git.hungrycats.org Git - xscreensaver/blob - hacks/fluidballs.c

   1 /* fluidballs, Copyright (c) 2000 by Peter Birtles <peter@bqdesign.com.au>
   2  *
   3  * Permission to use, copy, modify, distribute, and sell this software and its
   4  * documentation for any purpose is hereby granted without fee, provided that
   5  * the above copyright notice appear in all copies and that both that
   6  * copyright notice and this permission notice appear in supporting
   7  * documentation.  No representations are made about the suitability of this
   8  * software for any purpose.  It is provided "as is" without express or
   9  * implied warranty.
  10  *
  11  * Ported to X11 and xscreensaver by jwz, 27-Feb-2002.
  12  *
  13  * http://astronomy.swin.edu.au/~pbourke/modelling/fluid/
  14  *
  15  * Some physics improvements by Steven Barker <steve@blckknght.org>
  16  */
  17
  18 /* Future ideas:
  19  * Specifying a distribution in the ball sizes (with a gamma curve, possibly).
  20  * Brownian motion, for that extra touch of realism.
  21  *
  22  * It would be nice to detect when there are more balls than fit in
  23  * the window, and scale the number of balls back.  Useful for the
  24  * xscreensaver-demo preview, which is often too tight by default.
  25  */
  26
  27 #include <math.h>
  28 #include "screenhack.h"
  29 #include <stdio.h>
  30
  31 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
  32 #include "xdbe.h"
  33 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
  34
  35 typedef struct {
  36   Display *dpy;
  37   Window window;
  38   XWindowAttributes xgwa;
  39   int delay;
  40
  41   Pixmap b, ba; /* double-buffer to reduce flicker */
  42 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
  43   XdbeBackBuffer backb;
  44   Bool dbeclear_p;
  45 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
  46
  47   GC draw_gc;           /* most of the balls */
  48   GC draw_gc2;          /* the ball being dragged with the mouse */
  49   GC erase_gc;
  50   XColor fg;
  51   XColor fg2;
  52
  53   int count;            /* number of balls */
  54   float xmin, ymin;     /* rectangle of window, relative to root */
  55   float xmax, ymax;
  56
  57   int mouse_ball;       /* index of ball being dragged, or 0 if none. */
  58
  59   float tc;             /* time constant (time-warp multiplier) */
  60   float accx;           /* horizontal acceleration (wind) */
  61   float accy;           /* vertical acceleration (gravity) */
  62
  63   float *vx,  *vy;      /* current ball velocities */
  64   float *px,  *py;      /* current ball positions */
  65   float *opx, *opy;     /* previous ball positions */
  66   float *r;             /* ball radiuses */
  67
  68   float *m;             /* ball mass, precalculated */
  69   float e;              /* coeficient of elasticity */
  70   float max_radius;     /* largest radius of any ball */
  71
  72   Bool random_sizes_p;  /* Whether balls should be various sizes up to max. */
  73   Bool shake_p;         /* Whether to mess with gravity when things settle. */
  74   Bool dbuf;            /* Whether we're using double buffering. */
  75   float shake_threshold;
  76   int time_since_shake;
  77
  78   Bool fps_p;           /* Whether to draw some text at the bottom. */
  79   GC font_gc;
  80   int font_height;
  81   int font_baseline;
  82   int frame_count;
  83   int collision_count;
  84   char fps_str[1024];
  85
  86   int time_tick;
  87   struct timeval last_time;
  88
  89 } b_state;
  90
  91
  92 /* Draws the frames per second string */
  93 static void
  94 draw_fps_string (b_state *state)
  95 {
  96   XFillRectangle (state->dpy, state->b, state->erase_gc,
  97                   0, state->xgwa.height - state->font_height*3 - 20,
  98                   state->xgwa.width, state->font_height*3 + 20);
  99   XDrawImageString (state->dpy, state->b, state->font_gc,
 100                     10, state->xgwa.height - state->font_height*2 -
 101                     state->font_baseline - 10,
 102                     state->fps_str, strlen(state->fps_str));
 103 }
 104
 105 /* Finds the origin of the window relative to the root window, by
 106    walking up the window tree until it reaches the top.
