polygon/main_path.cpp

#include <iostream>
#include <string>
#include <vector>
#include <utility>

#include <math.h>

using namespace std;

struct Point
{
	double x;
	double y;

	Point& operator/=(const double& val)
	{
		x /= val;
		y /= val;
		return *this;
	}
};

Point operator-(const Point& p1, const Point& p2)
{
	return Point{.x = p1.x - p2.x, .y = p1.y - p2.y};
}

Point operator+(const Point& p1, const Point& p2)
{
	return Point{.x = p1.x + p2.x, .y = p1.y + p2.y};
}

double radians(double degrees)
{
	return degrees * M_PI / 180.0;
}

double degrees(double radians)
{
	return radians * 180.0 / M_PI;
}

Point& vec_normalize(Point& vec)
{
	double len = sqrt(vec.x * vec.x + vec.y * vec.y);
	vec /= len;
	return vec;
}

double get_angle(Point start, Point end)
{
	double angle;
	Point vec;
	double dot;

	vec = end - start;
	vec_normalize(vec);

	angle = degrees(acos(vec.x));

	if (vec.y < 0)
	{
		angle = 360 - angle;
	}

	return angle;
}

double get_stroke_angle(double prev_angle, double curr_angle)
{
	double angle;

	angle = (curr_angle - prev_angle) / 2 + prev_angle + 90;

	return angle;
}

pair<Point, Point> perform_stroke(double stroke_size, double stroke_angle, Point point)
{
	pair<Point, Point> result;
	Point add;

	add.x = cos(radians(stroke_angle)) * stroke_size / 2;
	add.y = sin(radians(stroke_angle)) * stroke_size / 2;

	result.first = point + add;
	result.second = point - add;

	return result;
}

pair<Point, Point> perform_stroke(double stroke_size, double prev_angle, double curr_angle, Point point)
{
	pair<Point, Point> result;
	Point add;
	double stroke_angle;
	double extra_angle;

	extra_angle = (curr_angle - prev_angle) / 2 + 90.0;
	stroke_angle = extra_angle + prev_angle;

	add.x = cos(radians(stroke_angle)) * stroke_size / 2 / sin(radians(extra_angle));
	add.y = sin(radians(stroke_angle)) * stroke_size / 2 / sin(radians(extra_angle));

	result.first = point + add;
	result.second = point - add;

	return result;
}

void usage(const string& name)
{
	cout << "Usage: " << name << " <stroke size> <x1> <y1> <x2> <y2> [<xN> <yN> ...]" << endl;
	cout << "\tstroke size - how big the stroke should be" << endl;
	cout << "\tx1 - x coordinate of first point" << endl;
	cout << "\ty1 - y coordinate of first point" << endl;
}

void get_polygon(double stroke_size, const vector<Point>& points)
{
	double prev_angle;
	double curr_angle;
	vector<Point> forward;
	vector<Point> backward;
	pair<Point, Point> tmp;

	for (int i = 1; i < points.size(); ++i)
	{
		prev_angle = curr_angle;
		curr_angle = get_angle(points[i - 1], points[i]);

		if (1 == i)
		{
			// First angle is end cap
			tmp = perform_stroke(stroke_size, curr_angle + 90, points[i - 1]);
		}
		else
		{
			tmp = perform_stroke(stroke_size, prev_angle, curr_angle, points[i - 1]);
		}

		forward.push_back(tmp.first);
		backward.push_back(tmp.second);
	}

	// Last angle is end cap
	tmp = perform_stroke(stroke_size, curr_angle + 90, points[points.size() - 1]);
	forward.push_back(tmp.first);
	backward.push_back(tmp.second);

	for (int i = 0; i < forward.size(); ++i)
	{
		cout << forward[i].x << "," << forward[i].y << " ";
	}

	for (int i = backward.size() - 1; i >= 0; --i)
	{
		cout << backward[i].x << "," << backward[i].y << " ";
	}

	cout << endl;
}

int main(int argc, char **argv)
{
	double stroke_size;
	Point tmp;
	vector<Point> points;
	int last_idx;

	if (argc < 5)
	{
		usage(argv[0]);
		cout << "Insufficient arguments" << endl;
		return -1;
	}

	stroke_size = stod(argv[1]);

	last_idx = argc;
	if (0 != last_idx % 2)
	{
		--last_idx;
	}

	for (int i = 2; i < last_idx; i += 2)
	{
		tmp.x = stod(argv[i]);
		tmp.y = stod(argv[i + 1]);
		points.push_back(tmp);
	}

	get_polygon(stroke_size, points);

	return 0;
}