util: treat denorm'ed floats like zero

The D3D10 spec is very explicit about treatment of denorm floats and
the behavior is exactly the same for them as it would be for -0 or
+0. This makes our shading code match that behavior, since OpenGL
doesn't care and on a few cpu's it's faster (worst case the same).
Float16 conversions will likely break but we'll fix them in a follow
up commit.

Signed-off-by: Zack Rusin <[email protected]>
Reviewed-by: Jose Fonseca <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/draw/draw_pt.c b/src/gallium/auxiliary/draw/draw_pt.c
index d2fe0025bfc..ccde371ffcd 100644
--- a/src/gallium/auxiliary/draw/draw_pt.c
+++ b/src/gallium/auxiliary/draw/draw_pt.c
@@ -459,8 +459,14 @@ draw_vbo(struct draw_context *draw,
    unsigned instance;
    unsigned index_limit;
    unsigned count;
+   unsigned fpstate = util_fpstate_get();
    struct pipe_draw_info resolved_info;
 
+   /* Make sure that denorms are treated like zeros. This is 
+    * the behavior required by D3D10. OpenGL doesn't care.
+    */
+   util_fpstate_set_denorms_to_zero(fpstate);
+
    resolve_draw_info(info, &resolved_info);
    info = &resolved_info;
 
@@ -518,6 +524,7 @@ draw_vbo(struct draw_context *draw,
       if (index_limit == 0) {
       /* one of the buffers is too small to do any valid drawing */
          debug_warning("draw: VBO too small to draw anything\n");
+         util_fpstate_set(fpstate);
          return;
       }
    }
@@ -558,4 +565,5 @@ draw_vbo(struct draw_context *draw,
    if (draw->collect_statistics) {
       draw->render->pipeline_statistics(draw->render, &draw->statistics);
    }
+   util_fpstate_set(fpstate);
 }