1 /* epicycle --- The motion of a body with epicycles, as in the pre-Copernican
4 * Copyright (c) 1998 James Youngman <jay@gnu.org>
6 * Permission to use, copy, modify, distribute, and sell this software and its
7 * documentation for any purpose is hereby granted without fee, provided that
8 * the above copyright notice appear in all copies and that both that
9 * copyright notice and this permission notice appear in supporting
10 * documentation. No representations are made about the suitability of this
11 * software for any purpose. It is provided "as is" without express or
15 /* Standard C headers; screenhack.h assumes that these have already
16 * been included if required -- for example, it defines M_PI if not
23 #include "screenhack.h"
26 /* MIT-SHM headers omitted; this screenhack doesn't use it */
30 /*********************************************************/
31 /******************** MAGIC CONSTANTS ********************/
32 /*********************************************************/
33 #define MIN_RADIUS (5) /* smallest allowable circle radius */
34 #define FILL_PROPORTION (0.9) /* proportion of screen to fill by scaling. */
35 /*********************************************************/
36 /***************** END OF MAGIC CONSTANTS ****************/
37 /*********************************************************/
41 #define FULLCIRCLE (2.0 * M_PI) /* radians in a circle. */
44 /* Some of these resource values here are hand-tuned to give a
45 * pleasing variety of interesting shapes. These are not the only
46 * good settings, but you may find you need to change some as a group
47 * to get pleasing figures.
49 static const char *epicycle_defaults [] = {
63 "*timestepCoarseFactor: 1.0", /* no option for this resource. */
64 "*divisorPoisson: 0.4",
65 "*sizeFactorMin: 1.05",
66 "*sizeFactorMax: 2.05",
70 /* options passed to this program */
71 static XrmOptionDescRec epicycle_options [] = {
72 { "-color0", ".color0", XrmoptionSepArg, 0 },
73 { "-colors", ".colors", XrmoptionSepArg, 0 },
74 { "-colours", ".colors", XrmoptionSepArg, 0 },
75 { "-foreground", ".foreground", XrmoptionSepArg, 0 },
76 { "-delay", ".delay", XrmoptionSepArg, 0 },
77 { "-holdtime", ".holdtime", XrmoptionSepArg, 0 },
78 { "-linewidth", ".lineWidth", XrmoptionSepArg, 0 },
79 { "-min_circles", ".minCircles", XrmoptionSepArg, 0 },
80 { "-max_circles", ".maxCircles", XrmoptionSepArg, 0 },
81 { "-min_speed", ".minSpeed", XrmoptionSepArg, 0 },
82 { "-max_speed", ".maxSpeed", XrmoptionSepArg, 0 },
83 { "-harmonics", ".harmonics", XrmoptionSepArg, 0 },
84 { "-timestep", ".timestep", XrmoptionSepArg, 0 },
85 { "-divisor_poisson",".divisorPoisson",XrmoptionSepArg, 0 },
86 { "-size_factor_min", ".sizeFactorMin", XrmoptionSepArg, 0 },
87 { "-size_factor_max", ".sizeFactorMax", XrmoptionSepArg, 0 },
92 /* Each circle is centred on a point on the rim of another circle.
96 long radius; /* in pixels */
97 double w; /* position (radians ccw from x-axis) */
98 double initial_w; /* starting position */
99 double wdot; /* rotation rate (change in w per iteration) */
102 struct tagCircle *pchild;
104 typedef struct tagCircle Circle;
107 struct tagBody /* a body that moves on a system of circles. */
109 int x_origin, y_origin;
112 int current_color; /* pixel index into colors[] */
113 Circle *epicycles; /* system of circles on which it moves. */
114 struct tagBody *next; /* next in list. */
116 typedef struct tagBody Body;
124 int x_offset, y_offset;
132 int color_shift_pos; /* how far we are towards that. */
133 double colour_cycle_rate;
135 double divisorPoisson;
136 double sizeFactorMin;
137 double sizeFactorMax;
144 double T, timestep, circle, timestep_coarse;
148 int xmax, xmin, ymax, ymin;
151 eraser_state *eraser;
156 /* Determine the GCD of two numbers using Euclid's method. The other
157 * possible algorighm is Stein's method, but it's probably only going
158 * to be much faster on machines with no divide instruction, like the
159 * ARM and the Z80. The former is very fast anyway and the latter
160 * probably won't run X clients; in any case, this calculation is not
161 * the bulk of the computational expense of the program. I originally
162 * tried using Stein's method, but I wanted to remove the gotos. Not
163 * wanting to introduce possible bugs, I plumped for Euclid's method
164 * instead. Lastly, Euclid's algorithm is preferred to the
165 * generalisation for N inputs.
