lp_setup_line.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.
 *
 **************************************************************************/

/*
 * Binning code for lines
 */

#include "util/u_math.h"
#include "util/u_memory.h"
#include "lp_perf.h"
#include "lp_setup_context.h"
#include "lp_rast.h"
#include "lp_state_fs.h"
#include "lp_state_setup.h"
#include "lp_context.h"
#include "draw/draw_context.h"

#define NUM_CHANNELS 4

struct lp_line_info {

   float dx;
   float dy;
   float oneoverarea;
   boolean frontfacing;

   const float (*v1)[4];
   const float (*v2)[4];

   float (*a0)[4];
   float (*dadx)[4];
   float (*dady)[4];
};


/**
 * Compute a0 for a constant-valued coefficient (GL_FLAT shading).
 */
static void constant_coef( struct lp_setup_context *setup,
                           struct lp_line_info *info,
                           unsigned slot,
                           const float value,
                           unsigned i )
{
   info->a0[slot][i] = value;
   info->dadx[slot][i] = 0.0f;
   info->dady[slot][i] = 0.0f;
}


/**
 * Compute a0, dadx and dady for a linearly interpolated coefficient,
 * for a triangle.
 */
static void linear_coef( struct lp_setup_context *setup,
                         struct lp_line_info *info,
                         unsigned slot,
                         unsigned vert_attr,
                         unsigned i)
{
   float a1 = info->v1[vert_attr][i]; 
   float a2 = info->v2[vert_attr][i];
      
   float da21 = a1 - a2;   
   float dadx = da21 * info->dx * info->oneoverarea;
   float dady = da21 * info->dy * info->oneoverarea;

   info->dadx[slot][i] = dadx;
   info->dady[slot][i] = dady;  
   
   info->a0[slot][i] = (a1 -
                              (dadx * (info->v1[0][0] - setup->pixel_offset) +
                               dady * (info->v1[0][1] - setup->pixel_offset)));
}


/**
 * Compute a0, dadx and dady for a perspective-corrected interpolant,
 * for a triangle.
 * We basically multiply the vertex value by 1/w before computing
 * the plane coefficients (a0, dadx, dady).
 * Later, when we compute the value at a particular fragment position we'll
 * divide the interpolated value by the interpolated W at that fragment.
 */
static void perspective_coef( struct lp_setup_context *setup,
                              struct lp_line_info *info,
                              unsigned slot,
                              unsigned vert_attr,
                              unsigned i)
{
   /* premultiply by 1/w  (v[0][3] is always 1/w):
    */
   float a1 = info->v1[vert_attr][i] * info->v1[0][3];
   float a2 = info->v2[vert_attr][i] * info->v2[0][3];

   float da21 = a1 - a2;   
   float dadx = da21 * info->dx * info->oneoverarea;
   float dady = da21 * info->dy * info->oneoverarea;

   info->dadx[slot][i] = dadx;
   info->dady[slot][i] = dady;
   
   info->a0[slot][i] = (a1 -
                        (dadx * (info->v1[0][0] - setup->pixel_offset) +
                         dady * (info->v1[0][1] - setup->pixel_offset)));
}

static void
setup_fragcoord_coef( struct lp_setup_context *setup,
                      struct lp_line_info *info,
                      unsigned slot,
                      unsigned usage_mask)
{
   /*X*/
   if (usage_mask & TGSI_WRITEMASK_X) {
      info->a0[slot][0] = 0.0;
      info->dadx[slot][0] = 1.0;
      info->dady[slot][0] = 0.0;
   }

   /*Y*/
   if (usage_mask & TGSI_WRITEMASK_Y) {
      info->a0[slot][1] = 0.0;
      info->dadx[slot][1] = 0.0;
      info->dady[slot][1] = 1.0;
   }

   /*Z*/
   if (usage_mask & TGSI_WRITEMASK_Z) {
      linear_coef(setup, info, slot, 0, 2);
   }

   /*W*/
   if (usage_mask & TGSI_WRITEMASK_W) {
      linear_coef(setup, info, slot, 0, 3);
   }
}

/**
 * Compute the tri->coef[] array dadx, dady, a0 values.
 */
static void setup_line_coefficients( struct lp_setup_context *setup,
                                     struct lp_line_info *info)
{
   const struct lp_setup_variant_key *key = &setup->setup.variant->key;
   unsigned fragcoord_usage_mask = TGSI_WRITEMASK_XYZ;
   unsigned slot;