 107  */
 108 static void
 109 window_origin (Display *dpy, Window window, int *x, int *y)
 110 {
 111   XTranslateCoordinates (dpy, window, RootWindow (dpy, DefaultScreen (dpy)),
 112                          0, 0, x, y, &window);
 113 }
 114
 115
 116 /* Queries the window position to see if the window has moved or resized.
 117    We poll this instead of waiting for ConfigureNotify events, because
 118    when the window manager moves the window, only one ConfigureNotify
 119    comes in: at the end of the motion.  If we poll, we can react to the
 120    new position while the window is still being moved.  (Assuming the WM
 121    does OpaqueMove, of course.)
 122  */
 123 static void
 124 check_window_moved (b_state *state)
 125 {
 126   float oxmin = state->xmin;
 127   float oxmax = state->xmax;
 128   float oymin = state->ymin;
 129   float oymax = state->ymax;
 130   int wx, wy;
 131   XGetWindowAttributes (state->dpy, state->window, &state->xgwa);
 132   window_origin (state->dpy, state->window, &wx, &wy);
 133   state->xmin = wx;
 134   state->ymin = wy;
 135   state->xmax = state->xmin + state->xgwa.width;
 136   state->ymax = state->ymin + state->xgwa.height - (state->font_height*3) -
 137     (state->font_height ? 22 : 0);
 138
 139   if (state->dbuf && (state->ba))
 140     {
 141       if (oxmax != state->xmax || oymax != state->ymax)
 142         {
 143           XFreePixmap (state->dpy, state->ba);
 144           state->ba = XCreatePixmap (state->dpy, state->window,
 145                                      state->xgwa.width, state->xgwa.height,
 146                                      state->xgwa.depth);
 147           XFillRectangle (state->dpy, state->ba, state->erase_gc, 0, 0,
 148                           state->xgwa.width, state->xgwa.height);
 149           state->b = state->ba;
 150         }
 151     }
 152   else
 153     {
 154       /* Only need to erase the window if the origin moved */
 155       if (oxmin != state->xmin || oymin != state->ymin)
 156         XClearWindow (state->dpy, state->window);
 157       else if (state->fps_p && oymax != state->ymax)
 158         XFillRectangle (state->dpy, state->b, state->erase_gc,
 159                         0, state->xgwa.height - state->font_height*3,
 160                         state->xgwa.width, state->font_height*3);
 161     }
 162 }
 163
 164
 165 /* Returns the position of the mouse relative to the root window.
 166  */
 167 static void
 168 query_mouse (b_state *state, int *x, int *y)
 169 {
 170   Window root1, child1;
 171   int mouse_x, mouse_y, root_x, root_y;
 172   unsigned int mask;
 173   if (XQueryPointer (state->dpy, state->window, &root1, &child1,
 174                      &root_x, &root_y, &mouse_x, &mouse_y, &mask))
 175     {
 176       *x = root_x;
 177       *y = root_y;
 178     }
 179   else
 180     {
 181       *x = -9999;
 182       *y = -9999;
 183     }
 184 }
 185
 186 /* Re-pick the colors of the balls, and the mouse-ball.
 187  */
 188 static void
 189 recolor (b_state *state)
 190 {
 191   if (state->fg.flags)
 192     XFreeColors (state->dpy, state->xgwa.colormap, &state->fg.pixel, 1, 0);
 193   if (state->fg2.flags)
 194     XFreeColors (state->dpy, state->xgwa.colormap, &state->fg2.pixel, 1, 0);
 195
 196   state->fg.flags  = DoRed|DoGreen|DoBlue;
 197   state->fg.red    = 0x8888 + (random() % 0x8888);
 198   state->fg.green  = 0x8888 + (random() % 0x8888);
 199   state->fg.blue   = 0x8888 + (random() % 0x8888);
 200
 201   state->fg2.flags = DoRed|DoGreen|DoBlue;
 202   state->fg2.red   = 0x8888 + (random() % 0x8888);
 203   state->fg2.green = 0x8888 + (random() % 0x8888);
 204   state->fg2.blue  = 0x8888 + (random() % 0x8888);
 205
 206   if (XAllocColor (state->dpy, state->xgwa.colormap, &state->fg))
 207     XSetForeground (state->dpy, state->draw_gc,  state->fg.pixel);
 208
 209   if (XAllocColor (state->dpy, state->xgwa.colormap, &state->fg2))
 210     XSetForeground (state->dpy, state->draw_gc2, state->fg2.pixel);
 211 }
 212
 213 /* Initialize the state structure and various X data.
