u_draw: Add helper to emultate multi-draw

No need to duplicate this in every driver.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9581>

src/gallium/auxiliary/util/u_draw.c

@@ -191,3 +191,24 @@ util_draw_indirect(struct pipe_context *pipe,
    }
    pipe_buffer_unmap(pipe, transfer);
 }
+
+void
+util_draw_multi(struct pipe_context *pctx, const struct pipe_draw_info *info,
+                const struct pipe_draw_indirect_info *indirect,
+                const struct pipe_draw_start_count *draws,
+                unsigned num_draws)
+{
+   struct pipe_draw_info tmp_info = *info;
+
+   /* If you call this with num_draws==1, that is probably going to be
+    * an infinite loop
+    */
+   assert(num_draws > 1);
+
+   for (unsigned i = 0; i < num_draws; i++) {
+      if (indirect || (draws[i].count && info->instance_count))
+         pctx->draw_vbo(pctx, &tmp_info, indirect, &draws[i], 1);
+      if (tmp_info.increment_draw_id)
+         tmp_info.drawid++;
+   }
+}

src/gallium/auxiliary/util/u_draw.h

@@ -155,6 +155,14 @@ util_draw_indirect(struct pipe_context *pipe,
                    const struct pipe_draw_info *info,
                    const struct pipe_draw_indirect_info *indirect);
 
+/* Helper to handle multi-draw by splitting into individual draws.  You
+ * don't want to call this if num_draws==1
+ */
+void
+util_draw_multi(struct pipe_context *pctx, const struct pipe_draw_info *info,
+                const struct pipe_draw_indirect_info *indirect,
+                const struct pipe_draw_start_count *draws,
+                unsigned num_draws);
 
 unsigned
 util_draw_max_index(