glx: Allow a context-specific fallback for glXGetProcAddress

In applegl, GLX advertises the same extensions provided by OpenGL.framework
even if such extensions are not provided by glapi.  This allows a client
to get access to such API.

Signed-off-by: Jeremy Huddleston <jeremyhu@apple.com>

src/glx/applegl_glx.c

@@ -34,10 +34,12 @@
 #if defined(GLX_USE_APPLEGL)
 
 #include <stdbool.h>
+#include <dlfcn.h>
 
 #include "glxclient.h"
 #include "apple_glx_context.h"
 #include "apple_glx.h"
+#include "apple_cgl.h"
 #include "glx_error.h"
 
 static void
@@ -82,6 +84,12 @@ applegl_wait_x(struct glx_context *gc)
    apple_glx_waitx(dpy, gc->driContext);
 }
 
+static void *
+applegl_get_proc_address(const char *symbol)
+{
+   return dlsym(apple_cgl_get_dl_handle(), symbol);
+}
+
 static const struct glx_context_vtable applegl_context_vtable = {
    applegl_destroy_context,
    applegl_bind_context,
@@ -91,6 +99,7 @@ static const struct glx_context_vtable applegl_context_vtable = {
    DRI_glXUseXFont,
    NULL, /* bind_tex_image, */
    NULL, /* release_tex_image, */
+   applegl_get_proc_address,
 };
 
 struct glx_context *

src/glx/dri2_glx.c

@@ -767,6 +767,7 @@ static const struct glx_context_vtable dri2_context_vtable = {
    DRI_glXUseXFont,
    dri2_bind_tex_image,
    dri2_release_tex_image,
+   NULL, /* get_proc_address */
 };
 
 static void

src/glx/dri_glx.c

@@ -558,6 +558,7 @@ static const struct glx_context_vtable dri_context_vtable = {
    DRI_glXUseXFont,
    NULL,
    NULL,
+   NULL, /* get_proc_address */
 };
 
 static struct glx_context *

src/glx/drisw_glx.c

@@ -296,6 +296,7 @@ static const struct glx_context_vtable drisw_context_vtable = {
    DRI_glXUseXFont,
    NULL,
    NULL,
+   NULL, /* get_proc_address */
 };
 
 static struct glx_context *

src/glx/glxclient.h

@@ -224,7 +224,7 @@ struct glx_context_vtable {
 			  GLXDrawable drawable,
 			  int buffer, const int *attrib_list);
    void (*release_tex_image)(Display * dpy, GLXDrawable drawable, int buffer);
-   
+   void * (*get_proc_address)(const char *symbol);
 };
 
 extern void

src/glx/glxcmds.c

@@ -2521,6 +2521,12 @@ _X_EXPORT void (*glXGetProcAddressARB(const GLubyte * procName)) (void)
 #endif
       if (!f)
          f = (gl_function) _glapi_get_proc_address((const char *) procName);
+      if (!f) {
+         struct glx_context *gc = __glXGetCurrentContext();
+      
+         if (gc != NULL && gc->vtable->get_proc_address != NULL)
+            f = gc->vtable->get_proc_address((const char *) procName);
+      }
    }
    return f;
 }

src/glx/indirect_glx.c

@@ -335,6 +335,7 @@ static const struct glx_context_vtable indirect_context_vtable = {
    indirect_use_x_font,
    indirect_bind_tex_image,
    indirect_release_tex_image,
+   NULL, /* get_proc_address */
 };
 
 /**