Adds GetCurrentFrameBuffertSize to allow client code to determine the current rendering size.

src/core.c

@@ -1429,6 +1429,12 @@ int GetScreenHeight(void)
     return CORE.Window.screen.height;
 }
 
+// Get width and height of the current rendering context (screen or texture)
+Vector2 GetCurrentFrameBuffertSize()
+{
+    return (Vector2) { (float)CORE.Window.currentFbo.width, (float)CORE.Window.currentFbo.height };
+}
+
 // Get native window handle
 void *GetWindowHandle(void)
 {

src/raylib.h

@@ -918,6 +918,7 @@ RLAPI void SetWindowSize(int width, int height);                  // Set window
 RLAPI void *GetWindowHandle(void);                                // Get native window handle
 RLAPI int GetScreenWidth(void);                                   // Get current screen width
 RLAPI int GetScreenHeight(void);                                  // Get current screen height
+RLAPI Vector2 GetCurrentFrameBuffertSize();                       // Get width and height of the current rendering context (screen or texture)
 RLAPI int GetMonitorCount(void);                                  // Get number of connected monitors
 RLAPI int GetCurrentMonitor(void);                                // Get current connected monitor
 RLAPI Vector2 GetMonitorPosition(int monitor);                    // Get specified monitor position