[Mesa-dev] [PATCH] i965/fs: Don't try to use bogus interpolation modes pre-Gen6.

[Chris Forbes]

Interpolation modes other than perspective-barycentric-pixel-center (and
their associated coefficients in the WM payload) only exist in Gen6 and
later.

Unfortunately, if a varying was declared as `centroid`, we would blindly
read the nonexistant values, and so produce all manner of bad behavior
-- texture swimming, snow, etc.

Fixes rendering in Counter-Strike Source and Team Fortress 2 on
Ironlake.

Signed-off-by: Chris Forbes <chrisf at ijw.co.nz>
---
 src/mesa/drivers/dri/i965/brw_fs.cpp | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 66e78d0..1d810d8 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -984,16 +984,24 @@ fs_visitor::emit_linterp(const fs_reg &attr, const fs_reg &interp,
                          bool is_centroid)
 {
    brw_wm_barycentric_interp_mode barycoord_mode;
-   if (is_centroid) {
-      if (interpolation_mode == INTERP_QUALIFIER_SMOOTH)
-         barycoord_mode = BRW_WM_PERSPECTIVE_CENTROID_BARYCENTRIC;
-      else
-         barycoord_mode = BRW_WM_NONPERSPECTIVE_CENTROID_BARYCENTRIC;
+   if (intel->gen >= 6) {
+      if (is_centroid) {
+         if (interpolation_mode == INTERP_QUALIFIER_SMOOTH)
+            barycoord_mode = BRW_WM_PERSPECTIVE_CENTROID_BARYCENTRIC;
+         else
+            barycoord_mode = BRW_WM_NONPERSPECTIVE_CENTROID_BARYCENTRIC;
+      } else {
+         if (interpolation_mode == INTERP_QUALIFIER_SMOOTH)
+            barycoord_mode = BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC;
+         else
+            barycoord_mode = BRW_WM_NONPERSPECTIVE_PIXEL_BARYCENTRIC;
+      }
    } else {
-      if (interpolation_mode == INTERP_QUALIFIER_SMOOTH)
-         barycoord_mode = BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC;
-      else
-         barycoord_mode = BRW_WM_NONPERSPECTIVE_PIXEL_BARYCENTRIC;
+      /* On Ironlake and below, there is only one interpolation mode.
+       * Centroid interpolation doesn't mean anything on this hardware --
+       * there is no multisampling.
+       */
+      barycoord_mode = BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC;
    }
    return emit(FS_OPCODE_LINTERP, attr,
                this->delta_x[barycoord_mode],
-- 
1.8.2.1