3 files changed, 40 insertions, 0 deletions

diff --git a/src/mesa/vbo/vbo_save.h b/src/mesa/vbo/vbo_save.h
index 9d13e0aa18d..274d667be78 100644
--- a/src/mesa/vbo/vbo_save.h
+++ b/src/mesa/vbo/vbo_save.h
@@ -86,6 +86,20 @@ struct vbo_save_vertex_list {
    struct vbo_save_primitive_store *prim_store;
 };
 
+
+/**
+ * Is the vertex lists's buffer offset an exact multiple of the
+ * vertex size (in bytes)?  This is used to check for a vertex array /
+ * drawing optimization.
+ */
+static inline bool
+aligned_vertex_buffer_offset(const struct vbo_save_vertex_list *node)
+{
+   unsigned vertex_size = node->vertex_size * sizeof(GLfloat); /* in bytes */
+   return vertex_size != 0 && node->buffer_offset % vertex_size == 0;
+}
+
+
 /* These buffers should be a reasonable size to support upload to
  * hardware.  Current vbo implementation will re-upload on any
  * changes, so don't make too big or apps which dynamically create
diff --git a/src/mesa/vbo/vbo_save_api.c b/src/mesa/vbo/vbo_save_api.c
index 42d883fed4d..1c575448773 100644
--- a/src/mesa/vbo/vbo_save_api.c
+++ b/src/mesa/vbo/vbo_save_api.c
@@ -546,6 +546,20 @@ compile_vertex_list(struct gl_context *ctx)
       save->prim_store = alloc_prim_store();
    }
 
+   /*
+    * If the vertex buffer offset is a multiple of the vertex size,
+    * we can use the _mesa_prim::start value to indicate where the
+    * vertices starts, instead of the buffer offset.  Also see the
+    * bind_vertex_list() function.
+    */
+   if (aligned_vertex_buffer_offset(node)) {
+      const unsigned start_offset =
+         node->buffer_offset / (node->vertex_size * sizeof(GLfloat));
+      for (unsigned i = 0; i < save->prim_count; i++) {
+         save->prims[i].start += start_offset;
+      }
+   }
+
    /* Reset our structures for the next run of vertices:
     */
    reset_counters(ctx);
diff --git a/src/mesa/vbo/vbo_save_draw.c b/src/mesa/vbo/vbo_save_draw.c
index 1694a04a3e1..b63a9a8b869 100644
--- a/src/mesa/vbo/vbo_save_draw.c
+++ b/src/mesa/vbo/vbo_save_draw.c
@@ -146,6 +146,18 @@ bind_vertex_list(struct gl_context *ctx,
    memcpy(node_attrsz, node->attrsz, sizeof(node->attrsz));
    memcpy(node_attrtype, node->attrtype, sizeof(node->attrtype));
 
+   if (aligned_vertex_buffer_offset(node)) {
+      /* The vertex size is an exact multiple of the buffer offset.
+       * This means that we can use zero-based vertex attribute pointers
+       * and specify the start of the primitive with the _mesa_prim::start
+       * field.  This results in issuing several draw calls with identical
+       * vertex attribute information.  This can result in fewer state
+       * changes in drivers.  In particular, the Gallium CSO module will
+       * filter out redundant vertex buffer changes.
+       */
+      buffer_offset = 0;
+   }
+
    /* Install the default (ie Current) attributes first, then overlay
     * all active ones.
     */