 214  */
 215 static void *
 216 fluidballs_init (Display *dpy, Window window)
 217 {
 218   int i;
 219   float extx, exty;
 220   b_state *state = (b_state *) calloc (1, sizeof(*state));
 221   XGCValues gcv;
 222
 223   state->dpy = dpy;
 224   state->window = window;
 225   state->delay = get_integer_resource (dpy, "delay", "Integer");
 226
 227   check_window_moved (state);
 228
 229   state->dbuf = get_boolean_resource (dpy, "doubleBuffer", "Boolean");
 230
 231 # ifdef HAVE_COCOA      /* Don't second-guess Quartz's double-buffering */
 232   state->dbuf = False;
 233 # endif
 234
 235   if (state->dbuf)
 236     {
 237 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
 238       state->dbeclear_p = get_boolean_resource (dpy, "useDBEClear", "Boolean");
 239       if (state->dbeclear_p)
 240         state->b = xdbe_get_backbuffer (dpy, window, XdbeBackground);
 241       else
 242         state->b = xdbe_get_backbuffer (dpy, window, XdbeUndefined);
 243       state->backb = state->b;
 244 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
 245
 246       if (!state->b)
 247         {
 248           state->ba = XCreatePixmap (state->dpy, state->window,
 249                                      state->xgwa.width, state->xgwa.height,
 250                                      state->xgwa.depth);
 251           state->b = state->ba;
 252         }
 253     }
 254   else
 255     {
 256       state->b = state->window;
 257     }
 258
 259   /* Select ButtonRelease events on the external window, if no other app has
 260      already selected it (only one app can select it at a time: BadAccess. */
 261 #if 0
 262   if (! (state->xgwa.all_event_masks & ButtonReleaseMask))
 263     XSelectInput (state->dpy, state->window,
 264                   state->xgwa.your_event_mask | ButtonReleaseMask);
 265 #endif
 266
 267   gcv.foreground = get_pixel_resource(state->dpy, state->xgwa.colormap,
 268                                       "foreground", "Foreground");
 269   gcv.background = get_pixel_resource(state->dpy, state->xgwa.colormap,
 270                                       "background", "Background");
 271   state->draw_gc = XCreateGC (state->dpy, state->b,
 272                               GCForeground|GCBackground, &gcv);
 273
 274   gcv.foreground = get_pixel_resource(state->dpy, state->xgwa.colormap,
 275                                       "mouseForeground", "MouseForeground");
 276   state->draw_gc2 = XCreateGC (state->dpy, state->b,
 277                                GCForeground|GCBackground, &gcv);
 278
 279   gcv.foreground = gcv.background;
 280   state->erase_gc = XCreateGC (state->dpy, state->b,
 281                                GCForeground|GCBackground, &gcv);
 282
 283
 284   if (state->ba)
 285     XFillRectangle (state->dpy, state->ba, state->erase_gc, 0, 0,
 286                     state->xgwa.width, state->xgwa.height);
 287
 288   recolor (state);
 289
 290   extx = state->xmax - state->xmin;
 291   exty = state->ymax - state->ymin;
 292
 293   state->count = get_integer_resource (dpy, "count", "Count");
 294   if (state->count < 1) state->count = 20;
 295
 296   state->max_radius = get_float_resource (dpy, "size", "Size") / 2;
 297   if (state->max_radius < 1.0) state->max_radius = 1.0;
 298
 299   state->random_sizes_p = get_boolean_resource (dpy, "random", "Random");
 300
 301   /* If the initial window size is too small to hold all these balls,
 302      make fewer of them...
