Allow enabling and disabling GLX support

Currently, GLX support in libepoxy at build time is hard coded, but
various platforms have expressed their preference for having a
configure-time option for it.

For instance:

 - various embedded distributors do not ship with X11, but wish to use
   libraries that depend on libepoxy now that Wayland is available
 - distributors for macOS still wish to retain the ability to ship
   their software with X11 enabled

By default, we want epoxy to build with GLX enabled pretty much
everywhere it makes sense, since it's only a build-time option and it's
not a run-time dependency.

meson.build

@@ -30,26 +30,48 @@ conf.set_quoted('PACKAGE_LOCALEDIR', join_paths(get_option('prefix'), get_option
 conf.set_quoted('PACKAGE_LIBEXECDIR', join_paths(get_option('prefix'), get_option('libexecdir')))
 conf.set('HAVE_KHRPLATFORM_H', cc.has_header('KHR/khrplatform.h', required: false))
 
-if host_system == 'windows'
+# GLX can be used on different platforms, so we expose a
+# configure time switch to enable or disable it; in case
+# the "auto" default value is set, we only enable GLX
+# support on Linux and Unix
+enable_glx = get_option('enable-glx')
+if enable_glx == 'auto'
+  if host_system == 'windows'
+    build_glx = false
+  elif host_system == 'darwin'
+    build_glx = false
+  elif host_system == 'android'
+    build_glx = false
+  else
+    build_glx = true
+  endif
+elif enable_glx == 'yes'
+  build_glx = true
+elif enable_glx == 'no'
   build_glx = false
+endif
+
+# The remaining platform specific API for GL/GLES are enabled
+# depending on the platform we're building for
+if host_system == 'windows'
   build_egl = false
   build_apple = false
   build_wgl = true
   has_znow = true
 elif host_system == 'darwin'
-  build_glx = false
   build_egl = false
   build_apple = true
   build_wgl = false
   has_znow = false
 else
-  build_glx = true
   build_egl = true
   build_apple = false
   build_wgl = false
   has_znow = true
 endif
 
+conf.set10('ENABLE_GLX', build_glx)
+
 # Compiler flags, taken from the Xorg macros
 test_cflags = [
   '-Wpointer-arith',

meson_options.txt

@@ -1,3 +1,8 @@
 option('enable-docs',
        type: 'boolean', value: false,
        description: 'Enable generating the Epoxy API reference (depends on Doxygen)')
+option('enable-glx',
+       type: 'combo',
+       choices: [ 'auto', 'yes', 'no' ],
+       value: 'auto',
+       description: 'Enable GLX support')

src/dispatch_common.h

@@ -23,15 +23,13 @@
 
 #include "config.h"
 
-#include <stdbool.h>
-
 #ifdef _WIN32
 #define PLATFORM_HAS_EGL 0
-#define PLATFORM_HAS_GLX 0
+#define PLATFORM_HAS_GLX ENABLE_GLX
 #define PLATFORM_HAS_WGL 1
 #elif defined(__APPLE__)
 #define PLATFORM_HAS_EGL 0
-#define PLATFORM_HAS_GLX 0
+#define PLATFORM_HAS_GLX ENABLE_GLX
 #define PLATFORM_HAS_WGL 0
 #elif defined(ANDROID)
 #define PLATFORM_HAS_EGL 1
@@ -39,7 +37,7 @@
 #define PLATFORM_HAS_WGL 0
 #else
 #define PLATFORM_HAS_EGL 1
-#define PLATFORM_HAS_GLX 1
+#define PLATFORM_HAS_GLX ENABLE_GLX
 #define PLATFORM_HAS_WGL 0
 #endif
 

test/meson.build

@@ -1,6 +1,6 @@
 has_gles1 = gles1_dep.found()
 has_gles2 = gles2_dep.found()
-build_x11_tests = x11_dep.found()
+build_x11_tests = build_glx and x11_dep.found()
 
 test_cflags = common_cflags + [
   '-D_XOPEN_SOURCE',