Function ClipAgainstEdge

editor/HRoom.cpp:824–883

Clip a polygon against one edge of another polygon Fills inbuf and maybe outbuf with new polygons, and writes any new verts to the vertices array Parameters: nv - the number of verts in the polygon to be clipped vertnums - pointer to list of vertex numbers in the polygon vertices - list of vertices referred to in vertnums v0,v1 - the edge we're clipping against normal - the surface normal of the p

//					outbuf - the new polygon created by the part of the input polygon that was
//clipped away 					onv - the number of verys in outbuf 					num_vertices - pointer to the number of verts in the vertices array
void ClipAgainstEdge(int nv, int16_t *vertnums, vertex *vertices, int *num_vertices, vector *v0, vector *v1,
                     vector *normal, int16_t *inbuf, int *inv, int16_t *outbuf, int *onv) {
  int i, prev, next, check;
  int16_t *ip = inbuf, *op = outbuf;
  vertex *curv, *prevv, *nextv;
  int inside_points = 0, outside_points = 0; // real inside/outside points, distinct from edge points

  for (i = 0, prev = nv - 1, next = 1; i < nv; i++) {

    curv = &vertices[vertnums[i]];

    // Find out where point lies
    check = CheckPointAgainstEdge(&curv->vec, v0, v1, normal);
    if (check == 0) { // Current vertex is on edge

      // Add to both inside & outside lists
      *op++ = vertnums[i];
      *ip++ = vertnums[i];
    } else if (check == -1) { // Current vertex is outside
      int check2;

      prevv = &vertices[vertnums[prev]];
      nextv = &vertices[vertnums[next]];

      // Clip edge w/ previous vertex
      check2 = CheckPointAgainstEdge(&prevv->vec, v0, v1, normal);
      if (check2 == 1) { // prev inside, so clip
        ClipEdge(normal, prevv, curv, v0, v1, &vertices[*num_vertices]);
        AddEdgeInsert(vertnums[prev], vertnums[i], *num_vertices);
        *op++ = *ip++ = (*num_vertices)++;
      }

      // Add current vertex to outside polygon
      *op++ = vertnums[i];
      outside_points++;

      // Clip edge w/ next vertex
      check2 = CheckPointAgainstEdge(&nextv->vec, v0, v1, normal);
      if (check2 == 1) { // next inside, so clip
        ClipEdge(normal, curv, nextv, v0, v1, &vertices[*num_vertices]);
        AddEdgeInsert(vertnums[i], vertnums[next], *num_vertices);
        *op++ = *ip++ = (*num_vertices)++;
      }
    } else { // Current vertex is inside
      ASSERT(check == 1);

      // Add current vertex to inside polygon
      *ip++ = vertnums[i];
      inside_points++;
    }

    prev = i;
    if (++next == nv)
      next = 0;
  }

  // Set number of verts for return.  If no real inside or outside points, then don't count edge points
  *inv = inside_points ? (ip - inbuf) : 0;