Relax native access header constraints

README.md

@@ -72,6 +72,7 @@ used by the tests and examples and are not required to build the library.
  - Added `GLFW_CONTEXT_NO_ERROR` context hint for `GL_KHR_no_error` support
  - Added `GLFW_TRUE` and `GLFW_FALSE` as client API independent boolean values
  - Added `glfwGetGLXWindow` to query the `GLXWindow` of a window
+ - Relaxed rules for native access header macros
  - Removed dependency on external OpenGL or OpenGL ES headers
  - [Win32] Added support for Windows 8.1 per-monitor DPI
  - [Cocoa] Removed support for OS X 10.6

include/GLFW/glfw3native.h

@@ -50,9 +50,8 @@ extern "C" {
  *  doing and how to fix problems caused by using them.  If you don't, you
  *  shouldn't be using them.**
  *
- *  Before the inclusion of @ref glfw3native.h, you must define exactly one
- *  window system API macro and exactly one context creation API macro.  Failure
- *  to do this will cause a compile-time error.
+ *  Before the inclusion of @ref glfw3native.h, you may define exactly one
+ *  window system API macro and zero or more context creation API macros.
  *
  *  The chosen backends must match those the library was compiled for.  Failure
  *  to do this will cause a link-time error.
@@ -101,20 +100,19 @@ extern "C" {
  #include <wayland-client.h>
 #elif defined(GLFW_EXPOSE_NATIVE_MIR)
  #include <mir_toolkit/mir_client_library.h>
-#else
- #error "No window API selected"
 #endif
 
 #if defined(GLFW_EXPOSE_NATIVE_WGL)
  /* WGL is declared by windows.h */
-#elif defined(GLFW_EXPOSE_NATIVE_NSGL)
+#endif
+#if defined(GLFW_EXPOSE_NATIVE_NSGL)
  /* NSGL is declared by Cocoa.h */
-#elif defined(GLFW_EXPOSE_NATIVE_GLX)
+#endif
+#if defined(GLFW_EXPOSE_NATIVE_GLX)
  #include <GL/glx.h>
-#elif defined(GLFW_EXPOSE_NATIVE_EGL)
+#endif
+#if defined(GLFW_EXPOSE_NATIVE_EGL)
  #include <EGL/egl.h>
-#else
- #error "No context API selected"
 #endif