167 * See Knuth, section 4.5.2.
170 gcd(int u, int v) /* Euclid's Method */
172 /* If either operand of % is negative, the sign of the result is
173 * implementation-defined. See section 6.3.5 "Multiplicative
174 * Operators" of the ANSI C Standard (page 46 [LEFT HAND PAGE!] of
175 * "Annotated C Standard", Osborne, ISBN 0-07-881952-0).
190 /* Determine the Lowest Common Multiple of two integers, using
191 * Euclid's Proposition 34, as explained in Knuth's The Art of
192 * Computer Programming, Vol 2, section 4.5.2.
197 return u / gcd(u,v) * v;
201 random_radius(struct state *st, double scale)
205 r = frand(scale) * st->unit_pixels/2; /* for frand() see utils/yarandom.h */
213 random_divisor(struct state *st)
218 while (frand(1.0) < st->divisorPoisson && divisor <= st->harmonics)
222 sign = (frand(1.0) < 0.5) ? +1 : -1;
223 return sign * divisor;
228 oom(struct state *st)
230 fprintf(stderr, "Failed to allocate memory!\n");
235 /* Construct a circle or die.
238 new_circle(struct state *st, double scale)
240 Circle *p = malloc(sizeof(Circle));
242 p->radius = random_radius(st, scale);
243 p->w = p->initial_w = 0.0;
244 p->divisor = random_divisor(st);
245 p->wdot = st->wdot_max / p->divisor;
251 static void delete_circle(Circle *p)
257 delete_circle_chain(Circle *p)
261 Circle *q = p->pchild;
268 new_circle_chain(struct state *st)
271 double scale = 1.0, factor;
274 /* Parent circles are larger than their children by a factor of at
275 * least FACTOR_MIN and at most FACTOR_MAX.
277 factor = st->sizeFactorMin + frand(st->sizeFactorMax - st->sizeFactorMin);
279 /* There are between minCircles and maxCircles in each figure.
281 if (st->maxCircles == st->minCircles)
282 n = st->minCircles; /* Avoid division by zero. */
284 n = st->minCircles + random() % (st->maxCircles - st->minCircles);
289 Circle *p = new_circle(st, scale);
299 assign_random_common_w(Circle *p)
301 double w_common = frand(FULLCIRCLE); /* anywhere on the circle */
304 p->initial_w = w_common;
310 new_body(struct state *st)
312 Body *p = malloc(sizeof(Body));
315 p->epicycles = new_circle_chain(st);
316 p->current_color = 0; /* ?? start them all on different colors? */
319 p->old_x = p->old_y = 0;
320 p->x_origin = p->y_origin = 0;
322 /* Start all the epicycles at the same w value to make it easier to
323 * figure out at what T value the cycle is closed. We don't just fix
324 * the initial W value because that makes all the patterns tend to
325 * be symmetrical about the X axis.
327 assign_random_common_w(p->epicycles);
334 delete_circle_chain(p->epicycles);
340 draw_body(struct state *st, Body *pb, GC gc)
342 XDrawLine(st->dpy, st->window, gc, pb->old_x, pb->old_y, pb->x, pb->y);
346 compute_divisor_lcm(Circle *p)
352 l = lcm(l, p->divisor);
361 * Calculate the position for the body at time T. We work in double
362 * rather than int to avoid the cumulative errors that would be caused
363 * by the rounding implicit in an assignment to int.
366 move_body(Body *pb, double t)
377 for (p=pb->epicycles; NULL != p; p=p->pchild)
379 /* angular pos = initial_pos + time * angular speed */
380 /* but this is an angular position, so modulo FULLCIRCLE. */
381 p->w = fmod(p->initial_w + (t * p->wdot), FULLCIRCLE);
383 x += (p->radius * cos(p->w));
384 y += (p->radius * sin(p->w));
392 colour_init(struct state *st, XWindowAttributes *pxgwa)
397 int H = random() % 360; /* colour choice from attraction.c. */
400 double V = frand(0.25) + 0.75;
405 unsigned long valuemask = 0L;
408 /* Free any already allocated colors...
