i965: Add helper for lossless compression support

v2: Check explicitly against base type of GL_FLOAT instead of
    using _mesa_is_format_integer_color(). Otherwise we miss
    GL_UNSIGNED_NORMALIZED.
v3 (Ben): Also call intel_miptree_supports_non_msrt_fast_clear()
          in order to really check everything.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>

src/mesa/drivers/dri/i965/intel_mipmap_tree.c

@@ -294,6 +294,32 @@ intel_miptree_is_lossless_compressed(const struct brw_context *brw,
    return mt->num_samples <= 1;
 }
 
+bool
+intel_miptree_supports_lossless_compressed(struct brw_context *brw,
+                                           const struct intel_mipmap_tree *mt)
+{
+   /* For now compression is only enabled for integer formats even though
+    * there exist supported floating point formats also. This is a heuristic
+    * decision based on current public benchmarks. In none of the cases these
+    * formats provided any improvement but a few cases were seen to regress.
+    * Hence these are left to to be enabled in the future when they are known
+    * to improve things.
+    */
+   if (_mesa_get_format_datatype(mt->format) == GL_FLOAT)
+      return false;
+
+   /* Fast clear mechanism and lossless compression go hand in hand. */
+   if (!intel_miptree_supports_non_msrt_fast_clear(brw, mt))
+      return false;
+
+   /* Fast clear can be also used to clear srgb surfaces by using equivalent
+    * linear format. This trick, however, can't be extended to be used with
+    * lossless compression and therefore a check is needed to see if the format
+    * really is linear.
+    */
+   return _mesa_get_srgb_format_linear(mt->format) == mt->format;
+}
+
 /**
  * Determine depth format corresponding to a depth+stencil format,
  * for separate stencil.

src/mesa/drivers/dri/i965/intel_mipmap_tree.h

@@ -678,6 +678,10 @@ bool
 intel_miptree_supports_non_msrt_fast_clear(struct brw_context *brw,
                                            const struct intel_mipmap_tree *mt);
 
+bool
+intel_miptree_supports_lossless_compressed(struct brw_context *brw,
+                                           const struct intel_mipmap_tree *mt);
+
 bool
 intel_miptree_alloc_non_msrt_mcs(struct brw_context *brw,
                                  struct intel_mipmap_tree *mt);