   /* setup interpolation for all the remaining attributes:
    */
   for (slot = 0; slot < key->num_inputs; slot++) {
      unsigned vert_attr = key->inputs[slot].src_index;
      unsigned usage_mask = key->inputs[slot].usage_mask;
      unsigned i;
           
      switch (key->inputs[slot].interp) {
      case LP_INTERP_CONSTANT:
         if (key->flatshade_first) {
            for (i = 0; i < NUM_CHANNELS; i++)
               if (usage_mask & (1 << i))
                  constant_coef(setup, info, slot+1, info->v1[vert_attr][i], i);
         }
         else {
            for (i = 0; i < NUM_CHANNELS; i++)
               if (usage_mask & (1 << i))
                  constant_coef(setup, info, slot+1, info->v2[vert_attr][i], i);
         }
         break;

      case LP_INTERP_LINEAR:
         for (i = 0; i < NUM_CHANNELS; i++)
            if (usage_mask & (1 << i))
               linear_coef(setup, info, slot+1, vert_attr, i);
         break;

      case LP_INTERP_PERSPECTIVE:
         for (i = 0; i < NUM_CHANNELS; i++)
            if (usage_mask & (1 << i))
               perspective_coef(setup, info, slot+1, vert_attr, i);
         fragcoord_usage_mask |= TGSI_WRITEMASK_W;
         break;

      case LP_INTERP_POSITION:
         /*
          * The generated pixel interpolators will pick up the coeffs from
          * slot 0, so all need to ensure that the usage mask is covers all
          * usages.
          */
         fragcoord_usage_mask |= usage_mask;
         break;

      case LP_INTERP_FACING:
         for (i = 0; i < NUM_CHANNELS; i++)
            if (usage_mask & (1 << i))
               constant_coef(setup, info, slot+1,
                             info->frontfacing ? 1.0f : -1.0f, i);
         break;

      default:
         assert(0);
      }
   }

   /* The internal position input is in slot zero:
    */
   setup_fragcoord_coef(setup, info, 0,
                        fragcoord_usage_mask);
}



static inline int subpixel_snap( float a )
{
   return util_iround(FIXED_ONE * a);
}


/**
 * Print line vertex attribs (for debug).
 */
static void
print_line(struct lp_setup_context *setup,
           const float (*v1)[4],
           const float (*v2)[4])
{
   const struct lp_setup_variant_key *key = &setup->setup.variant->key;
   uint i;

   debug_printf("llvmpipe line\n");
   for (i = 0; i < 1 + key->num_inputs; i++) {
      debug_printf("  v1[%d]:  %f %f %f %f\n", i,
                   v1[i][0], v1[i][1], v1[i][2], v1[i][3]);
   }
   for (i = 0; i < 1 + key->num_inputs; i++) {
      debug_printf("  v2[%d]:  %f %f %f %f\n", i,
                   v2[i][0], v2[i][1], v2[i][2], v2[i][3]);
   }
}


static inline boolean sign(float x){
   return x >= 0;  
}  


/* Used on positive floats only:
 */
static inline float fracf(float f)
{
   return f - floorf(f);
}



static boolean
try_setup_line( struct lp_setup_context *setup,
               const float (*v1)[4],
               const float (*v2)[4])
{
   struct llvmpipe_context *lp_context = (struct llvmpipe_context *)setup->pipe;
   struct lp_scene *scene = setup->scene;
   const struct lp_setup_variant_key *key = &setup->setup.variant->key;
   struct lp_rast_triangle *line;
   struct lp_rast_plane *plane;
   struct lp_line_info info;
   float width = MAX2(1.0, setup->line_width);
   const struct u_rect *scissor;
   struct u_rect bbox, bboxpos;
   boolean s_planes[4];
   unsigned tri_bytes;
   int x[4]; 
   int y[4];
   int i;
   int nr_planes = 4;
   unsigned viewport_index = 0;
   unsigned layer = 0;
   float pixel_offset = setup->multisample ? 0.0 : setup->pixel_offset;
   /* linewidth should be interpreted as integer */
   int fixed_width = util_iround(width) * FIXED_ONE;

