draw,llvmpipe,util: add depth bias calculation for arb_depth_buffer_float

With this patch, the llvmpipe and draw modules will calculate the depth bias
according to floating point depth buffer semantics described in the
arb_depth_buffer_float specification, when the driver has a z buffer bound
with a format type of UTIL_FORMAT_TYPE_FLOAT.

By default, the driver will use the existing UNORM calculation for depth bias.

A new function, draw_set_zs_format, was added to calculate the Minimum
Resolvable Depth value and floating point depth sense for the draw module.

Reviewed-by: Jose Fonseca <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>

1 files changed, 13 insertions, 5 deletions

diff --git a/src/gallium/auxiliary/draw/draw_context.c b/src/gallium/auxiliary/draw/draw_context.c
index 641dd82ee28..2b3bc0d0ece 100644
--- a/src/gallium/auxiliary/draw/draw_context.c
+++ b/src/gallium/auxiliary/draw/draw_context.c
@@ -38,6 +38,7 @@
 #include "util/u_inlines.h"
 #include "util/u_helpers.h"
 #include "util/u_prim.h"
+#include "util/u_format.h"
 #include "draw_context.h"
 #include "draw_pipe.h"
 #include "draw_prim_assembler.h"
@@ -164,6 +165,8 @@ boolean draw_init(struct draw_context *draw)
    draw->quads_always_flatshade_last = !draw->pipe->screen->get_param(
       draw->pipe->screen, PIPE_CAP_QUADS_FOLLOW_PROVOKING_VERTEX_CONVENTION);
 
+   draw->floating_point_depth = false;
+
    return TRUE;
 }
 
@@ -233,15 +236,20 @@ void draw_flush( struct draw_context *draw )
 
 
 /**
- * Specify the Minimum Resolvable Depth factor for polygon offset.
+ * Specify the depth stencil format for the draw pipeline. This function
+ * determines the Minimum Resolvable Depth factor for polygon offset.
  * This factor potentially depends on the number of Z buffer bits,
  * the rasterization algorithm and the arithmetic performed on Z
- * values between vertex shading and rasterization.  It will vary
- * from one driver to another.
+ * values between vertex shading and rasterization.
  */
-void draw_set_mrd(struct draw_context *draw, double mrd)
+void draw_set_zs_format(struct draw_context *draw, enum pipe_format format)
 {
-   draw->mrd = mrd;
+   const struct util_format_description *desc = util_format_description(format);
+
+   draw->floating_point_depth =
+      (util_get_depth_format_type(desc) == UTIL_FORMAT_TYPE_FLOAT);
+
+   draw->mrd = util_get_depth_format_mrd(desc);
 }