screensaver/modules/Whirling/Whirling.cpp

//
// Whirling.cpp
// Whirling
//
// Created by Bob Polis at 2021-09-05
// Copyright (c) 2021 SwiftCoder. All rights reserved.
//

#include "Whirling.hpp"
#include <libscscreensaver.hpp>
#include <vector>
#include <cmath>

struct Lissajous {
    double f[4]; // frequencies
    double p[4]; // phases
    int steps; // number of line segments
    double delta; // phase shift per frame
    RGB color;
    double alpha;
    double line_width;
    cairo_rectangle_t frame;

    Lissajous(double f0,
              double f1,
              double f2,
              double f3,
              double p0,
              double p1,
              double p2,
              double p3,
              int segments,
              double shift);

    double calc_x(double phi) const;
    double calc_y(double phi) const;
};

Lissajous::Lissajous(double f0,
                     double f1,
                     double f2,
                     double f3,
                     double p0,
                     double p1,
                     double p2,
                     double p3,
                     int segments,
                     double shift)
{
    f[0] = f0; f[1] = f1; f[2] = f2; f[3] = f3;
    p[0] = p0; p[1] = p1; p[2] = p2; p[3] = p3;
    steps = segments;
    delta = shift;
}

double Lissajous::calc_x(double phi) const {
    return sin(f[0] * phi + p[0]) * cos(f[1] * phi + p[1]);
}

double Lissajous::calc_y(double phi) const {
    return sin(f[2] * phi + p[2]) * cos(f[3] * phi + p[3]);
}

class Whirling : public ScreensaverPlugin {
    public:
        Whirling();
        ~Whirling() = default;

        int fps() const override;
        void update() override;
        void render() override;

    private:
        std::vector<Lissajous> knots;

        void render_knot(const Lissajous& knot);
};

ScreensaverPlugin* create_instance() {
    return new Whirling;
}

Whirling::Whirling() {
    knots.emplace_back(9, 7, 5, 7,
                       0, 0, 0, 0,
                       1000,
                       2 * M_PI / 360.0);
    Lissajous& knot = knots.back();
    knot.color = {1.0, 1.0, 1.0}; // white
    knot.alpha = 1.0; // opaque
    knot.line_width = 1.0;
}

int Whirling::fps() const {
    return 30;
}

void Whirling::update() {
    for (Lissajous& knot : knots) {
        for (int i = 0; i < 4; ++i) {
            knot.p[i] += knot.delta;
        }
        knot.frame.x = _r.width * 0.5;
        knot.frame.y = _r.height * 0.5;
        double sz = _r.width < _r.height ? _r.width : _r.height;
        knot.frame.width = sz * 0.45;
        knot.frame.height = sz * 0.45;
    }
}

void Whirling::render() {
    make_black();
    for (const Lissajous& knot : knots) {
        render_knot(knot);
    }
}

void Whirling::render_knot(const Lissajous& knot) {
    cairo_new_path(_c);
    cairo_move_to(_c,
                  knot.frame.width * knot.calc_x(0) + knot.frame.x,
                  knot.frame.height * knot.calc_y(0) + knot.frame.y);
    for (int step = 1; step < knot.steps; ++step) {
        double phi = step * 2 * M_PI / knot.steps;
        cairo_line_to(_c,
                      knot.frame.width * knot.calc_x(phi) + knot.frame.x,
                      knot.frame.height * knot.calc_y(phi) + knot.frame.y);
    }
    cairo_close_path(_c);
    cairo_set_source_rgba(_c, knot.color.r, knot.color.g, knot.color.b, knot.alpha);
    cairo_set_line_width(_c, knot.line_width);
    cairo_stroke(_c);
}