   float x_offset=0;
   float y_offset=0;
   float x_offset_end=0;
   float y_offset_end=0;
      
   float x1diff;
   float y1diff;
   float x2diff;
   float y2diff;
   float dx, dy;
   float area;
   const float (*pv)[4];

   boolean draw_start;
   boolean draw_end;
   boolean will_draw_start;
   boolean will_draw_end;

   if (lp_context->active_statistics_queries) {
      lp_context->pipeline_statistics.c_primitives++;
   }

   if (0)
      print_line(setup, v1, v2);

   if (setup->flatshade_first) {
      pv = v1;
   }
   else {
      pv = v2;
   }
   if (setup->viewport_index_slot > 0) {
      unsigned *udata = (unsigned*)pv[setup->viewport_index_slot];
      viewport_index = lp_clamp_viewport_idx(*udata);
   }
   if (setup->layer_slot > 0) {
      layer = *(unsigned*)pv[setup->layer_slot];
      layer = MIN2(layer, scene->fb_max_layer);
   }

   dx = v1[0][0] - v2[0][0];
   dy = v1[0][1] - v2[0][1];
   area = (dx * dx  + dy * dy);
   if (area == 0) {
      LP_COUNT(nr_culled_tris);
      return TRUE;
   }

   info.oneoverarea = 1.0f / area;
   info.dx = dx;
   info.dy = dy;
   info.v1 = v1;
   info.v2 = v2;

  
   if (setup->rectangular_lines) {
      float scale = (setup->line_width * 0.5f) / sqrtf(area);
      int tx = subpixel_snap(-dy * scale);
      int ty = subpixel_snap(+dx * scale);

      x[0] = subpixel_snap(v1[0][0] - pixel_offset) - tx;
      x[1] = subpixel_snap(v2[0][0] - pixel_offset) - tx;
      x[2] = subpixel_snap(v2[0][0] - pixel_offset) + tx;
      x[3] = subpixel_snap(v1[0][0] - pixel_offset) + tx;

      y[0] = subpixel_snap(v1[0][1] - pixel_offset) - ty;
      y[1] = subpixel_snap(v2[0][1] - pixel_offset) - ty;
      y[2] = subpixel_snap(v2[0][1] - pixel_offset) + ty;
      y[3] = subpixel_snap(v1[0][1] - pixel_offset) + ty;
   } else if (fabsf(dx) >= fabsf(dy)) {
      float dydx = dy / dx;

      /* X-MAJOR LINE */
      x1diff = v1[0][0] - floorf(v1[0][0]) - 0.5f;
      y1diff = v1[0][1] - floorf(v1[0][1]) - 0.5f;
      x2diff = v2[0][0] - floorf(v2[0][0]) - 0.5f;
      y2diff = v2[0][1] - floorf(v2[0][1]) - 0.5f;

      if (y2diff==-0.5 && dy<0){
         y2diff = 0.5;
      }
      
      /* 
       * Diamond exit rule test for starting point 
       */    
      if (fabsf(x1diff) + fabsf(y1diff) < 0.5) {
         draw_start = TRUE;
      }
      else if (sign(x1diff) == sign(-dx)) {
         draw_start = FALSE;
      }
      else if (sign(-y1diff) != sign(dy)) {
         draw_start = TRUE;
      }
      else {
         /* do intersection test */
         float yintersect = fracf(v1[0][1]) + x1diff * dydx;
         draw_start = (yintersect < 1.0 && yintersect > 0.0);
      }


      /* 
       * Diamond exit rule test for ending point 
       */    
      if (fabsf(x2diff) + fabsf(y2diff) < 0.5) {
         draw_end = FALSE;
      }
      else if (sign(x2diff) != sign(-dx)) {
         draw_end = FALSE;
      }
      else if (sign(-y2diff) == sign(dy)) {
         draw_end = TRUE;
      }
      else {
         /* do intersection test */
         float yintersect = fracf(v2[0][1]) + x2diff * dydx;
         draw_end = (yintersect < 1.0 && yintersect > 0.0);
      }

      /* Are we already drawing start/end?
       */
      will_draw_start = sign(-x1diff) != sign(dx);
      will_draw_end = (sign(x2diff) == sign(-dx)) || x2diff==0;

      if (dx < 0) {
         /* if v2 is to the right of v1, swap pointers */
         const float (*temp)[4] = v1;
         v1 = v2;
         v2 = temp;
         dx = -dx;
         dy = -dy;
         /* Otherwise shift planes appropriately */
         if (will_draw_start != draw_start) {
            x_offset_end = - x1diff - 0.5;
            y_offset_end = x_offset_end * dydx;

