mapnik/src/vertex_cache.cpp

/*****************************************************************************
 *
 * This file is part of Mapnik (c++ mapping toolkit)
 *
 * Copyright (C) 2021 Artem Pavlenko
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 *****************************************************************************/
// mapnik
#include <mapnik/util/math.hpp>
#include <mapnik/vertex_cache.hpp>
#include <mapnik/offset_converter.hpp>
#include <memory>

namespace mapnik {

vertex_cache::vertex_cache(vertex_cache&& rhs)
    : current_position_(std::move(rhs.current_position_))
    , segment_starting_point_(std::move(rhs.segment_starting_point_))
    , subpaths_(std::move(rhs.subpaths_))
    , position_in_segment_(std::move(rhs.position_in_segment_))
    , angle_(std::move(rhs.angle_))
    , angle_valid_(std::move(rhs.angle_valid_))
    , offseted_lines_(std::move(rhs.offseted_lines_))
    , position_(std::move(rhs.position_))
{
    // The C++11 standard doesn't guarantee iterators are valid when container is moved.
    // We can create them from indexes but we don't need to. Just let them uninitialized.
    initialized_ = false;
}

double vertex_cache::current_segment_angle()
{
    return std::atan2(current_segment_->pos.y - segment_starting_point_.y,
                      current_segment_->pos.x - segment_starting_point_.x);
}

double vertex_cache::angle(double width)
{
    double tmp = width + position_in_segment_;
    if ((tmp <= current_segment_->length) && (tmp >= 0))
    {
        // Only calculate angle on request as it is expensive
        if (!angle_valid_)
        {
            angle_ = current_segment_angle();
        }
    }
    else
    {
        scoped_state s(*this);
        if (move(width))
        {
            pixel_position const& old_pos = s.get_state().position();
            return std::atan2(current_position_.y - old_pos.y, current_position_.x - old_pos.x);
        }
        else
        {
            s.restore();
            angle_ = current_segment_angle();
        }
    }
    return width >= 0 ? angle_ : angle_ + util::pi;
}

bool vertex_cache::next_subpath()
{
    if (!initialized_)
    {
        current_subpath_ = subpaths_.begin();
        initialized_ = true;
    }
    else
    {
        current_subpath_++;
    }
    if (current_subpath_ == subpaths_.end())
        return false;
    rewind_subpath(); // Initialize position values
    return true;
}

void vertex_cache::rewind_subpath()
{
    current_segment_ = current_subpath_->vector.begin();
    // All subpaths contain at least one segment (i.e. the starting point)
    segment_starting_point_ = current_position_ = current_segment_->pos;
    position_in_segment_ = 0;
    angle_valid_ = false;
    position_ = 0;
}

void vertex_cache::reset()
{
    initialized_ = false;
}

bool vertex_cache::next_segment()
{
    segment_starting_point_ = current_segment_->pos; // Next segments starts at the end of the current one
    if (current_segment_ == current_subpath_->vector.end())
        return false;
    current_segment_++;
    angle_valid_ = false;
    if (current_segment_ == current_subpath_->vector.end())
        return false;
    return true;
}

bool vertex_cache::previous_segment()
{
    if (current_segment_ == current_subpath_->vector.begin())
        return false;
    current_segment_--;
    angle_valid_ = false;
    if (current_segment_ == current_subpath_->vector.begin())
    {
        // First segment is special
        segment_starting_point_ = current_segment_->pos;
        return true;
    }
    segment_starting_point_ = (current_segment_ - 1)->pos;
    return true;
}

vertex_cache& vertex_cache::get_offseted(double offset, double region_width)
{
    if (std::fabs(offset) < 0.01)
    {
        return *this;
    }

    offseted_lines_map::iterator pos = offseted_lines_.find(offset);
    if (pos == offseted_lines_.end())
    {
        offset_converter<vertex_cache> converter(*this);
        converter.set_offset(offset);
        pos = offseted_lines_.emplace(offset, std::make_unique<vertex_cache>(converter)).first;
    }
    vertex_cache_ptr& offseted_line = pos->second;

    offseted_line->reset();
    offseted_line->next_subpath(); // TODO: Multiple subpath support

