gallium: added draw_set_mrd() function to fix polygon offset

The Minimum Resolvable Depth factor depends on the driver and can't just
be computed from the number of Z buffer bits.
Glean's polygon offset test now passes with softpipe.
Still need to determine the MRD factor for other gallium drivers, if they use
the draw module's polygon offset stage...

1 files changed, 20 insertions, 0 deletions

diff --git a/src/gallium/drivers/softpipe/sp_state_surface.c b/src/gallium/drivers/softpipe/sp_state_surface.c
index ba8c9eece7..8877b18af9 100644
--- a/src/gallium/drivers/softpipe/sp_state_surface.c
+++ b/src/gallium/drivers/softpipe/sp_state_surface.c
@@ -101,6 +101,26 @@ softpipe_set_framebuffer_state(struct pipe_context *pipe,
    }
 #endif
 
+   /* Tell draw module how deep the Z/depth buffer is */
+   {
+      int depth_bits;
+      double mrd;
+      if (sp->framebuffer.zsbuf) {
+         depth_bits = pf_get_component_bits(sp->framebuffer.zsbuf->format,
+                                            PIPE_FORMAT_COMP_Z);
+      }
+      else {
+         depth_bits = 0;
+      }
+      if (depth_bits > 16) {
+         mrd = 0.0000001;
+      }
+      else {
+         mrd = 0.00002;
+      }
+      draw_set_mrd(sp->draw, mrd);
+   }
+
    sp->framebuffer.width = fb->width;
    sp->framebuffer.height = fb->height;