i965: Use sample barycentric coordinates with per sample shading

Current implementation of arb_sample_shading doesn't set 'Barycentric
Interpolation Mode' correctly. We use pixel barycentric coordinates
for per sample shading. Instead we should select perspective sample
or non-perspective sample barycentric coordinates.

It also enables using sample barycentric coordinates in case of a
fragment shader variable declared with 'sample' qualifier.
e.g. sample in vec4 pos;

A piglit test to verify the implementation has been posted on piglit
mailing list for review.

V2: Do not interpolate all the 'in' variables at sample position
    if fragment shader uses 'sample' qualifier with one of them.
    For example we have a fragment shader:
    #version 330
    #extension ARB_gpu_shader5: require
    sample in vec4 a;
    in vec4 b;
    main()
    {
      ...
    }

    Only 'a' should be sampled at sample location, not 'b'.

Cc: [email protected]
Signed-off-by: Anuj Phogat <[email protected]>
Reviewed-by: Chris Forbes <[email protected]>

1 files changed, 10 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 78ddf0d99cf..430a530d242 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -998,7 +998,7 @@ fs_visitor::emit_fragcoord_interpolation(ir_variable *ir)
 fs_inst *
 fs_visitor::emit_linterp(const fs_reg &attr, const fs_reg &interp,
                          glsl_interp_qualifier interpolation_mode,
-                         bool is_centroid)
+                         bool is_centroid, bool is_sample)
 {
    brw_wm_barycentric_interp_mode barycoord_mode;
    if (brw->gen >= 6) {
@@ -1007,6 +1007,11 @@ fs_visitor::emit_linterp(const fs_reg &attr, const fs_reg &interp,
             barycoord_mode = BRW_WM_PERSPECTIVE_CENTROID_BARYCENTRIC;
          else
             barycoord_mode = BRW_WM_NONPERSPECTIVE_CENTROID_BARYCENTRIC;
+      } else if (is_sample) {
+          if (interpolation_mode == INTERP_QUALIFIER_SMOOTH)
+            barycoord_mode = BRW_WM_PERSPECTIVE_SAMPLE_BARYCENTRIC;
+         else
+            barycoord_mode = BRW_WM_NONPERSPECTIVE_SAMPLE_BARYCENTRIC;
       } else {
          if (interpolation_mode == INTERP_QUALIFIER_SMOOTH)
             barycoord_mode = BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC;
@@ -1084,7 +1089,8 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
 		*/
                struct brw_reg interp = interp_reg(location, k);
                emit_linterp(attr, fs_reg(interp), interpolation_mode,
-                            ir->data.centroid);
+                            ir->data.centroid,
+                            ir->data.sample || c->key.persample_shading);
                if (brw->needs_unlit_centroid_workaround && ir->data.centroid) {
                   /* Get the pixel/sample mask into f0 so that we know
                    * which pixels are lit.  Then, for each channel that is
@@ -1093,7 +1099,8 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
                    */
                   emit(FS_OPCODE_MOV_DISPATCH_TO_FLAGS);
                   fs_inst *inst = emit_linterp(attr, fs_reg(interp),
-                                               interpolation_mode, false);
+                                               interpolation_mode,
+                                               false, false);
                   inst->predicate = BRW_PREDICATE_NORMAL;
                   inst->predicate_inverse = true;
                }