Revert "Refactor DirectX specific code into its own class, like OpenGL"

This reverts commit 5d23755.

Author: ejaquay

BuildConfig.h

@@ -27,21 +27,14 @@
 
 
 //
-// Enable the use of OpenGL display driver
+// Enable the use of OpenGL display driver, otherwise use DirectX.
 //
 #ifndef _LEGACY_VCC
 #ifndef USE_OPENGL
 #define USE_OPENGL true
 #endif
 #endif
 
-//
-// Enable the use of DirectX display driver
-//
-#ifndef USE_DIRECTX
-#define USE_DIRECTX true
-#endif
-
 //
 // Enable black fill to preserve aspect ratio, otherwise replicate border color.
 //
@@ -91,6 +84,13 @@
 // 
 // Edit options above rather than these:
 //
+#if !USE_OPENGL
+#define USE_DIRECTX true
+#endif
+
+#if USE_OPENGL && USE_DIRECTX
+#error Enable either USE_OPENGL or USE_DIRECTX not both.
+#endif
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 // Options that are always off for release