    // find the point on the offset line closest to the current position,
    // which we'll use to make the offset line aligned to this one.
    // TODO: `position_closest_to` is disable since it is too expensive:
    // https://github.com/mapnik/mapnik/issues/2937
    // double seek = offseted_line->position_closest_to(current_position_);
    double seek = (position_ + region_width / 2.0) * offseted_line->length() / length() - region_width / 2.0;
    if (seek < 0)
        seek = 0;
    if (seek > offseted_line->length())
        seek = offseted_line->length();
    offseted_line->move(seek);

    return *offseted_line;
}

inline double dist_sq(pixel_position const& d)
{
    return d.x * d.x + d.y * d.y;
}

double vertex_cache::position_closest_to(pixel_position const& target_pos)
{
    bool first = true;
    pixel_position old_pos, new_pos;
    double lin_pos = 0.0, min_pos = 0.0, min_dist_sq = std::numeric_limits<double>::max();

    // find closest approach of each individual segment to the
    // target position. would be good if there were some kind
    // of prior, or fast test to avoid calculating on each
    // segment, but i can't think of one.
    for (segment const& seg : current_subpath_->vector)
    {
        if (first)
        {
            old_pos = seg.pos;
            min_pos = lin_pos;
            min_dist_sq = dist_sq(target_pos - old_pos);
            first = false;
        }
        else
        {
            new_pos = seg.pos;

            pixel_position d = new_pos - old_pos;
            if ((d.x != 0.0) || (d.y != 0))
            {
                pixel_position c = target_pos - old_pos;
                double t = (c.x * d.x + c.y * d.y) / dist_sq(d);

                if ((t >= 0.0) && (t <= 1.0))
                {
                    pixel_position pt = (d * t) + old_pos;
                    double pt_dist_sq = dist_sq(target_pos - pt);

                    if (pt_dist_sq < min_dist_sq)
                    {
                        min_dist_sq = pt_dist_sq;
                        min_pos = lin_pos + seg.length * t;
                    }
                }
            }

            old_pos = new_pos;
            lin_pos += seg.length;

            double end_dist_sq = dist_sq(target_pos - old_pos);
            if (end_dist_sq < min_dist_sq)
            {
                min_dist_sq = end_dist_sq;
                min_pos = lin_pos;
            }
        }
    }

    return min_pos;
}

bool vertex_cache::forward(double length)
{
    if (length < 0)
    {
        MAPNIK_LOG_ERROR(vertex_cache) << "vertex_cache::forward() called with negative argument!\n";
        return false;
    }
    return move(length);
}

bool vertex_cache::backward(double length)
{
    if (length < 0)
    {
        MAPNIK_LOG_ERROR(vertex_cache) << "vertex_cache::backward() called with negative argument!\n";
        return false;
    }
    return move(-length);
}

bool vertex_cache::move(double length)
{
    if (current_segment_ == current_subpath_->vector.end())
        return false;

    position_ += length;
    length += position_in_segment_;
    while (length >= current_segment_->length)
    {
        length -= current_segment_->length;
        if (!next_segment())
            return false; // Skip all complete segments
    }
    while (length < 0)
    {
        if (!previous_segment())
            return false;
        length += current_segment_->length;
    }
    double factor = length / current_segment_->length;
    position_in_segment_ = length;
    current_position_ = segment_starting_point_ + (current_segment_->pos - segment_starting_point_) * factor;
    return true;
}

bool vertex_cache::move_to_distance(double distance)
{
    if (current_segment_ == current_subpath_->vector.end())
        return false;

    double position_in_segment = position_in_segment_ + distance;
    if (position_in_segment < .0 || position_in_segment >= current_segment_->length)
    {
        // If there isn't enough distance left on this segment
        // then we need to search until we find the line segment that ends further than distance away
        double abs_distance = std::abs(distance);
        double new_abs_distance = .0;
        pixel_position inner_pos; // Inside circle.
        pixel_position outer_pos; // Outside circle.

