filling a polyline with stripes [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 14 Exercise 7
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

Output:

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 14 Exercise 7

#define _USE_MATH_DEFINES
#include "Simple_window.h"
#include "Graph.h"
#include <cmath>
using namespace Graph_lib;

Point operator+(Point& p1, Point& p2) {
Point p3 = Point(p1.x + p2.x, p1.y + p2.y);
return p3;
}

Point operator-(Point& p1, Point& p2) {
Point p3 = Point(p1.x – p2.x, p1.y – p2.y);
return p3;
}

ostream& operator<<(ostream& out, Point& a) {
out << "(" << a.x << "," << a.y << ")";
return out;
}

class Striped_closed_polyline : public Closed_polyline
{
public:
Striped_closed_polyline(vector<Point> pts)
:points(pts)
{
for (int i = 0; i < pts.size(); i++) {
Closed_polyline::add(pts[i]);
}

points.push_back(pts[0]);
Closed_polyline::set_color(Color::red);
set_fill_color();
}

void set_fill_color();
void draw_lines() const;

vector<Point> inters;
vector<Mark> marks;
Lines pattern;

private:
Point a;
int r;

vector<Point> points;
};

void Striped_closed_polyline::set_fill_color()
{
Point ymax = points[0];
Point ymin = points[0];

for (int i = 0; i < points.size(); i++) {
if (points[i].y > ymax.y) {
ymax = points[i];
}
if (points[i].y < ymin.y) {
ymin = points[i];
}
}

int delta = ymax.y – ymin.y;
int step_size = 5;

for (int i = 0; i < points.size() – 1; i++) {
int counter = 0;
for (int j = 0; j < delta; j += step_size) {
if (points[i].y <= j + ymin.y && points[i + 1].y >= j + ymin.y) {

Point temp = points[i + 1] – points[i];

double slope = (double)temp.y / (double)temp.x;

int x = (double)counter / slope;

inters.push_back(Point(x + points[i].x, ymin.y + j));
counter += step_size;
}
else if (points[i + 1].y <= j + ymin.y && points[i].y >= j + ymin.y) {

Point temp = points[i] – points[i + 1];

double slope = (double)temp.y / (double)temp.x;

int x = (double)counter / slope;

inters.push_back(Point(x + points[i + 1].x, ymin.y + j));
counter += step_size;
}
}
}

// insertion_sort according to y
int i, j;
for (i = 1; i < inters.size(); i++) {
j = i;
while ((j>0) && (inters[j].y < inters[j – 1].y)) {
swap(inters[j], inters[j – 1]);
j = j – 1;
}
}

for (int i = 0; i < inters.size() – 1; i++) {
if (inters[i].y == inters[i + 1].y) {
pattern.add(inters[i], inters[i + 1]);
}
}

pattern.set_color(Color::blue);
}

void Striped_closed_polyline::draw_lines() const
{
for (int i = 0; i < inters.size(); i++) {
Mark myMark(inters[i], ‘x’);
myMark.draw();
}

pattern.draw();
Closed_polyline::draw_lines();
}

int main()
try
{
Point tl(100, 100);
Simple_window win(tl, 720, 400, "Simple Window");
Point center(win.x_max() / 2, win.y_max() / 2);

vector<Point> pts;
pts.push_back(Point(100, 100));
pts.push_back(Point(70, 150));
pts.push_back(Point(200, 300));
pts.push_back(Point(400, 120));

Striped_closed_polyline scp(pts);

win.attach(scp);
win.wait_for_button();
}
catch (exception& e) {
cout << e.what() << endl;
return 1;
}
catch (…) {
cout << "Exiting" << endl;
return 2;
}
[/code]