Pressing 'o' whilst sim is paused, allows the simulation to be stepped.

This does nothing if the simulation isn't ready, e.g. if it hasn't completed a new step since the sim last paused.

Closes #124

src/flamegpu/visualiser/FLAMEGPU_Visualisation.cpp

@@ -68,7 +68,9 @@ bool FLAMEGPU_Visualisation::isReady() const {
 
 
 void FLAMEGPU_Visualisation::lockMutex() {
+    auto lock_t = new std::lock_guard<std::mutex>(vis->getRenderBufferMutexPre());
     lock = new LockHolder(vis->getRenderBufferMutex());
+    delete lock_t;
 }
 void FLAMEGPU_Visualisation::releaseMutex() {
     if (lock) {

src/flamegpu/visualiser/Visualiser.cpp

@@ -902,6 +902,16 @@ void Visualiser::handleKeypress(SDL_Keycode keycode, int /*x*/, int /*y*/) {
             stepsPerSecond = 0.0;
         }
         break;
+    case SDLK_o:
+        // If paused step the simulation, else do nothing
+        if (this->pause_guard) {
+            delete pause_guard;
+            pause_guard = nullptr;
+            const auto pause_guard_t = new std::lock_guard<std::mutex>(render_buffer_mutex_pre);
+            pause_guard = new std::lock_guard<std::mutex>(render_buffer_mutex);
+            delete pause_guard_t;
+        }
+        break;
     case SDLK_l:
         renderLines = !renderLines;
         break;

src/flamegpu/visualiser/Visualiser.h

@@ -241,7 +241,13 @@ class Visualiser : public ViewportExt {
      * This must be locked before calling updateAgentStateBuffer()
      * @see updateAgentStateBuffer(const std::string &, const std::string &, const unsigned int, float *, float *, float *, float *)
      */
-    std::mutex &getRenderBufferMutex() { return render_buffer_mutex; }
+    std::mutex& getRenderBufferMutex() { return render_buffer_mutex; }
+    /**
+     * Returns the mutex for simulation stepping (for the simulation)
+     * This must be locked before locking render_buffer_mutex, then released straight after the lock is achieved
+     * @see updateAgentStateBuffer(const std::string &, const std::string &, const unsigned int, float *, float *, float *, float *)
+     */
+    std::mutex& getRenderBufferMutexPre() { return render_buffer_mutex_pre; }
     /**
      * Sets the value to be rendered to the HUD step counter (if enabled)
      * @param stepCount The step value to be displayed
@@ -381,6 +387,12 @@ class Visualiser : public ViewportExt {
      * Mutex is required to access render buffers for thread safety
      */
     std::mutex render_buffer_mutex;
+    /**
+     * Double mutex to enable simulation stepping
+     * Visualiser must lock this prior to locking render_buffer_mutex, then release this after the render_buffer_mutex lock is achieved
+     * This allows sim stepping to block a re-lock of render_buffer_mutex
+     */
+    std::mutex render_buffer_mutex_pre;
     /**
      * When this is not set to nullptr, it blocks the simulation from continuing
      */