draw: inject frontface info into wireframe outputs

Draw module can decompose primitives into wireframe models, which
is a fancy word for 'lines', unfortunately that decomposition means
that we weren't able to preserve the original front-face info which
could be derived from the original primitives (lines don't have a
'face'). To fix it allow draw module to inject a fake face semantic
into outputs from which the backends can figure out the original
frontfacing info of the primitives.

Signed-off-by: Zack Rusin <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>
Reviewed-by: Jose Fonseca <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/gallium/drivers/llvmpipe/lp_context.h b/src/gallium/drivers/llvmpipe/lp_context.h
index 9495e42feee..fc948a727fe 100644
--- a/src/gallium/drivers/llvmpipe/lp_context.h
+++ b/src/gallium/drivers/llvmpipe/lp_context.h
@@ -122,6 +122,9 @@ struct llvmpipe_context {
    /** Which geometry shader output slot contains layer */
    int layer_slot;
 
+   /** A fake frontface output for unfilled primitives */
+   int face_slot;
+
    /**< minimum resolvable depth value, for polygon offset */   
    double mrd;