412 free_colors(st->dpy, st->cmap, st->colors, st->ncolors);
417 st->ncolors = get_integer_resource (st->dpy, "colors", "Colors");
418 if (0 == st->ncolors) /* English spelling? */
419 st->ncolors = get_integer_resource (st->dpy, "colours", "Colors");
423 if (st->ncolors <= 2)
429 st->colors = (XColor *) malloc(sizeof(*st->colors) * (st->ncolors+1));
433 make_smooth_colormap (st->dpy, pxgwa->visual, st->cmap, st->colors, &st->ncolors,
435 False, /* not writable */
436 True); /* verbose (complain about failure) */
437 if (st->ncolors <= 2)
447 st->bg = get_pixel_resource (st->dpy, st->cmap, "background", "Background");
449 /* Set the line width
451 gcv.line_width = get_integer_resource (st->dpy, "lineWidth", "Integer");
454 valuemask |= GCLineWidth;
456 gcv.join_style = JoinRound;
457 gcv.cap_style = CapRound;
459 valuemask |= (GCCapStyle | GCJoinStyle);
463 /* Set the drawing function.
465 gcv.function = GXcopy;
466 valuemask |= GCFunction;
468 /* Set the foreground.
471 fg = get_pixel_resource (st->dpy, st->cmap, "foreground", "Foreground");
474 fg = st->bg ^ get_pixel_resource (st->dpy, st->cmap, ("color0"), "Foreground");
477 valuemask |= GCForeground;
479 /* Actually create the GC.
481 st->color0 = XCreateGC (st->dpy, st->window, valuemask, &gcv);
490 setup(struct state *st)
492 XWindowAttributes xgwa;
494 XGetWindowAttributes (st->dpy, st->window, &xgwa);
495 st->cmap = xgwa.colormap;
497 st->width = xgwa.width;
498 st->height = xgwa.height;
499 st->x_offset = st->width / 2;
500 st->y_offset = st->height / 2;
501 st->unit_pixels = st->width < st->height ? st->width : st->height;
506 colour_init(st, &xgwa);
514 color_step(struct state *st, Body *pb, double frac)
518 int newshift = st->ncolors * fmod(frac * st->colour_cycle_rate, 1.0);
519 if (newshift != st->color_shift_pos)
521 pb->current_color = newshift;
522 XSetForeground (st->dpy, st->color0, st->colors[pb->current_color].pixel);
523 st->color_shift_pos = newshift;
531 distance(long x1, long y1, long x2, long y2)
537 return dx*dx + dy*dy;
540 static int poisson_irand(double p)
543 while (fabs(frand(1.0)) < p)
545 return r < 1 ? 1 : r;
550 precalculate_figure(Body *pb,
551 double this_xtime, double step,
552 int *x_max, int *y_max,
553 int *x_min, int *y_min)
557 move_body(pb, 0.0); /* move once to avoid initial line from origin */
558 *x_min = *x_max = pb->x;
559 *y_min = *y_max = pb->y;
561 for (t=0.0; t<this_xtime; t += step)
563 move_body(pb, t); /* move once to avoid initial line from origin */
575 static int i_max(int a, int b)
577 return (a>b) ? a : b;
580 static void rescale_circles(struct state *st, Body *pb,
581 int x_max, int y_max,
582 int x_min, int y_min)
584 double xscale, yscale, scale;
587 x_max -= st->x_offset;
588 x_min -= st->x_offset;
589 y_max -= st->y_offset;
590 y_min -= st->y_offset;
592 x_max = i_max(x_max, -x_min);
593 y_max = i_max(y_max, -y_min);
596 xm = st->width / 2.0;
597 ym = st->height / 2.0;
607 if (xscale < yscale) /* wider than tall */
608 scale = xscale; /* ensure width fits onscreen */
610 scale = yscale; /* ensure height fits onscreen */
613 scale *= FILL_PROPORTION; /* only fill FILL_PROPORTION of screen */
614 if (scale < 1.0) /* only reduce, don't enlarge. */
617 for (p=pb->epicycles; p; p=p->pchild)
624 printf("enlarge by x%.2f skipped...\n", scale);
629 /* angular speeds of the circles are harmonics of a fundamental
630 * value. That should please the Pythagoreans among you... :-)
633 random_wdot_max(struct state *st)
635 /* Maximum and minimum values for the choice of wdot_max. Possible
636 * epicycle speeds vary from wdot_max to (wdot_max * harmonics).
