Add common header

We're going to use this header to provide shared macros. Right now, we
can use it to replace the:

    #ifdef __cplusplus
    extern "C" {
    #endif

    …

    #ifdef __cplusplus
    }
    #endif

Stanzas for every installed header, with easier to read macros in the
same spirit of Cairo and GLib.

include/epoxy/Makefile.am

@@ -22,6 +22,7 @@
 epoxyincludedir = $(includedir)/epoxy
 
 epoxyinclude_HEADERS = \
+	common.h \
 	gl.h \
         $(EGL_INCLUDES) \
         $(GLX_INCLUDES) \

include/epoxy/common.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2017  Emmanuele Bassi 
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/** @file common.h
+ *
+ * A common header file, used to define macros and shared symbols.
+ */
+
+#ifndef EPOXY_COMMON_H
+#define EPOXY_COMMON_H
+
+#ifdef __cplusplus
+# define EPOXY_BEGIN_DECLS      extern "C" {
+# define EPOXY_END_DECLS        }
+#else
+# define EPOXY_BEGIN_DECLS
+# define EPOXY_END_DECLS
+#endif
+
+#endif /* EPOXY_COMMON_H */

include/epoxy/egl.h

@@ -30,12 +30,10 @@
 #ifndef EPOXY_EGL_H
 #define EPOXY_EGL_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdbool.h>
 
+#include "epoxy/common.h"
+
 #if defined(__egl_h_) || defined(__eglext_h_)
 #error epoxy/egl.h must be included before (or in place of) GL/egl.h
 #else
@@ -45,11 +43,11 @@ extern "C" {
 
 #include "epoxy/egl_generated.h"
 
+EPOXY_BEGIN_DECLS
+
 bool epoxy_has_egl_extension(EGLDisplay dpy, const char *extension);
 int epoxy_egl_version(EGLDisplay dpy);
 
-#ifdef __cplusplus
-} /* extern "C" */
-#endif
+EPOXY_END_DECLS
 
 #endif /* EPOXY_EGL_H */

include/epoxy/gl.h

@@ -30,12 +30,10 @@
 #ifndef EPOXY_GL_H
 #define EPOXY_GL_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdbool.h>
 
+#include "epoxy/common.h"
+
 #if defined(__gl_h_) || defined(__glext_h_)
 #error epoxy/gl.h must be included before (or in place of) GL/gl.h
 #else
@@ -93,12 +91,12 @@ extern "C" {
 
 #include "epoxy/gl_generated.h"
 
+EPOXY_BEGIN_DECLS
+
 EPOXY_IMPORTEXPORT bool epoxy_has_gl_extension(const char *extension);
 EPOXY_IMPORTEXPORT bool epoxy_is_desktop_gl(void);
 EPOXY_IMPORTEXPORT int epoxy_gl_version(void);
 
-#ifdef __cplusplus
-} /* extern "C" */
-#endif
+EPOXY_END_DECLS
 
 #endif /* EPOXY_GL_H */

include/epoxy/glx.h

@@ -30,10 +30,6 @@
 #ifndef EPOXY_GLX_H
 #define EPOXY_GLX_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <epoxy/gl.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
@@ -49,11 +45,11 @@ extern "C" {
 
 #include "epoxy/glx_generated.h"
 
+EPOXY_BEGIN_DECLS
+
 bool epoxy_has_glx_extension(Display *dpy, int screen, const char *extension);
 int epoxy_glx_version(Display *dpy, int screen);
 
-#ifdef __cplusplus
-} /* extern "C" */
-#endif
+EPOXY_END_DECLS
 
 #endif /* EPOXY_GLX_H */

include/epoxy/meson.build

@@ -1,3 +1,5 @@
+headers = [ 'common.h' ]
+
 gl_generated = custom_target('gl_generated.h',
                              input: gl_registry,
                              output: [
@@ -15,7 +17,7 @@ gl_generated = custom_target('gl_generated.h',
                              install_dir: join_paths(epoxy_includedir, 'epoxy'))
 
 gen_headers = [ gl_generated ]
-headers = [ 'gl.h', ]
+headers += [ 'gl.h', ]
 
 if build_egl
   egl_generated = custom_target('egl_generated.h',

include/epoxy/wgl.h

@@ -30,13 +30,11 @@
 #ifndef EPOXY_WGL_H
 #define EPOXY_WGL_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdbool.h>
 #include <windows.h>
 
+#include "epoxy/common.h"
+
 #undef wglUseFontBitmaps
 #undef wglUseFontOutlines
 
@@ -54,11 +52,11 @@ extern "C" {
 
 #include "epoxy/wgl_generated.h"
 
+EPOXY_BEGIN_DECLS
+
 EPOXY_IMPORTEXPORT bool epoxy_has_wgl_extension(HDC hdc, const char *extension);
 EPOXY_IMPORTEXPORT void epoxy_handle_external_wglMakeCurrent(void);
 
-#ifdef __cplusplus
-} /* extern "C" */
-#endif
+EPOXY_END_DECLS
 
 #endif /* EPOXY_WGL_H */