Chris@16: // Copyright 2011, Andrew Ross
Chris@16: //
Chris@16: // Use, modification and distribution are subject to the Boost Software License,
Chris@16: // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt).
Chris@16: #ifndef BOOST_POLYGON_DETAIL_SIMPLIFY_HPP
Chris@16: #define BOOST_POLYGON_DETAIL_SIMPLIFY_HPP
Chris@16: #include <vector>
Chris@16: 
Chris@16: namespace boost { namespace polygon { namespace detail { namespace simplify_detail {
Chris@16: 
Chris@16:   // Does a simplification/optimization pass on the polygon.  If a given
Chris@16:   // vertex lies within "len" of the line segment joining its neighbor
Chris@16:   // vertices, it is removed.
Chris@16:   template <typename T> //T is a model of point concept
Chris@16:   std::size_t simplify(std::vector<T>& dst, const std::vector<T>& src,
Chris@16:                        typename coordinate_traits<
Chris@16:                        typename point_traits<T>::coordinate_type
Chris@16:                        >::coordinate_distance len)
Chris@16:   {
Chris@16:     using namespace boost::polygon;
Chris@16:     typedef typename point_traits<T>::coordinate_type coordinate_type;
Chris@16:     typedef typename coordinate_traits<coordinate_type>::area_type ftype;
Chris@16:     typedef typename std::vector<T>::const_iterator iter;
Chris@16: 
Chris@16:     std::vector<T> out;
Chris@16:     out.reserve(src.size());
Chris@16:     dst = src;
Chris@16:     std::size_t final_result = 0;
Chris@16:     std::size_t orig_size = src.size();
Chris@16: 
Chris@16:     //I can't use == if T doesn't provide it, so use generic point concept compare
Chris@16:     bool closed = equivalence(src.front(), src.back());
Chris@16: 
Chris@16:     //we need to keep smoothing until we don't find points to remove
Chris@16:     //because removing points in the first iteration through the
Chris@16:     //polygon may leave it in a state where more removal is possible
Chris@16:     bool not_done = true;
Chris@16:     while(not_done) {
Chris@16:       if(dst.size() < 3) {
Chris@16:         dst.clear();
Chris@16:         return orig_size;
Chris@16:       }
Chris@16: 
Chris@16:       // Start with the second, test for the last point
Chris@16:       // explicitly, and exit after looping back around to the first.
Chris@16:       ftype len2 = ftype(len) * ftype(len);
Chris@16:       for(iter prev=dst.begin(), i=prev+1, next; /**/; i = next) {
Chris@16:         next = i+1;
Chris@16:         if(next == dst.end())
Chris@16:           next = dst.begin();
Chris@16: 
Chris@16:         // points A, B, C
Chris@16:         ftype ax = x(*prev), ay = y(*prev);
Chris@16:         ftype bx = x(*i), by = y(*i);
Chris@16:         ftype cx = x(*next), cy = y(*next);
Chris@16: 
Chris@16:         // vectors AB, BC and AC:
Chris@16:         ftype abx = bx-ax, aby = by-ay;
Chris@16:         ftype bcx = cx-bx, bcy = cy-by;
Chris@16:         ftype acx = cx-ax, acy = cy-ay;
Chris@16: 
Chris@16:         // dot products
Chris@16:         ftype ab_ab = abx*abx + aby*aby;
Chris@16:         ftype bc_bc = bcx*bcx + bcy*bcy;
Chris@16:         ftype ac_ac = acx*acx + acy*acy;
Chris@16:         ftype ab_ac = abx*acx + aby*acy;
Chris@16: 
Chris@16:         // projection of AB along AC
Chris@16:         ftype projf = ab_ac / ac_ac;
Chris@16:         ftype projx = acx * projf, projy = acy * projf;
Chris@16: 
Chris@16:         // perpendicular vector from the line AC to point B (i.e. AB - proj)
Chris@16:         ftype perpx = abx - projx, perpy = aby - projy;
Chris@16: 
Chris@16:         // Squared fractional distance of projection. FIXME: can
Chris@16:         // remove this division, the decisions below can be made with
Chris@16:         // just the sign of the quotient and a check to see if
Chris@16:         // abs(numerator) is greater than abs(divisor).
Chris@16:         ftype f2 = (projx*acx + projy*acx) / ac_ac;
Chris@16: 
Chris@16:         // Square of the relevant distance from point B:
Chris@16:         ftype dist2;
Chris@16:         if     (f2 < 0) dist2 = ab_ab;
Chris@16:         else if(f2 > 1) dist2 = bc_bc;
Chris@16:         else            dist2 = perpx*perpx + perpy*perpy;
Chris@16: 
Chris@16:         if(dist2 > len2) {
Chris@16:           prev = i; // bump prev, we didn't remove the segment
Chris@16:           out.push_back(*i);
Chris@16:         }
Chris@16: 
Chris@16:         if(i == dst.begin())
Chris@16:           break;
Chris@16:       }
Chris@16:       std::size_t result = dst.size() - out.size();
Chris@16:       if(result == 0) {
Chris@16:         not_done = false;
Chris@16:       } else {
Chris@16:         final_result += result;
Chris@16:         dst = out;
Chris@16:         out.clear();
Chris@16:       }
Chris@16:     } //end of while loop
Chris@16:     if(closed) {
Chris@16:       //if the input was closed we want the output to be closed
Chris@16:       --final_result;
Chris@16:       dst.push_back(dst.front());
Chris@16:     }
Chris@16:     return final_result;
Chris@16:   }
Chris@16: 
Chris@16: 
Chris@16: }}}}
Chris@16: 
Chris@16: #endif