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, 0 deletions

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)