         }
         if (will_draw_end != draw_end) {
            x_offset = - x2diff - 0.5;
            y_offset = x_offset * dydx;
         }

      }
      else{
         /* Otherwise shift planes appropriately */
         if (will_draw_start != draw_start) {
            x_offset = - x1diff + 0.5;
            y_offset = x_offset * dydx;
         }
         if (will_draw_end != draw_end) {
            x_offset_end = - x2diff + 0.5;
            y_offset_end = x_offset_end * dydx;
         }
      }
  
      /* x/y positions in fixed point */
      x[0] = subpixel_snap(v1[0][0] + x_offset     - pixel_offset);
      x[1] = subpixel_snap(v2[0][0] + x_offset_end - pixel_offset);
      x[2] = subpixel_snap(v2[0][0] + x_offset_end - pixel_offset);
      x[3] = subpixel_snap(v1[0][0] + x_offset     - pixel_offset);
      
      y[0] = subpixel_snap(v1[0][1] + y_offset     - pixel_offset) - fixed_width/2;
      y[1] = subpixel_snap(v2[0][1] + y_offset_end - pixel_offset) - fixed_width/2;
      y[2] = subpixel_snap(v2[0][1] + y_offset_end - pixel_offset) + fixed_width/2;
      y[3] = subpixel_snap(v1[0][1] + y_offset     - pixel_offset) + fixed_width/2;
      
   }
   else {
      const float dxdy = dx / dy;

      /* Y-MAJOR LINE */      
      x1diff = v1[0][0] - floorf(v1[0][0]) - 0.5f;
      y1diff = v1[0][1] - floorf(v1[0][1]) - 0.5f;
      x2diff = v2[0][0] - floorf(v2[0][0]) - 0.5f;
      y2diff = v2[0][1] - floorf(v2[0][1]) - 0.5f;

      if (x2diff==-0.5 && dx<0) {
         x2diff = 0.5;
      }

      /* 
       * Diamond exit rule test for starting point 
       */    
      if (fabsf(x1diff) + fabsf(y1diff) < 0.5) {
         draw_start = TRUE;
      }
      else if (sign(-y1diff) == sign(dy)) {
         draw_start = FALSE;
      }
      else if (sign(x1diff) != sign(-dx)) {
         draw_start = TRUE;
      }
      else {
         /* do intersection test */
         float xintersect = fracf(v1[0][0]) + y1diff * dxdy;
         draw_start = (xintersect < 1.0 && xintersect > 0.0);
      }

      /* 
       * Diamond exit rule test for ending point 
       */    
      if (fabsf(x2diff) + fabsf(y2diff) < 0.5) {
         draw_end = FALSE;
      }
      else if (sign(-y2diff) != sign(dy) ) {
         draw_end = FALSE;
      }
      else if (sign(x2diff) == sign(-dx) ) {
         draw_end = TRUE;
      }
      else {
         /* do intersection test */
         float xintersect = fracf(v2[0][0]) + y2diff * dxdy;
         draw_end = (xintersect < 1.0 && xintersect >= 0.0);
      }

      /* Are we already drawing start/end?
       */
      will_draw_start = sign(y1diff) == sign(dy);
      will_draw_end = (sign(-y2diff) == sign(dy)) || y2diff==0;

      if (dy > 0) {
         /* if v2 is on top of v1, swap pointers */
         const float (*temp)[4] = v1;
         v1 = v2;
         v2 = temp; 
         dx = -dx;
         dy = -dy;

         /* Otherwise shift planes appropriately */
         if (will_draw_start != draw_start) {
            y_offset_end = - y1diff + 0.5;
            x_offset_end = y_offset_end * dxdy;
         }
         if (will_draw_end != draw_end) {
            y_offset = - y2diff + 0.5;
            x_offset = y_offset * dxdy;
         }
      }
      else {
         /* Otherwise shift planes appropriately */
         if (will_draw_start != draw_start) {
            y_offset = - y1diff - 0.5;
            x_offset = y_offset * dxdy;
                     
