Implement gl_FrontFacing for fragment shaders.

For the time being, we put the gl_FrontFacing value in the FOGC.Y input
register.  Combining FOGC and FrontFacing in one register is a bit of a
hack and may need to be changed someday.

2 files changed, 4 insertions, 3 deletions

diff --git a/src/mesa/swrast_setup/ss_triangle.c b/src/mesa/swrast_setup/ss_triangle.c
index 09244d9c4b..628e9288e8 100644
--- a/src/mesa/swrast_setup/ss_triangle.c
+++ b/src/mesa/swrast_setup/ss_triangle.c
@@ -290,8 +290,10 @@ void _swsetup_choose_trifuncs( GLcontext *ctx )
        ctx->Polygon.OffsetFill)
       ind |= SS_OFFSET_BIT;
 
+   /* Note: gl_FrontFacing lives in fragment input FOGC.Y at this time */
    if ((ctx->Light.Enabled && ctx->Light.Model.TwoSide) ||
-       (ctx->VertexProgram._Enabled && ctx->VertexProgram.TwoSideEnabled))
+       (ctx->VertexProgram._Enabled && ctx->VertexProgram.TwoSideEnabled) ||
+       (ctx->FragmentProgram._Current && ctx->FragmentProgram._Current->Base.InputsRead & (1 << FRAG_ATTRIB_FOGC)))
       ind |= SS_TWOSIDE_BIT;
 
    /* We piggyback the two-sided stencil front/back determination on the
diff --git a/src/mesa/swrast_setup/ss_tritmp.h b/src/mesa/swrast_setup/ss_tritmp.h
index 61c9b2817e..5b14b283f1 100644
--- a/src/mesa/swrast_setup/ss_tritmp.h
+++ b/src/mesa/swrast_setup/ss_tritmp.h
@@ -55,8 +55,7 @@ static void TAG(triangle)(GLcontext *ctx, GLuint e0, GLuint e1, GLuint e2 )
       if (IND & (SS_TWOSIDE_BIT | SS_UNFILLED_BIT))
       {
 	 facing = (cc < 0.0) ^ ctx->Polygon._FrontBit;
-         if (ctx->Stencil.TestTwoSide)
-            ctx->_Facing = facing; /* for 2-sided stencil test */
+         ctx->_Facing = facing;
 
 	 if (IND & SS_UNFILLED_BIT)
 	    mode = facing ? ctx->Polygon.BackMode : ctx->Polygon.FrontMode;