Make the ellipse plot more interesting by changing it to a four-secti…

…on drawing. Only three sections currently filled with ellipse patterns. TODO: fill the fourth one.

ellipse.c

@@ -1,4 +1,4 @@
-/* ellipse --- plot a true ellipse                          2011-10-08 */
+/* ellipse --- plot four patterns based on ellipses         2011-10-08 */
 /* Copyright (c) 2011 John Honniball, Froods Software Development      */
 
 #include <stdio.h>
@@ -7,18 +7,19 @@
 #include <math.h>
 #include "hpgllib.h"
 
-void ellipse_foci(const double x1, const double y1, const double x2, const double y2, const double d);
+void plot_ll(const double xc, const double yc, const double r1, const double r2);
+void plot_lr(const double xc, const double yc, const double r1, const double r2);
+void plot_ul(const double xc, const double yc, const double r1, const double r2);
+void plot_ur(const double xc, const double yc, const double r1, const double r2);
 
 
 int main(int argc, char * const argv[])
 {
    int opt;
    double xc, yc;
+   double w4, h4;
+   double r1, r2;
    double maxx, maxy;
-   double x1, y1;
-   double x2, y2;
-   const double scale = 40.0; /* 40 plotter units per mm */
-   int i;
 
    while ((opt = getopt(argc, argv, "no:p:s:t:v:")) != -1) {
       switch (opt) {
@@ -48,6 +49,77 @@ int main(int argc, char * const argv[])
    xc = maxx / 2.0;
    yc = maxy / 2.0;
 
+   h4 = maxy / 4.0;
+   w4 = maxx / 4.0;
+
+   r1 = maxx / 5.0;
+   r2 = maxy / 5.0;
+
+   /* Split page into quarters */
+   moveto(0.0, yc);
+   lineto(maxx, yc);
+   moveto(xc, 0.0);
+   lineto(xc, maxy);
+
+   /* Draw four ellipse plots */
+   plot_ll(w4, h4, r1, r2);
+   plot_lr(xc + w4, h4, r1, r2);
+   plot_ul(w4, yc + h4, r1, r2);
+   plot_ur(xc + w4, yc + h4, r1, r2);
+
+   plotend();
+
+   return (0);
+}
+
+
+void plot_ll(const double xc, const double yc, const double r1, const double r2)
+{
+   circle(xc, yc, r2);
+   ellipse(xc, yc, r1, r2, 0.0);
+   ellipse(xc, yc, r1 / 3.0, r2, 0.0);
+}
+
+
+void plot_lr(const double xc, const double yc, const double r1, const double r2)
+{
+   /* Inspired by "Japanese Optical and Geometrical Art" by
+      Hajime Ouchi, ISBN 0-486-23553-X, page 23, bottom */
+   int i;
+   const double delta = (2.0 * M_PI) / 8.0;
+   const double radius = r2 / 2.0;
+
+   for (i = 0; i < 8; i++) {
+      const double theta = delta * (double)i;
+
+      const double x = xc + (radius * cos(theta));
+      const double y = yc + (radius * sin(theta));
+
+      ellipse(x, y, r1 / 2.0, r2 / 2.0, theta);
+   }
+}
+
+
+void plot_ul(const double xc, const double yc, const double r1, const double r2)
+{
+   const double r3 = r1 / 2.0;
+   const double r4 = r2 / 2.0;
+
+   ellipse(xc, yc, r3 * sqrt(2.0), r4 * sqrt(2.0), 0.0);
+   ellipse(xc, yc, r1, r2, 0.0);
+   ellipse(xc - r3, yc, r3, r4, 0.0);
+   ellipse(xc, yc + r4, r3, r4, 0.0);
+   ellipse(xc, yc - r4, r3, r4, 0.0);
+   ellipse(xc + r3, yc, r3, r4, 0.0);
+}
+
+
+void plot_ur(const double xc, const double yc, const double r1, const double r2)
+{
+   circle(xc, yc, r2);
+#if 0
+   int i;
+
    /* Draw axes and foci */
    moveto(0.0, yc);
    lineto(maxx, yc);
@@ -69,13 +141,11 @@ int main(int argc, char * const argv[])
    /* Draw bunch of ellipses */
    for (i = 0; i < 10; i++)
       ellipse_foci(x1, y1, x2, y2, (110.0 + (10.0 * i)) * scale);
-
-   plotend();
-
-   return (0);
+#endif
 }
 
 
+
 void ellipse_foci(const double x1, const double y1, const double x2, const double y2, const double d)
 {
    const double dx = x2 - x1;