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]>

6 files changed, 39 insertions, 4 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;
    
diff --git a/src/gallium/drivers/llvmpipe/lp_setup.c b/src/gallium/drivers/llvmpipe/lp_setup.c
index 65f61edc360..5fde01fa13b 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup.c
@@ -1053,6 +1053,7 @@ lp_setup_update_state( struct lp_setup_context *setup,
       setup->psize = lp->psize_slot;
       setup->viewport_index_slot = lp->viewport_index_slot;
       setup->layer_slot = lp->layer_slot;
+      setup->face_slot = lp->face_slot;
 
       assert(lp->dirty == 0);
 
diff --git a/src/gallium/drivers/llvmpipe/lp_setup_context.h b/src/gallium/drivers/llvmpipe/lp_setup_context.h
index 89c23bbb3ac..ea1d0d688d8 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup_context.h
+++ b/src/gallium/drivers/llvmpipe/lp_setup_context.h
@@ -106,6 +106,7 @@ struct lp_setup_context
    float psize;
    unsigned viewport_index_slot;
    unsigned layer_slot;
+   unsigned face_slot;
 
    struct pipe_framebuffer_state fb;
    struct u_rect framebuffer;
diff --git a/src/gallium/drivers/llvmpipe/lp_setup_line.c b/src/gallium/drivers/llvmpipe/lp_setup_line.c
index bfed59cba0a..3b16163ba59 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup_line.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup_line.c
@@ -37,6 +37,7 @@
 #include "lp_state_fs.h"
 #include "lp_state_setup.h"
 #include "lp_context.h"
+#include "draw/draw_context.h"
 
 #define NUM_CHANNELS 4
 
@@ -45,6 +46,7 @@ struct lp_line_info {
    float dx;
    float dy;
    float oneoverarea;
+   boolean frontfacing;
 
    const float (*v1)[4];
    const float (*v2)[4];
@@ -214,7 +216,8 @@ static void setup_line_coefficients( struct lp_setup_context *setup,
       case LP_INTERP_FACING:
          for (i = 0; i < NUM_CHANNELS; i++)
             if (usage_mask & (1 << i))
-               constant_coef(setup, info, slot+1, 1.0, i);
+               constant_coef(setup, info, slot+1,
+                             info->frontfacing ? 1.0f : -1.0f, i);
          break;
 
       default:
@@ -613,15 +616,22 @@ try_setup_line( struct lp_setup_context *setup,
    plane[2].dcdx = y[2] - y[3];
    plane[3].dcdx = y[3] - y[0];
 
+   if (draw_will_inject_frontface(lp_context->draw) &&
+       setup->face_slot > 0) {
+      line->inputs.frontfacing = v1[setup->face_slot][0];
+   } else {
+      line->inputs.frontfacing = TRUE;
+   }
+   
 
    /* Setup parameter interpolants:
     */
    info.a0 = GET_A0(&line->inputs);
    info.dadx = GET_DADX(&line->inputs);
    info.dady = GET_DADY(&line->inputs);
+   info.frontfacing = line->inputs.frontfacing;
    setup_line_coefficients(setup, &info); 
 
-   line->inputs.frontfacing = TRUE;
    line->inputs.disable = FALSE;
    line->inputs.opaque = FALSE;
    line->inputs.layer = layer;
diff --git a/src/gallium/drivers/llvmpipe/lp_setup_point.c b/src/gallium/drivers/llvmpipe/lp_setup_point.c
index 868a9a904b7..cbcc8d4f2f3 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup_point.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup_point.c
@@ -38,6 +38,7 @@
 #include "lp_state_setup.h"
 #include "lp_context.h"
 #include "tgsi/tgsi_scan.h"
+#include "draw/draw_context.h"
 
 #define NUM_CHANNELS 4
 
@@ -51,6 +52,8 @@ struct point_info {
    float (*a0)[4];
    float (*dadx)[4];
    float (*dady)[4];
+
+   boolean frontfacing;
 };   
 
 
@@ -276,7 +279,8 @@ setup_point_coefficients( struct lp_setup_context *setup,
       case LP_INTERP_FACING:
          for (i = 0; i < NUM_CHANNELS; i++)
             if (usage_mask & (1 << i))
-               constant_coef(setup, info, slot+1, 1.0, i);
+               constant_coef(setup, info, slot+1,
+                             info->frontfacing ? 1.0f : -1.0f, i);
          break;
 
       default:
@@ -384,6 +388,13 @@ try_setup_point( struct lp_setup_context *setup,
       lp_context->pipeline_statistics.c_primitives++;
    }
 
+   if (draw_will_inject_frontface(lp_context->draw) &&
+       setup->face_slot > 0) {
+      point->inputs.frontfacing = v0[setup->face_slot][0];
+   } else {
+      point->inputs.frontfacing = TRUE;
+   }
+
    info.v0 = v0;
    info.dx01 = 0;
    info.dx12 = fixed_width;
@@ -392,12 +403,12 @@ try_setup_point( struct lp_setup_context *setup,
    info.a0 = GET_A0(&point->inputs);
    info.dadx = GET_DADX(&point->inputs);
    info.dady = GET_DADY(&point->inputs);
+   info.frontfacing = point->inputs.frontfacing;
    
    /* Setup parameter interpolants:
     */
    setup_point_coefficients(setup, &info);
 
-   point->inputs.frontfacing = TRUE;
    point->inputs.disable = FALSE;
    point->inputs.opaque = FALSE;
    point->inputs.layer = layer;
diff --git a/src/gallium/drivers/llvmpipe/lp_state_derived.c b/src/gallium/drivers/llvmpipe/lp_state_derived.c
index dc80358c7be..5a51b50821e 100644
--- a/src/gallium/drivers/llvmpipe/lp_state_derived.c
+++ b/src/gallium/drivers/llvmpipe/lp_state_derived.c
@@ -53,6 +53,8 @@ compute_vertex_info(struct llvmpipe_context *llvmpipe)
    int vs_index;
    uint i;
 
+   draw_prepare_shader_outputs(llvmpipe->draw);
+
    llvmpipe->color_slot[0] = -1;
    llvmpipe->color_slot[1] = -1;
    llvmpipe->bcolor_slot[0] = -1;
@@ -138,6 +140,13 @@ compute_vertex_info(struct llvmpipe_context *llvmpipe)
       llvmpipe->layer_slot = 0;
    }
 
+   /* Check for a fake front face for unfilled primitives*/
+   vs_index = draw_find_shader_output(llvmpipe->draw,
+                                      TGSI_SEMANTIC_FACE, 0);
+   if (vs_index >= 0) {
+      llvmpipe->face_slot = vinfo->num_attribs;
+      draw_emit_vertex_attr(vinfo, EMIT_4F, INTERP_CONSTANT, vs_index);
+   }
 
    draw_compute_vertex_size(vinfo);
    lp_setup_set_vertex_info(llvmpipe->setup, vinfo);