src/gallium/auxiliary/draw/draw_pipe_twoside.c

/**************************************************************************
 *
 * Copyright 2007 VMware, Inc.
 * All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sub license, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial portions
 * of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
 * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
 * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 **************************************************************************/

/* Authors:  Keith Whitwell <keithw@vmware.com>
 */

#include "util/u_math.h"
#include "util/u_memory.h"
#include "pipe/p_defines.h"
#include "pipe/p_shader_tokens.h"
#include "draw_vs.h"
#include "draw_pipe.h"

struct twoside_stage {
   struct draw_stage stage;
   float sign;         /**< +1 or -1 */
   int attrib_front0, attrib_back0;
   int attrib_front1, attrib_back1;
};


static inline struct twoside_stage *
twoside_stage(struct draw_stage *stage)
{
   return (struct twoside_stage *) stage;
}


/**
 * Copy back color(s) to front color(s).
 */
static inline struct vertex_header *
copy_bfc(struct twoside_stage *twoside,
         const struct vertex_header *v,
         unsigned idx)
{
   struct vertex_header *tmp = dup_vert(&twoside->stage, v, idx);

   if (twoside->attrib_back0 >= 0 && twoside->attrib_front0 >= 0) {
      COPY_4FV(tmp->data[twoside->attrib_front0],
               tmp->data[twoside->attrib_back0]);
   }
   if (twoside->attrib_back1 >= 0 && twoside->attrib_front1 >= 0) {
      COPY_4FV(tmp->data[twoside->attrib_front1],
               tmp->data[twoside->attrib_back1]);
   }

   return tmp;
}


/* Twoside tri:
 */
static void
twoside_tri(struct draw_stage *stage,
            struct prim_header *header)
{
   struct twoside_stage *twoside = twoside_stage(stage);

   if (header->det * twoside->sign < 0.0) {
      /* this is a back-facing triangle */
      struct prim_header tmp;

      tmp.det = header->det;
      tmp.flags = header->flags;
      tmp.pad = header->pad;
      /* copy back attribs to front attribs */
      tmp.v[0] = copy_bfc(twoside, header->v[0], 0);
      tmp.v[1] = copy_bfc(twoside, header->v[1], 1);
      tmp.v[2] = copy_bfc(twoside, header->v[2], 2);

      stage->next->tri(stage->next, &tmp);
   } else {
      stage->next->tri(stage->next, header);
   }
}


static void
twoside_first_tri(struct draw_stage *stage,
                  struct prim_header *header)
{
   struct twoside_stage *twoside = twoside_stage(stage);
   const struct draw_vertex_shader *vs = stage->draw->vs.vertex_shader;

   twoside->attrib_front0 = -1;
   twoside->attrib_front1 = -1;
   twoside->attrib_back0 = -1;
   twoside->attrib_back1 = -1;

   /*
    * Find which vertex shader outputs are front/back colors
    * (only first two can be front or back).
    */
   for (unsigned i = 0; i < vs->info.num_outputs; i++) {
      if (vs->info.output_semantic_name[i] == TGSI_SEMANTIC_COLOR) {
         if (vs->info.output_semantic_index[i] == 0)
            twoside->attrib_front0 = i;
         else if (vs->info.output_semantic_index[i] == 1)
            twoside->attrib_front1 = i;
      }
      if (vs->info.output_semantic_name[i] == TGSI_SEMANTIC_BCOLOR) {
         if (vs->info.output_semantic_index[i] == 0)
            twoside->attrib_back0 = i;
         else if (vs->info.output_semantic_index[i] == 1)
            twoside->attrib_back1 = i;
      }
   }

   /*
    * We'll multiply the primitive's determinant by this sign to determine
    * if the triangle is back-facing (negative).
    * sign = -1 for CCW, +1 for CW
    */
   twoside->sign = stage->draw->rasterizer->front_ccw ? -1.0f : 1.0f;

   stage->tri = twoside_tri;
   stage->tri(stage, header);
}


static void
twoside_flush(struct draw_stage *stage, unsigned flags)
{
   stage->tri = twoside_first_tri;
   stage->next->flush(stage->next, flags);
}


static void
twoside_reset_stipple_counter(struct draw_stage *stage)
{
   stage->next->reset_stipple_counter(stage->next);
}


static void
twoside_destroy(struct draw_stage *stage)
{
   draw_free_temp_verts(stage);
   FREE(stage);
}


/**
 * Create twoside pipeline stage.
 */
struct draw_stage *
draw_twoside_stage(struct draw_context *draw)
{
   struct twoside_stage *twoside = CALLOC_STRUCT(twoside_stage);
   if (!twoside)
      goto fail;

   twoside->stage.draw = draw;
   twoside->stage.name = "twoside";
   twoside->stage.next = NULL;
   twoside->stage.point = draw_pipe_passthrough_point;
   twoside->stage.line = draw_pipe_passthrough_line;
   twoside->stage.tri = twoside_first_tri;
   twoside->stage.flush = twoside_flush;
   twoside->stage.reset_stipple_counter = twoside_reset_stipple_counter;
   twoside->stage.destroy = twoside_destroy;

   if (!draw_alloc_temp_verts(&twoside->stage, 3))
      goto fail;

   return &twoside->stage;

fail:
   if (twoside)
      twoside->stage.destroy(&twoside->stage);

   return NULL;
}