glsl: Document lower_packed_varyings' "flat" requirement with an assert.

To minimize the variety of type conversions that lower_packed_varyings
needs to perform, it assumes that integral varyings are always
qualified as "flat".  link_varyings.cpp takes care of ensuring that
this is the case (even in the circumstances where GLSL doesn't require
it).

This patch documents the assumption with an assertion, for ease in
future debugging.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

diff --git a/src/glsl/lower_packed_varyings.cpp b/src/glsl/lower_packed_varyings.cpp
index b4cc5cd0d529b6a0ebd0863526e43885bc4fcd07..cdf2289b4e2141c20bea61ba673a3ec4cbc90d3c 100644 (file)
--- a/src/glsl/lower_packed_varyings.cpp
+++ b/src/glsl/lower_packed_varyings.cpp
@@ -178,6 +178,14 @@ lower_packed_varyings_visitor::run(exec_list *instructions)
           !this->needs_lowering(var))
          continue;
 
+      /* This lowering pass is only capable of packing floats and ints
+       * together when their interpolation mode is "flat".  Therefore, to be
+       * safe, caller should ensure that integral varyings always use flat
+       * interpolation, even when this is not required by GLSL.
+       */
+      assert(var->interpolation == INTERP_QUALIFIER_FLAT ||
+             !var->type->contains_integer());
+
       /* Change the old varying into an ordinary global. */
       var->mode = ir_var_auto;