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]>

3 files changed, 36 insertions, 11 deletions

diff --git a/src/gallium/auxiliary/util/u_format.c b/src/gallium/auxiliary/util/u_format.c
index 9ef3bb53ff2..6b602bf3262 100644
--- a/src/gallium/auxiliary/util/u_format.c
+++ b/src/gallium/auxiliary/util/u_format.c
@@ -215,9 +215,8 @@ util_format_is_supported(enum pipe_format format, unsigned bind)
  * default MRD will be 1.0 / ((1 << 24) - 1).
  */
 double
-util_get_depth_format_mrd(enum pipe_format format)
+util_get_depth_format_mrd(const struct util_format_description *desc)
 {
-   struct util_format_description *format_desc;
    /*
     * Depth buffer formats without a depth component OR scenarios
     * without a bound depth buffer default to D24.
@@ -225,23 +224,20 @@ util_get_depth_format_mrd(enum pipe_format format)
    double mrd = 1.0 / ((1 << 24) - 1);
    unsigned depth_channel;
 
-   format_desc = (struct util_format_description *)
-                     util_format_description(format);
-
-   assert(format_desc);
+   assert(desc);
 
    /*
     * Some depth formats do not store the depth component in the first
     * channel, detect the format and adjust the depth channel. Get the
     * swizzled depth component channel.
     */
-   depth_channel = format_desc->swizzle[0];
+   depth_channel = desc->swizzle[0];
 
-   if (format_desc->channel[depth_channel].type == UTIL_FORMAT_TYPE_UNSIGNED &&
-       format_desc->channel[depth_channel].normalized) {
+   if (desc->channel[depth_channel].type == UTIL_FORMAT_TYPE_UNSIGNED &&
+       desc->channel[depth_channel].normalized) {
       int depth_bits;
 
-      depth_bits = format_desc->channel[depth_channel].size;
+      depth_bits = desc->channel[depth_channel].size;
       mrd = 1.0 / ((1ULL << depth_bits) - 1);
    }
 
diff --git a/src/gallium/auxiliary/util/u_format.h b/src/gallium/auxiliary/util/u_format.h
index 369c3994ad3..0fbaf4cc154 100644
--- a/src/gallium/auxiliary/util/u_format.h
+++ b/src/gallium/auxiliary/util/u_format.h
@@ -546,13 +546,29 @@ util_format_is_depth_and_stencil(enum pipe_format format)
 
 
 /**
+ * Calculates the depth format type based upon the incoming format description.
+ */
+static INLINE unsigned
+util_get_depth_format_type(const struct util_format_description *desc)
+{
+   unsigned depth_channel = desc->swizzle[0];
+   if (desc->colorspace == UTIL_FORMAT_COLORSPACE_ZS &&
+       depth_channel != UTIL_FORMAT_SWIZZLE_NONE) {
+      return desc->channel[depth_channel].type;
+   } else {
+      return UTIL_FORMAT_TYPE_VOID;
+   }
+}
+
+
+/**
  * Calculates the MRD for the depth format. MRD is used in depth bias
  * for UNORM and unbound depth buffers. When the depth buffer is floating
  * point, the depth bias calculation does not use the MRD. However, the
  * default MRD will be 1.0 / ((1 << 24) - 1).
  */
 double
-util_get_depth_format_mrd(enum pipe_format format);
+util_get_depth_format_mrd(const struct util_format_description *desc);
 
 
 /**
diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
index f5c14ef8d56..426d5daa78c 100644
--- a/src/gallium/auxiliary/util/u_math.h
+++ b/src/gallium/auxiliary/util/u_math.h
@@ -246,6 +246,19 @@ union di {
 
 
 /**
+ * Extract the IEEE float32 exponent.
+ */
+static INLINE signed
+util_get_float32_exponent(float x) {
+   union fi f;
+
+   f.f = x;
+
+   return ((f.ui >> 23) & 0xff) - 127;
+}
+
+
+/**
  * Fast version of 2^x
  * Identity: exp2(a + b) = exp2(a) * exp2(b)
  * Let ipart = int(x)