gallium: add a cond rendering hook for vulkan.

The vulkan cond rendering hook is quite different than the
traditional gallium one so add a new interface for it.

This just conditionalises rendering on the memory location.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8182>

docs/gallium/context.rst

@@ -563,6 +563,9 @@ Normally, if the occlusion query returned a non-zero result subsequent
 drawing happens normally so fragments may be generated, shaded and
 processed even where they're known to be obscured.
 
+The ''render_condition_mem'' function specifies the drawing is dependant
+on a value in memory. A buffer resource and offset denote which 32-bit
+value to use for the query. This is used for Vulkan API.
 
 Flushing
 ^^^^^^^^

src/gallium/include/pipe/p_context.h

@@ -153,6 +153,16 @@ struct pipe_context {
                              bool condition,
                              enum pipe_render_cond_flag mode );
 
+   /**
+    * Predicate subsequent rendering on a value in a buffer
+    * \param buffer The buffer to query for the value
+    * \param offset Offset in the buffer to query 32-bit
+    * \param condition whether to skip on FALSE or TRUE query results
+    */
+   void (*render_condition_mem)( struct pipe_context *pipe,
+                                 struct pipe_resource *buffer,
+                                 uint32_t offset,
+                                 bool condition );
    /**
     * Query objects
     */