638 double minspeed, maxspeed;
639 minspeed = get_float_resource(st->dpy, "minSpeed", "Double");
640 maxspeed = get_float_resource(st->dpy, "maxSpeed", "Double");
641 return st->harmonics * (minspeed + FULLCIRCLE * frand(maxspeed-minspeed));
646 epicycle_init (Display *disp, Window win)
648 struct state *st = (struct state *) calloc (1, sizeof(*st));
652 st->holdtime = get_integer_resource (st->dpy, "holdtime", "Integer");
654 st->circle = FULLCIRCLE;
656 XClearWindow(st->dpy, st->window);
660 st->delay = get_integer_resource (st->dpy, "delay", "Integer");
661 st->harmonics = get_integer_resource(st->dpy, "harmonics", "Integer");
662 st->divisorPoisson = get_float_resource(st->dpy, "divisorPoisson", "Double");
664 st->timestep = get_float_resource(st->dpy, "timestep", "Double");
665 st->timestep_coarse = st->timestep *
666 get_float_resource(st->dpy, "timestepCoarseFactor", "Double");
668 st->sizeFactorMin = get_float_resource(st->dpy, "sizeFactorMin", "Double");
669 st->sizeFactorMax = get_float_resource(st->dpy, "sizeFactorMax", "Double");
671 st->minCircles = get_integer_resource (st->dpy, "minCircles", "Integer");
672 st->maxCircles = get_integer_resource (st->dpy, "maxCircles", "Integer");
674 st->xtime = 0; /* is this right? */
680 epicycle_draw (Display *dpy, Window window, void *closure)
682 struct state *st = (struct state *) closure;
683 int this_delay = st->delay;
686 st->eraser = erase_window (st->dpy, st->window, st->eraser);
695 /* Flush any outstanding events; this has the side effect of
696 * reducing the number of "false restarts"; resdtarts caused by
697 * one event (e.g. ConfigureNotify) followed by another
701 st->wdot_max = random_wdot_max(st);
705 delete_body(st->pb0);
708 st->pb0 = new_body(st);
709 st->pb0->x_origin = st->pb0->x = st->x_offset;
710 st->pb0->y_origin = st->pb0->y = st->y_offset;
714 st->eraser = erase_window (st->dpy, st->window, st->eraser);
718 precalculate_figure(st->pb0, st->xtime, st->timestep_coarse,
719 &st->xmax, &st->ymax, &st->xmin, &st->ymin);
721 rescale_circles(st, st->pb0, st->xmax, st->ymax, st->xmin, st->ymin);
723 move_body(st->pb0, 0.0); /* move once to avoid initial line from origin */
724 move_body(st->pb0, 0.0); /* move once to avoid initial line from origin */
727 st->T = 0.0; /* start at time zero. */
729 st->L = compute_divisor_lcm(st->pb0->epicycles);
731 st->colour_cycle_rate = fabs(st->L);
733 st->xtime = fabs(st->L * st->circle / st->wdot_max);
735 if (st->colors) /* (colors==NULL) if mono_p */
736 XSetForeground (st->dpy, st->color0, st->colors[st->pb0->current_color].pixel);
740 color_step(st, st->pb0, st->T/st->xtime );
741 draw_body(st, st->pb0, st->color0);
745 /* Check if the figure is complete...*/
746 if (st->T > st->xtime)
748 this_delay = st->holdtime * 1000000;
749 st->restart = 1; /* begin new figure. */
754 st->T += st->timestep;
755 move_body(st->pb0, st->T);
761 epicycle_reshape (Display *dpy, Window window, void *closure,
762 unsigned int w, unsigned int h)
764 struct state *st = (struct state *) closure;
769 epicycle_event (Display *dpy, Window window, void *closure, XEvent *e)
771 struct state *st = (struct state *) closure;
772 if (e->type == ButtonPress)
782 epicycle_free (Display *dpy, Window window, void *closure)
784 struct state *st = (struct state *) closure;
788 XSCREENSAVER_MODULE ("Epicycle", epicycle)