Fix fullscreen resolution (#1637)

* Always try to set vsync.
Use the internal monitor function to correctly get the display for windows.

* Modified how fullscreen gets toggled.

- Removed the unsetting and setting of the resize callback function. Instead of that I moved the fullscreen flag setting into a more correct place before setting the fullscreen so that this flag can be used in the callback.
- In the resize callback now window size is only set when it is not fullscreen resulting in preserving the window size.
- When going fullscreen the larges resolution is used so that there are no problems of the type when you minimize the window you cannot use anything else in your desktop because the resolution might be too low. If a low res effect is desired one should use render texture (this is the approach all game engines use).

* Set correct return to window in case of fail to get monitor.

* Set the refresh rate on the mode.

* Made changes based on review from @raysan5

Co-authored-by: Jeffery Myers <JeffM2501@gmail.com>

src/core.c

@@ -1044,31 +1044,31 @@ void ToggleFullscreen(void)
         if (!monitor)
         {
             TRACELOG(LOG_WARNING, "GLFW: Failed to get monitor");
-            glfwSetWindowSizeCallback(CORE.Window.handle, NULL);
-            glfwSetWindowMonitor(CORE.Window.handle, glfwGetPrimaryMonitor(), 0, 0, CORE.Window.screen.width, CORE.Window.screen.height, GLFW_DONT_CARE);
-            glfwSetWindowSizeCallback(CORE.Window.handle, WindowSizeCallback);
+    
+            CORE.Window.fullscreen = false;          // Toggle fullscreen flag
+            CORE.Window.flags &= ~FLAG_FULLSCREEN_MODE;
+            
+            glfwSetWindowMonitor(CORE.Window.handle, NULL, 0, 0, CORE.Window.screen.width, CORE.Window.screen.height, GLFW_DONT_CARE);
             return;
         }
     
-        const GLFWvidmode *mode = glfwGetVideoMode(monitor);
-        glfwSetWindowSizeCallback(CORE.Window.handle, NULL);
+        CORE.Window.fullscreen = true;          // Toggle fullscreen flag
+        CORE.Window.flags |= FLAG_FULLSCREEN_MODE;
+        
         glfwSetWindowMonitor(CORE.Window.handle, monitor, 0, 0, CORE.Window.screen.width, CORE.Window.screen.height, GLFW_DONT_CARE);
-        glfwSetWindowSizeCallback(CORE.Window.handle, WindowSizeCallback);
     }
     else
     {
-        glfwSetWindowSizeCallback(CORE.Window.handle, NULL);
+        CORE.Window.fullscreen = false;          // Toggle fullscreen flag
+        CORE.Window.flags &= ~FLAG_FULLSCREEN_MODE;
+        
         glfwSetWindowMonitor(CORE.Window.handle, NULL, CORE.Window.position.x, CORE.Window.position.y, CORE.Window.screen.width, CORE.Window.screen.height, GLFW_DONT_CARE);
-        glfwSetWindowSizeCallback(CORE.Window.handle, WindowSizeCallback);
     }
 
 	// Try to enable GPU V-Sync, so frames are limited to screen refresh rate (60Hz -> 60 FPS)
     // NOTE: V-Sync can be enabled by graphic driver configuration
     if (CORE.Window.flags & FLAG_VSYNC_HINT) glfwSwapInterval(1);
 
-    CORE.Window.fullscreen = !CORE.Window.fullscreen;          // Toggle fullscreen flag
-    CORE.Window.flags ^= FLAG_FULLSCREEN_MODE;
-
 #endif
 #if defined(PLATFORM_WEB)
     /*
@@ -4619,16 +4619,18 @@ static void ErrorCallback(int error, const char *description)
 static void WindowSizeCallback(GLFWwindow *window, int width, int height)
 {
     SetupViewport(width, height);    // Reset viewport and projection matrix for new size
-
+    CORE.Window.currentFbo.width = width;
+    CORE.Window.currentFbo.height = height;
+    CORE.Window.resizedLastFrame = true;
+    
+    if(IsWindowFullscreen())
+        return;
+    
     // Set current screen size
     CORE.Window.screen.width = width;
     CORE.Window.screen.height = height;
-    CORE.Window.currentFbo.width = width;
-    CORE.Window.currentFbo.height = height;
-
     // NOTE: Postprocessing texture is not scaled to new size
 
-    CORE.Window.resizedLastFrame = true;
 }
 
 // GLFW3 WindowIconify Callback, runs when window is minimized/restored