i965 Gen4/5: clip: Don't mangle flat varyings

This patch ensures that integers will pass through unscathed.  Doing
(useless) computations on them is risky, especially when their bit
patterns correspond to values like inf or nan.

[V1-2]: Signed-off-by: Olivier Galibert <galibert at pobox.com>
Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

diff --git a/src/mesa/drivers/dri/i965/brw_clip_util.c b/src/mesa/drivers/dri/i965/brw_clip_util.c
index b188bf773840581b48ec7debabb4892a258f59ac..8500b8b6663e11c8a402b5910fe4d30af1418de9 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_clip_util.c
+++ b/src/mesa/drivers/dri/i965/brw_clip_util.c
@@ -269,28 +269,39 @@ void brw_clip_interp_vertex( struct brw_clip_compile *c,
          * header), so interpolate:
          *
          *        New = attr0 + t*attr1 - t*attr0
+          *
+          * Unless the attribute is flat shaded -- in which case just copy
+          * from one of the sources (doesn't matter which; already copied from pv)
          */
-         struct brw_reg tmp = get_tmp(c);
-         struct brw_reg t =
-            c->key.interpolation_mode.mode[slot] == INTERP_QUALIFIER_NOPERSPECTIVE ?
-            t_nopersp : t0;
-
-        brw_MUL(p, 
-                vec4(brw_null_reg()),
-                deref_4f(v1_ptr, delta),
-                t);
-
-        brw_MAC(p, 
-                tmp,         
-                negate(deref_4f(v0_ptr, delta)),
-                t); 
-             
-        brw_ADD(p,
-                deref_4f(dest_ptr, delta), 
-                deref_4f(v0_ptr, delta),
-                tmp);
-
-         release_tmp(c, tmp);
+         GLuint interp = c->key.interpolation_mode.mode[slot];
+
+         if (interp != INTERP_QUALIFIER_FLAT) {
+            struct brw_reg tmp = get_tmp(c);
+            struct brw_reg t =
+               interp == INTERP_QUALIFIER_NOPERSPECTIVE ? t_nopersp : t0;
+
+            brw_MUL(p,
+                  vec4(brw_null_reg()),
+                  deref_4f(v1_ptr, delta),
+                  t);
+
+            brw_MAC(p,
+                  tmp,
+                  negate(deref_4f(v0_ptr, delta)),
+                  t);
+
+            brw_ADD(p,
+                  deref_4f(dest_ptr, delta),
+                  deref_4f(v0_ptr, delta),
+                  tmp);
+
+            release_tmp(c, tmp);
+         }
+         else {
+            brw_MOV(p,
+                  deref_4f(dest_ptr, delta),
+                  deref_4f(v0_ptr, delta));
+         }
       }
    }