Add glfwGetKeyScancode

Allows retrieval of platform scancode from GLFW_KEY_*.  Implemented for
Win32, Cocoa and X11.  Stubs for Mir and Wayland.

Closes #830.

src/cocoa_window.m

@@ -1511,6 +1511,16 @@ const char* _glfwPlatformGetKeyName(int key, int scancode)
     return _glfw.ns.keyName;
 }
 
+const short int _glfwPlatformGetKeyScancode(int key)
+{
+    if(key <= -1 || key >= (sizeof(_glfw.ns.nativeKeys) / sizeof(_glfw.ns.nativeKeys[0])))
+    {
+        return -1;
+    }
+
+    return _glfw.ns.nativeKeys[key];
+}
+
 int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
                               const GLFWimage* image,
                               int xhot, int yhot)

src/input.c

@@ -256,6 +256,12 @@ GLFWAPI const char* glfwGetKeyName(int key, int scancode)
     return _glfwPlatformGetKeyName(key, scancode);
 }
 
+GLFWAPI const short int glfwGetKeyScancode(int key)
+{
+    _GLFW_REQUIRE_INIT_OR_RETURN(-1);
+    return _glfwPlatformGetKeyScancode(key);
+}
+
 GLFWAPI int glfwGetKey(GLFWwindow* handle, int key)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;

src/internal.h

@@ -542,6 +542,11 @@ void _glfwPlatformSetCursorMode(_GLFWwindow* window, int mode);
  */
 const char* _glfwPlatformGetKeyName(int key, int scancode);
 
+/*! @copydoc glfwGetKeyScancode
+ *  @ingroup platform
+ */
+const short int _glfwPlatformGetKeyScancode(int key);
+
 /*! @copydoc glfwGetMonitors
  *  @ingroup platform
  */

src/mir_window.c

@@ -744,6 +744,13 @@ const char* _glfwPlatformGetKeyName(int key, int scancode)
     return NULL;
 }
 
+const int _glfwPlatformGetKeyScancode(int key)
+{
+    _glfwInputError(GLFW_PLATFORM_ERROR,
+                    "Mir: Unsupported function %s", __PRETTY_FUNCTION__);
+    return NULL;
+}
+
 void _glfwPlatformSetClipboardString(_GLFWwindow* window, const char* string)
 {
     _glfwInputError(GLFW_PLATFORM_ERROR,

src/win32_window.c

@@ -1511,6 +1511,16 @@ const char* _glfwPlatformGetKeyName(int key, int scancode)
     return _glfw.win32.keyName;
 }
 
+const short int _glfwPlatformGetKeyScancode(int key)
+{
+    if(key <= -1 || key >= (sizeof(_glfw.win32.nativeKeys) / sizeof(_glfw.win32.nativeKeys[0])))
+    {
+        return -1;
+    }
+
+    return _glfw.win32.nativeKeys[key];
+}
+
 int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
                               const GLFWimage* image,
                               int xhot, int yhot)

src/wl_window.c

@@ -686,6 +686,12 @@ const char* _glfwPlatformGetKeyName(int key, int scancode)
     return NULL;
 }
 
+const int _glfwPlatformGetKeyScancode(int key)
+{
+    // TODO
+	return -1;
+}
+
 int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
                               const GLFWimage* image,
                               int xhot, int yhot)

src/x11_window.c

@@ -2186,6 +2186,16 @@ const char* _glfwPlatformGetKeyName(int key, int scancode)
     return _glfw.x11.keyName;
 }
 
+const short int _glfwPlatformGetKeyScancode(int key)
+{
+    if(key <= -1 || key >= (sizeof(_glfw.x11.nativeKeys) / sizeof(_glfw.x11.nativeKeys[0])))
+    {
+        return -1;
+    }
+
+    return _glfw.x11.nativeKeys[key];
+}
+
 int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
                               const GLFWimage* image,
                               int xhot, int yhot)