i965: Don't try to continue space before the start of a VBO.

This loop is trying to see if all the buffers to be uploaded happen to
be the same increment from the start of the 3DSTATE_VERTEX_BUFFERS
currently loaded in the hardware.  However, we might be at a smaller
offset than the previous set of VERTEX_BUFFERS, so we can't reuse
because that packet made the first entry be its starting offset (you
can't access outside the given bounds).

Fixes piglit ARB_vertex_buffer_object/elements-negative-offset.

diff --git a/src/mesa/drivers/dri/i965/brw_draw_upload.c b/src/mesa/drivers/dri/i965/brw_draw_upload.c
index 13d3aa7..32a1d29 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_draw_upload.c
+++ b/src/mesa/drivers/dri/i965/brw_draw_upload.c
@@ -500,6 +500,8 @@ static void brw_prepare_vertices(struct brw_context *brw)
            break;
 
         d = brw->vb.buffers[i].offset - brw->vb.current_buffers[i].offset;
+        if (d < 0)
+           break;
         if (i == 0)
            delta = d / brw->vb.current_buffers[i].stride;
         if (delta * brw->vb.current_buffers[i].stride != d)