quadratic function – parabola graphing 5/8 [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 15 Shape Graphing Drill 6
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

Output:

//  Philipp Siedler
//  Bjarne Stroustrup's PP
//  Chapter 15 Shape Graphing Drill 6

#define _USE_MATH_DEFINES
#include "Simple_window.h"
#include "Graph.h"
#include <cmath>

using namespace Graph_lib;

constexpr int xmax = 600;
constexpr int ymax = 600;

constexpr int x_orig = xmax / 2;
constexpr int y_orig = ymax / 2;
Point orig(x_orig, y_orig);

constexpr int r_min = -10;
constexpr int r_max = 10;

constexpr int n_points = 400;

constexpr int x_scale = 20;
constexpr int y_scale = 20;

// layout
constexpr int xoffset = 100;
constexpr int yoffset = 100;

constexpr int xspace = 100;
constexpr int yspace = 100;

constexpr int xlength = xmax - xoffset - xspace;
constexpr int ylength = ymax - yoffset - yspace;

double one(double x) { return 1; }
double slope(double x) { return x / 2; }
double square(double x) { return pow(x, 2); }

int main()
try
{
	Point tl(100, 100);
	Simple_window win(tl, xmax, ymax, "Function graphs.");

	Axis x(Axis::x, Point(orig.x - 200, orig.y), 400, 20, "1 == 20");
	x.set_color(Color::red);

	Axis y(Axis::y, Point(orig.x, orig.y + 200), 400, 20, "1 == 20");
	y.set_color(Color::red);

	Function f1(square, r_min, r_max, orig, n_points, x_scale, y_scale);
	f1.set_color(Color::black);

	Text f1_label(Point(xoffset, orig.y + 40), "pow(x,2)");

	win.attach(f1);
	win.attach(f1_label);

	win.attach(x);
	win.attach(y);

	win.wait_for_button();
}
catch (exception& e) {
	cout << e.what() << endl;
	return 1;
}
catch (...) {
	cout << "Exiting" << endl;
	return 2;
}

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