         }
         if (will_draw_end != draw_end) {
            y_offset_end = - y2diff - 0.5;
            x_offset_end = y_offset_end * dxdy;
         }
      }

      /* x/y positions in fixed point */
      x[0] = subpixel_snap(v1[0][0] + x_offset     - pixel_offset) - fixed_width/2;
      x[1] = subpixel_snap(v2[0][0] + x_offset_end - pixel_offset) - fixed_width/2;
      x[2] = subpixel_snap(v2[0][0] + x_offset_end - pixel_offset) + fixed_width/2;
      x[3] = subpixel_snap(v1[0][0] + x_offset     - pixel_offset) + fixed_width/2;
     
      y[0] = subpixel_snap(v1[0][1] + y_offset     - pixel_offset);
      y[1] = subpixel_snap(v2[0][1] + y_offset_end - pixel_offset);
      y[2] = subpixel_snap(v2[0][1] + y_offset_end - pixel_offset);
      y[3] = subpixel_snap(v1[0][1] + y_offset     - pixel_offset);
   }

   /* Bounding rectangle (in pixels) */
   {
      /* Yes this is necessary to accurately calculate bounding boxes
       * with the two fill-conventions we support.  GL (normally) ends
       * up needing a bottom-left fill convention, which requires
       * slightly different rounding.
       */
      int adj = (setup->bottom_edge_rule != 0) ? 1 : 0;

      bbox.x0 = (MIN4(x[0], x[1], x[2], x[3]) + (FIXED_ONE-1)) >> FIXED_ORDER;
      bbox.x1 = (MAX4(x[0], x[1], x[2], x[3]) + (FIXED_ONE-1)) >> FIXED_ORDER;
      bbox.y0 = (MIN4(y[0], y[1], y[2], y[3]) + (FIXED_ONE-1) + adj) >> FIXED_ORDER;
      bbox.y1 = (MAX4(y[0], y[1], y[2], y[3]) + (FIXED_ONE-1) + adj) >> FIXED_ORDER;

      /* Inclusive coordinates:
       */
      bbox.x1--;
      bbox.y1--;
   }

   if (bbox.x1 < bbox.x0 ||
       bbox.y1 < bbox.y0) {
      if (0) debug_printf("empty bounding box\n");
      LP_COUNT(nr_culled_tris);
      return TRUE;
   }

   if (!u_rect_test_intersection(&setup->draw_regions[viewport_index], &bbox)) {
      if (0) debug_printf("offscreen\n");
      LP_COUNT(nr_culled_tris);
      return TRUE;
   }

   bboxpos = bbox;

   /* Can safely discard negative regions:
    */
   bboxpos.x0 = MAX2(bboxpos.x0, 0);
   bboxpos.y0 = MAX2(bboxpos.y0, 0);

   nr_planes = 4;
   /*
    * Determine how many scissor planes we need, that is drop scissor
    * edges if the bounding box of the tri is fully inside that edge.
    */
   scissor = &setup->draw_regions[viewport_index];
   scissor_planes_needed(s_planes, &bboxpos, scissor);
   nr_planes += s_planes[0] + s_planes[1] + s_planes[2] + s_planes[3];

   line = lp_setup_alloc_triangle(scene,
                                  key->num_inputs,
                                  nr_planes,
                                  &tri_bytes);
   if (!line)
      return FALSE;

#ifdef DEBUG
   line->v[0][0] = v1[0][0];
   line->v[1][0] = v2[0][0];   
   line->v[0][1] = v1[0][1];
   line->v[1][1] = v2[0][1];
#endif

   LP_COUNT(nr_tris);

   /* calculate the deltas */
   plane = GET_PLANES(line);
   plane[0].dcdy = x[0] - x[1];
   plane[1].dcdy = x[1] - x[2];
   plane[2].dcdy = x[2] - x[3];
   plane[3].dcdy = x[3] - x[0];

   plane[0].dcdx = y[0] - y[1];
   plane[1].dcdx = y[1] - y[2];
   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.disable = FALSE;
   line->inputs.opaque = FALSE;
   line->inputs.layer = layer;
   line->inputs.viewport_index = viewport_index;
   line->inputs.view_index = setup->view_index;

