[#8] add CoreManager-Class and basic glfw-Functions

config/Sources.cmake

@@ -2,4 +2,6 @@
 set(vkcv_sources
 		${vkcv_source}/vkcv/Context.hpp
 		${vkcv_source}/vkcv/Context.cpp
+		${vkcv_source}/vkcv/CoreManager.hpp
+		${vkcv_source}/vkcv/CoreManager.cpp
 )

src/vkcv/CoreManager.cpp

+#define GLFW_INCLUDE_VULKAN
+
+#include "CoreManager.hpp"
+
+namespace vkcv {
+
+    int glfwCounter = 0;
+
+    void initGLFW() {
+
+        if (glfwCounter == 0) {
+            int glfwSuccess = glfwInit();
+
+            if (glfwSuccess == GLFW_FALSE) {
+                throw std::runtime_error("Could not initialize GLFW");
+            }
+        }
+        glfwCounter++;
+    }
+
+    void terminateGLFW() {
+        if (glfwCounter == 1) {
+            glfwTerminate();
+        }
+        glfwCounter--;
+    }
+}
\ No newline at end of file

src/vkcv/CoreManager.hpp

+#ifndef VKCV_COREMANAGER_HPP
+#define VKCV_COREMANAGER_HPP
+
+#include <GLFW/glfw3.h>
+#include <stdexcept>
+
+namespace vkcv {
+
+    /**
+     * initialize GLFW if not initialized
+     */
+    void initGLFW();
+    /**
+     * terminate GLFW
+     */
+    void terminateGLFW();
+}
+
+#endif //VKCV_COREMANAGER_HPP