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