        position_ -= position_in_segment_;

        if (distance > .0)
        {
            do
            {
                position_ += current_segment_->length;
                if (!next_segment())
                    return false;
                new_abs_distance = (current_position_ - current_segment_->pos).length();
            } while (new_abs_distance < abs_distance);

            inner_pos = segment_starting_point_;
            outer_pos = current_segment_->pos;
        }
        else
        {
            do
            {
                if (!previous_segment())
                    return false;
                position_ -= current_segment_->length;
                new_abs_distance = (current_position_ - segment_starting_point_).length();
            } while (new_abs_distance < abs_distance);

            inner_pos = current_segment_->pos;
            outer_pos = segment_starting_point_;
        }

        find_line_circle_intersection(current_position_.x,
                                      current_position_.y,
                                      abs_distance,
                                      inner_pos.x,
                                      inner_pos.y,
                                      outer_pos.x,
                                      outer_pos.y,
                                      current_position_.x,
                                      current_position_.y);

        position_in_segment_ = (current_position_ - segment_starting_point_).length();
        position_ += position_in_segment_;
    }
    else
    {
        position_ += distance;
        distance += position_in_segment_;
        double factor = distance / current_segment_->length;
        position_in_segment_ = distance;
        current_position_ = segment_starting_point_ + (current_segment_->pos - segment_starting_point_) * factor;
    }
    return true;
}

void vertex_cache::rewind(unsigned)
{
    vertex_subpath_ = subpaths_.begin();
    vertex_segment_ = vertex_subpath_->vector.begin();
}

unsigned vertex_cache::vertex(double* x, double* y)
{
    if (vertex_segment_ == vertex_subpath_->vector.end())
    {
        vertex_subpath_++;
        if (vertex_subpath_ == subpaths_.end())
            return agg::path_cmd_stop;
        vertex_segment_ = vertex_subpath_->vector.begin();
    }
    *x = vertex_segment_->pos.x;
    *y = vertex_segment_->pos.y;
    unsigned cmd = (vertex_segment_ == vertex_subpath_->vector.begin()) ? agg::path_cmd_move_to : agg::path_cmd_line_to;
    vertex_segment_++;
    return cmd;
}

vertex_cache::state vertex_cache::save_state() const
{
    state s;
    s.current_segment = current_segment_;
    s.position_in_segment = position_in_segment_;
    s.current_position = current_position_;
    s.segment_starting_point = segment_starting_point_;
    s.position_ = position_;
    return s;
}

void vertex_cache::restore_state(state const& s)
{
    current_segment_ = s.current_segment;
    position_in_segment_ = s.position_in_segment;
    current_position_ = s.current_position;
    segment_starting_point_ = s.segment_starting_point;
    position_ = s.position_;
    angle_valid_ = false;
}

void vertex_cache::find_line_circle_intersection(double cx,
                                                 double cy,
                                                 double radius,
                                                 double x1,
                                                 double y1,
                                                 double x2,
                                                 double y2,
                                                 double& ix,
                                                 double& iy) const
{
    double dx = x2 - x1;
    double dy = y2 - y1;

    double A = dx * dx + dy * dy;
    double B = 2 * (dx * (x1 - cx) + dy * (y1 - cy));
    double C = (x1 - cx) * (x1 - cx) + (y1 - cy) * (y1 - cy) - radius * radius;

    double det = B * B - 4 * A * C;
    if (A <= 1.0e-7 || det < 0)
    {
        // Should never happen.
        // No real solutions.
        return;
    }
    else if (det == 0)
    {
        // Could potentially happen....
        // One solution.
        double t = -B / (2 * A);
        ix = x1 + t * dx;
        iy = y1 + t * dy;
        return;
    }
    else
    {
        // Two solutions.

        // Always use the 1st one
        // We only really have one solution here, as we know the line segment will start in the circle and end outside
        double t = (-B + std::sqrt(det)) / (2 * A);
        ix = x1 + t * dx;
        iy = y1 + t * dy;

        // t = (-B - std::sqrt(det)) / (2 * A);
        // ix = x1 + t * dx;
        // iy = y1 + t * dy;

        return;
    }
}

} // namespace mapnik