-
 std::vector<std::shared_ptr<VirtualMachine>> Engine::stepThreads()
 {
     // https://github.com/scratchfoundation/scratch-vm/blob/develop/src/engine/sequencer.js#L70-L173
@@ -372,7 +373,6 @@ void Engine::stepThread(std::shared_ptr<VirtualMachine> thread)
 
 void Engine::eventLoop(bool untilProjectStops)
 {
-    updateFrameDuration();
     m_stopEventLoop = false;
 
     while (true) {

src/engine/internal/engine.h

@@ -42,6 +42,7 @@ class Engine : public IEngine
         void initClone(std::shared_ptr<Sprite> clone) override;
         void deinitClone(std::shared_ptr<Sprite> clone) override;
 
+        void step() override;
         void run() override;
         void runEventLoop() override;
         void stopEventLoop() override;
@@ -156,7 +157,6 @@ class Engine : public IEngine
             KeyOption
         };
 
-        void step();
         std::vector<std::shared_ptr<VirtualMachine>> stepThreads();
         void stepThread(std::shared_ptr<VirtualMachine> thread);
         void eventLoop(bool untilProjectStops = false);
@@ -216,7 +216,7 @@ 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 eventLoop()
+        std::chrono::milliseconds m_frameDuration; // will be computed in step()
         bool m_turboModeEnabled = false;
         std::unordered_map<std::string, bool> m_keyMap; // holds key states
         bool m_anyKeyPressed = false;

test/engine/engine_test.cpp

@@ -70,6 +70,31 @@ TEST(EngineTest, IsRunning)
     ASSERT_FALSE(engine.isRunning());
 }
 
+TEST(EngineTest, Step)
+{
+    Project p("step.sb3");
+    ASSERT_TRUE(p.load());
+
+    p.start();
+
+    auto engine = p.engine();
+    engine->setFps(250);
+    Stage *stage = engine->stage();
+    ASSERT_TRUE(stage);
+
+    ASSERT_VAR(stage, "test1");
+    auto test1 = GET_VAR(stage, "test1");
+
+    ASSERT_VAR(stage, "test2");
+    auto test2 = GET_VAR(stage, "test2");
+
+    for (int i = 1; i <= 3; i++) {
+        engine->step();
+        ASSERT_EQ(test1->value().toInt(), i);
+        ASSERT_EQ(test2->value().toInt(), i > 1 ? 3 : 1);
+    }
+}
+
 TEST(EngineTest, EventLoop)
 {
     Engine engine;

test/mocks/enginemock.h

@@ -25,6 +25,7 @@ class EngineMock : public IEngine
         MOCK_METHOD(void, initClone, (std::shared_ptr<Sprite>), (override));
         MOCK_METHOD(void, deinitClone, (std::shared_ptr<Sprite>), (override));
 
+        MOCK_METHOD(void, step, (), (override));
         MOCK_METHOD(void, run, (), (override));
         MOCK_METHOD(void, runEventLoop, (), (override));
         MOCK_METHOD(void, stopEventLoop, (), (override));