src/gallium/auxiliary/draw/draw_pipe_wide_line.c

/**************************************************************************
 * 
 * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
 * 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 TUNGSTEN GRAPHICS 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 <keith@tungstengraphics.com>
 */

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


struct wideline_stage {
   struct draw_stage stage;

   float half_line_width;
};



static INLINE struct wideline_stage *wideline_stage( struct draw_stage *stage )
{
   return (struct wideline_stage *)stage;
}



/**
 * Draw a wide line by drawing a quad (two triangles).
 * XXX need to disable polygon stipple.
 */
static void wideline_line( struct draw_stage *stage,
                           struct prim_header *header )
{
   /*const struct wideline_stage *wide = wideline_stage(stage);*/
   const unsigned pos = stage->draw->vs.position_output;
   const float half_width = 0.5f * stage->draw->rasterizer->line_width;

   struct prim_header tri;

   struct vertex_header *v0 = dup_vert(stage, header->v[0], 0);
   struct vertex_header *v1 = dup_vert(stage, header->v[0], 1);
   struct vertex_header *v2 = dup_vert(stage, header->v[1], 2);
   struct vertex_header *v3 = dup_vert(stage, header->v[1], 3);

   float *pos0 = v0->data[pos];
   float *pos1 = v1->data[pos];
   float *pos2 = v2->data[pos];
   float *pos3 = v3->data[pos];

   const float dx = fabsf(pos0[0] - pos2[0]);
   const float dy = fabsf(pos0[1] - pos2[1]);

   /* small tweak to meet GL specification */
   const float bias = 0.125f;

   /*
    * Draw wide line as a quad (two tris) by "stretching" the line along
    * X or Y.
    * We need to tweak coords in several ways to be conformant here.
    */

   if (dx > dy) {
      /* x-major line */
      pos0[1] = pos0[1] - half_width - bias;
      pos1[1] = pos1[1] + half_width - bias;
      pos2[1] = pos2[1] - half_width - bias;
      pos3[1] = pos3[1] + half_width - bias;
      if (pos0[0] < pos2[0]) {
         /* left to right line */
         pos0[0] -= 0.5f;
         pos1[0] -= 0.5f;
         pos2[0] -= 0.5f;
         pos3[0] -= 0.5f;
      }
      else {
         /* right to left line */
         pos0[0] += 0.5f;
         pos1[0] += 0.5f;
         pos2[0] += 0.5f;
         pos3[0] += 0.5f;
      }
   }
   else {
      /* y-major line */
      pos0[0] = pos0[0] - half_width + bias;
      pos1[0] = pos1[0] + half_width + bias;
      pos2[0] = pos2[0] - half_width + bias;
      pos3[0] = pos3[0] + half_width + bias;
      if (pos0[1] < pos2[1]) {
         /* top to bottom line */
         pos0[1] -= 0.5f;
         pos1[1] -= 0.5f;
         pos2[1] -= 0.5f;
         pos3[1] -= 0.5f;
      }
      else {
         /* bottom to top line */
         pos0[1] += 0.5f;
         pos1[1] += 0.5f;
         pos2[1] += 0.5f;
         pos3[1] += 0.5f;
      }
   }

   tri.det = header->det;  /* only the sign matters */
   tri.v[0] = v0;
   tri.v[1] = v2;
   tri.v[2] = v3;
   stage->next->tri( stage->next, &tri );

   tri.v[0] = v0;
   tri.v[1] = v3;
   tri.v[2] = v1;
   stage->next->tri( stage->next, &tri );
}


static void wideline_flush( struct draw_stage *stage, unsigned flags )
{
   stage->next->flush( stage->next, flags );
}


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


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


struct draw_stage *draw_wide_line_stage( struct draw_context *draw )
{
   struct wideline_stage *wide = CALLOC_STRUCT(wideline_stage);

   draw_alloc_temp_verts( &wide->stage, 4 );

   wide->stage.draw = draw;
   wide->stage.name = "wide-line";
   wide->stage.next = NULL;
   wide->stage.point = draw_pipe_passthrough_point;
   wide->stage.line = wideline_line;
   wide->stage.tri = draw_pipe_passthrough_tri;
   wide->stage.flush = wideline_flush;
   wide->stage.reset_stipple_counter = wideline_reset_stipple_counter;
   wide->stage.destroy = wideline_destroy;

   return &wide->stage;
}