gallivm/llvmpipe: added lp_rast_shader_inputs::facing and pass through

The triangle rasterizer sets this field to indicate front/back-facing.
It gets passed into the generated fragment code as another parameter.
Used now for stencil front/back selection but will also be used for
fragment shaders in general (see TGSI_SEMANTIC_FACE).

With this commit two-sided stenciling mostly works but there's
still a bug or two...

1 files changed, 2 insertions, 0 deletions

diff --git a/src/gallium/drivers/llvmpipe/lp_rast.h b/src/gallium/drivers/llvmpipe/lp_rast.h
index 303f6e3f7e4..ae838f3fbef 100644
--- a/src/gallium/drivers/llvmpipe/lp_rast.h
+++ b/src/gallium/drivers/llvmpipe/lp_rast.h
@@ -82,6 +82,8 @@ struct lp_rast_state {
  * These pointers point into the bin data buffer.
  */
 struct lp_rast_shader_inputs {
+   float facing;     /** Positive for front-facing, negative for back-facing */
+
    float (*a0)[4];
    float (*dadx)[4];
    float (*dady)[4];