Mesa (7.10): i965/fs: Fix linear gl_Color interpolation on pre-gen6 hardware.

[Kenneth Graunke]

Module: Mesa
Branch: 7.10
Commit: 73f7453318633f2c5685c10f7bebce91e6e1868f
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=73f7453318633f2c5685c10f7bebce91e6e1868f

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Sat Mar 26 22:04:23 2011 -0700

i965/fs: Fix linear gl_Color interpolation on pre-gen6 hardware.

Civilization 4's shaders make heavy use of gl_Color and don't use
perspective interpolation.  This resulted in rivers, units, trees, and
so on being rendered almost entirely white.  This is a regression
compared to the old fragment shader backend.

Found by inspection (comparing the old and new FS backend code).

References: https://bugs.freedesktop.org/show_bug.cgi?id=32949

(cherry-picked from commit 0c8beb0ab5e72a9d2ecaad51db16a7d5291e120b)

---

 src/mesa/drivers/dri/i965/brw_fs.cpp |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 12ac7a4..524dfaa 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -532,8 +532,10 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
 	    continue;
 	 }
 
-	 if (c->key.flat_shade && (location == FRAG_ATTRIB_COL0 ||
-				   location == FRAG_ATTRIB_COL1)) {
+	 bool is_gl_Color =
+	    location == FRAG_ATTRIB_COL0 || location == FRAG_ATTRIB_COL1;
+
+	 if (c->key.flat_shade && is_gl_Color) {
 	    /* Constant interpolation (flat shading) case. The SF has
 	     * handed us defined values in only the constant offset
 	     * field of the setup reg.
@@ -556,7 +558,7 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
 	       attr.reg_offset++;
 	    }
 
-	    if (intel->gen < 6) {
+	    if (intel->gen < 6 && !(is_gl_Color && c->key.linear_color)) {
 	       attr.reg_offset -= type->vector_elements;
 	       for (unsigned int c = 0; c < type->vector_elements; c++) {
 		  emit(fs_inst(BRW_OPCODE_MUL,