   /*
    * XXX: this code is mostly identical to the one in lp_setup_tri, except it
    * uses 4 planes instead of 3. Could share the code (including the sse
    * assembly, in fact we'd get the 4th plane for free).
    * The only difference apart from storing the 4th plane would be some
    * different shuffle for calculating dcdx/dcdy.
    */
   for (i = 0; i < 4; i++) {

      /* half-edge constants, will be iterated over the whole render
       * target.
       */
      plane[i].c = IMUL64(plane[i].dcdx, x[i]) - IMUL64(plane[i].dcdy, y[i]);

      /* correct for top-left vs. bottom-left fill convention.
       */
      if (plane[i].dcdx < 0) {
         /* both fill conventions want this - adjust for left edges */
         plane[i].c++;
      }
      else if (plane[i].dcdx == 0) {
         if (setup->bottom_edge_rule == 0) {
            /* correct for top-left fill convention:
             */
            if (plane[i].dcdy > 0) plane[i].c++;
         }
         else {
            /* correct for bottom-left fill convention:
             */
            if (plane[i].dcdy < 0) plane[i].c++;
         }
      }

      plane[i].dcdx *= FIXED_ONE;
      plane[i].dcdy *= FIXED_ONE;

      /* find trivial reject offsets for each edge for a single-pixel
       * sized block.  These will be scaled up at each recursive level to
       * match the active blocksize.  Scaling in this way works best if
       * the blocks are square.
       */
      plane[i].eo = 0;
      if (plane[i].dcdx < 0) plane[i].eo -= plane[i].dcdx;
      if (plane[i].dcdy > 0) plane[i].eo += plane[i].dcdy;
   }


   /* 
    * When rasterizing scissored tris, use the intersection of the
    * triangle bounding box and the scissor rect to generate the
    * scissor planes.
    *
    * This permits us to cut off the triangle "tails" that are present
    * in the intermediate recursive levels caused when two of the
    * triangles edges don't diverge quickly enough to trivially reject
    * exterior blocks from the triangle.
    *
    * It's not really clear if it's worth worrying about these tails,
    * but since we generate the planes for each scissored tri, it's
    * free to trim them in this case.
    * 
    * Note that otherwise, the scissor planes only vary in 'C' value,
    * and even then only on state-changes.  Could alternatively store
    * these planes elsewhere.
    * (Or only store the c value together with a bit indicating which
    * scissor edge this is, so rasterization would treat them differently
    * (easier to evaluate) to ordinary planes.)
    */
   if (nr_planes > 4) {
      struct lp_rast_plane *plane_s = &plane[4];

      if (s_planes[0]) {
         plane_s->dcdx = ~0U << 8;
         plane_s->dcdy = 0;
         plane_s->c = (1-scissor->x0) << 8;
         plane_s->eo = 1 << 8;
         plane_s++;
      }
      if (s_planes[1]) {
         plane_s->dcdx = 1 << 8;
         plane_s->dcdy = 0;
         plane_s->c = (scissor->x1+1) << 8;
         plane_s->eo = 0 << 8;
         plane_s++;
      }
      if (s_planes[2]) {
         plane_s->dcdx = 0;
         plane_s->dcdy = 1 << 8;
         plane_s->c = (1-scissor->y0) << 8;
         plane_s->eo = 1 << 8;
         plane_s++;
      }
      if (s_planes[3]) {
         plane_s->dcdx = 0;
         plane_s->dcdy = ~0U << 8;
         plane_s->c = (scissor->y1+1) << 8;
         plane_s->eo = 0;
         plane_s++;
      }
      assert(plane_s == &plane[nr_planes]);
   }

   return lp_setup_bin_triangle(setup, line, &bbox, &bboxpos, nr_planes, viewport_index);
}


static void lp_setup_line_discard(struct lp_setup_context *setup,
                                  const float (*v0)[4],
                                  const float (*v1)[4])
{
}

static void lp_setup_line(struct lp_setup_context *setup,
                          const float (*v0)[4],
                          const float (*v1)[4])
{
   if (!try_setup_line(setup, v0, v1)) {
      if (!lp_setup_flush_and_restart(setup))
         return;

      if (!try_setup_line(setup, v0, v1))
         return;
   }
}


void lp_setup_choose_line(struct lp_setup_context *setup)
{ 
   if (setup->rasterizer_discard) {
      setup->line = lp_setup_line_discard;
   } else {
      setup->line = lp_setup_line;
   }
}