First working implementation

modules/Whirling/Whirling.cpp

@@ -8,31 +8,126 @@
 
 #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() = default;
+        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() {
-    // adjust state for next render
-
+    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() {
-    // render one frame based on current state
-
+    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);
 }