resolver lifecycle fix

Author: mbaetgen-wup

src/api/include/projectM-4/core.h

@@ -38,8 +38,10 @@ extern "C" {
  * If this function returns NULL, in most cases the OpenGL context is not initialized, not made
  * current or insufficient to render projectM visuals.
  *
- * Note: The OpenGL resolver is initialized on the first invocation of either projectm_create() or projectm_create_with_opengl_load_proc().
- *       All projectM instances created will use the same resolver.
+ * Note: The OpenGL resolver is initialized on the first call to either projectm_create() or projectm_create_with_opengl_load_proc().
+ * All projectM instances share the same resolver, and subsequent calls ignore the provided load_proc.
+ * The resolver instance is tied to the lifecycle of the created projectM instances.
+ * It is released when the last projectM instance is released, and can be reinitialized.
  *
  * @return A projectM handle for the newly created instance that must be used in subsequent API calls.
  *         NULL if the instance could not be created successfully.
@@ -54,8 +56,10 @@ PROJECTM_EXPORT projectm_handle projectm_create();
  * If this function returns NULL, in most cases the OpenGL context is not initialized, not made
  * current or insufficient to render projectM visuals.
  *
- * Note: The OpenGL resolver is initialized on the first invocation of either projectm_create() or projectm_create_with_opengl_load_proc().
- *       All projectM instances created will use the same resolver and subsequent calls will ignore the given load_proc.
+ * Note: The OpenGL resolver is initialized on the first call to either projectm_create() or projectm_create_with_opengl_load_proc().
+ * All projectM instances share the same resolver, and subsequent calls ignore the provided load_proc.
+ * The resolver instance is tied to the lifecycle of the created projectM instances.
+ * It is released when the last projectM instance is released, and can be reinitialized.
  *
  * @return A projectM handle for the newly created instance that must be used in subsequent API calls.
  *         NULL if the instance could not be created successfully.

src/libprojectM/ProjectM.hpp

@@ -296,7 +296,7 @@ class PROJECTM_EXPORT ProjectM
     bool m_presetLocked{false};         //!< If true, the preset change event will not be sent.
     bool m_presetChangeNotified{false}; //!< Stores whether the user has been notified that projectM wants to switch the preset.
 
-    std::shared_ptr<Renderer::Platform::GLResolver> m_glResolver;                 //!< Function resolver for accessing GL backend.
+    std::shared_ptr<Renderer::Platform::GLResolver> m_glResolver;                 //!< Function resolver for accessing GL backend. Stored for keeping ref count, may be null.
     std::unique_ptr<PresetFactoryManager> m_presetFactoryManager; //!< Provides access to all available preset factories.
 
     Audio::PCM m_audioStorage;                                                    //!< Audio data buffer and analyzer instance.

src/libprojectM/Renderer/PlatformGLResolver.cpp

@@ -28,7 +28,16 @@ GLResolver::~GLResolver()
 
 auto GLResolver::Instance() -> std::shared_ptr<GLResolver>
 {
-    static const std::shared_ptr<GLResolver> instance = std::make_shared<GLResolver>();
+    // observe resolver instance with a weak pointer
+    // so that it is shared, but released once the last
+    // client shared_ptr is released
+    static std::weak_ptr<GLResolver> sharedInstance;
+    auto instance = sharedInstance.lock();
+    if (!instance)
+    {
+        instance = std::make_shared<GLResolver>();
+        sharedInstance = instance;
+    }
     return instance;
 }