Implement new screen extension API.

This new API lets the loader examine DRI level extensions provided by the
driver in a forward compatible manner.

Much of the churn in the DRI interface is adding support for new
extensions or removing old, unused extensions.  This new extension
mechanism lets the loader query the extensions provided by the driver
and implement the extensions it knows about.  Deprecating extensions
is done by not exporting that extension in the list, which doesn't
require keeping old function pointers around to preserve ABI.

include/GL/internal/dri_interface.h

@@ -56,9 +56,24 @@ typedef struct __DRIdriverRec		__DRIdriver;
 typedef struct __DRIframebufferRec	__DRIframebuffer;
 typedef struct __DRIversionRec		__DRIversion;
 typedef struct __DRIinterfaceMethodsRec	__DRIinterfaceMethods;
+
+typedef struct __DRIextensionRec	__DRIextension;
 /*@}*/
 
 
+/**
+ * Extension struct.  Drivers 'inherit' from this struct by embedding
+ * it as the first element in the extension struct.  The
+ * __DRIscreen::getExtensions entry point will return a list of these
+ * structs and the loader can use the extensions it knows about by
+ * casting it to a more specific extension and optionally advertising
+ * the GLX extension.  See below for examples.
+ */
+struct __DRIextensionRec {
+    const char *name;
+};
+
+
 /**
  * \name Functions provided by the driver loader.
  */
@@ -274,6 +289,11 @@ struct __DRIscreenRec {
      */
     void (*destroyScreen)(__DRIscreen *screen);
 
+    /**
+     * Method to get screen extensions.
+     */
+    const __DRIextension **(*getExtensions)(__DRIscreen *screen);
+
     /**
      * Method to create the private DRI drawable data and initialize the
      * drawable dependent methods.

src/glx/x11/glxext.c

@@ -1011,6 +1011,18 @@ CallCreateNewScreen(Display *dpy, int scrn, __GLXscreenConfigs *psc,
 
     return psp;
 }
+
+static void queryExtensions(__GLXscreenConfigs *psc)
+{
+    const __DRIextension **extensions;
+    int i;
+
+    extensions = psc->driScreen.getExtensions(&psc->driScreen);
+    for (i = 0; extensions[i]; i++) {
+	/* Unknown extension, just ignore... */
+    }
+}
+
 #endif /* GLX_DIRECT_RENDERING */
 
 
@@ -1205,6 +1217,8 @@ static Bool AllocAndFetchScreenConfigs(Display *dpy, __GLXdisplayPrivate *priv)
 		    CallCreateNewScreen(dpy, i, psc,
 					& priv->driDisplay,
 					priv->driDisplay.createNewScreen[i] );
+		if (psc->driScreen.private != NULL)
+		    queryExtensions(psc);
 	    }
 	}
 #endif

src/mesa/drivers/dri/common/dri_util.c

@@ -624,6 +624,14 @@ driCreateNewContext(__DRIscreen *screen, const __GLcontextModes *modes,
 }
 /*@}*/
 
+static const __DRIextension **
+driGetExtensions(__DRIscreen *screen)
+{
+    __DRIscreenPrivate *psp = screen->private;
+    static const __DRIextension *extensions[1];
+
+    return extensions;
+}
 
 /*****************************************************************/
 /** \name Screen handling functions                              */
@@ -750,6 +758,7 @@ void * __DRI_CREATE_NEW_SCREEN( int scrn, __DRIscreen *psc,
     psp->dummyContextPriv.driScreenPriv = NULL;
 
     psc->destroyScreen     = driDestroyScreen;
+    psc->getExtensions     = driGetExtensions;
     psc->createNewDrawable = driCreateNewDrawable;
     psc->getMSC            = driGetMSC;
     psc->createNewContext  = driCreateNewContext;