 303    */
 304   {
 305     float r = (state->random_sizes_p
 306                ? state->max_radius * 0.7
 307                : state->max_radius);
 308     float ball_area = M_PI * r * r;
 309     float balls_area = state->count * ball_area;
 310     float window_area = state->xgwa.width * state->xgwa.height;
 311     window_area *= 0.75;  /* don't pack it completely full */
 312     if (balls_area > window_area)
 313       state->count = window_area / ball_area;
 314   }
 315
 316   state->accx = get_float_resource (dpy, "wind", "Wind");
 317   if (state->accx < -1.0 || state->accx > 1.0) state->accx = 0;
 318
 319   state->accy = get_float_resource (dpy, "gravity", "Gravity");
 320   if (state->accy < -1.0 || state->accy > 1.0) state->accy = 0.01;
 321
 322   state->e = get_float_resource (dpy, "elasticity", "Elacitcity");
 323   if (state->e < 0.2 || state->e > 1.0) state->e = 0.97;
 324
 325   state->tc = get_float_resource (dpy, "timeScale", "TimeScale");
 326   if (state->tc <= 0 || state->tc > 10) state->tc = 1.0;
 327
 328   state->shake_p = get_boolean_resource (dpy, "shake", "Shake");
 329   state->shake_threshold = get_float_resource (dpy, "shakeThreshold",
 330                                                "ShakeThreshold");
 331   state->time_tick = 999999;
 332
 333 # ifdef USE_IPHONE      /* Always obey real-world gravity */
 334   state->shake_p = False;
 335 # endif
 336
 337
 338   state->fps_p = get_boolean_resource (dpy, "doFPS", "DoFPS");
 339   if (state->fps_p)
 340     {
 341       XFontStruct *font;
 342       char *fontname = get_string_resource (dpy, "fpsFont", "Font");
 343       if (!fontname) fontname = "-*-courier-bold-r-normal-*-180-*";
 344       font = XLoadQueryFont (dpy, fontname);
 345       if (!font) font = XLoadQueryFont (dpy, "fixed");
 346       if (!font) exit(-1);
 347       gcv.font = font->fid;
 348       gcv.foreground = get_pixel_resource(state->dpy, state->xgwa.colormap,
 349                                           "textColor", "Foreground");
 350       state->font_gc = XCreateGC(dpy, state->b,
 351                                  GCFont|GCForeground|GCBackground, &gcv);
 352       state->font_height = font->ascent + font->descent;
 353       state->font_baseline = font->descent;
 354     }
 355
 356   state->m   = (float *) malloc (sizeof (*state->m)   * (state->count + 1));
 357   state->r   = (float *) malloc (sizeof (*state->r)   * (state->count + 1));
 358   state->vx  = (float *) malloc (sizeof (*state->vx)  * (state->count + 1));
 359   state->vy  = (float *) malloc (sizeof (*state->vy)  * (state->count + 1));
 360   state->px  = (float *) malloc (sizeof (*state->px)  * (state->count + 1));
 361   state->py  = (float *) malloc (sizeof (*state->py)  * (state->count + 1));
 362   state->opx = (float *) malloc (sizeof (*state->opx) * (state->count + 1));
 363   state->opy = (float *) malloc (sizeof (*state->opy) * (state->count + 1));
 364
 365   for (i=1; i<=state->count; i++)
 366     {
 367       state->px[i] = frand(extx) + state->xmin;
 368       state->py[i] = frand(exty) + state->ymin;
 369       state->vx[i] = frand(0.2) - 0.1;
 370       state->vy[i] = frand(0.2) - 0.1;
 371
 372       state->r[i] = (state->random_sizes_p
 373                      ? ((0.2 + frand(0.8)) * state->max_radius)
 374                      : state->max_radius);
 375       /*state->r[i] = pow(frand(1.0), state->sizegamma) * state->max_radius;*/
 376
 377       /* state->m[i] = pow(state->r[i],2) * M_PI; */
 378       state->m[i] = pow(state->r[i],3) * M_PI * 1.3333;
 379     }
 380
 381   memcpy (state->opx, state->px, sizeof (*state->opx) * (state->count + 1));
 382   memcpy (state->opy, state->py, sizeof (*state->opx) * (state->count + 1));
 383
 384   return state;
 385 }
 386
 387
 388 /* Messes with gravity: permute "down" to be in a random direction.
 389  */
 390 static void
 391 shake (b_state *state)
 392 {
 393   float a = state->accx;
 394   float b = state->accy;
 395   int i = random() % 4;
 396
 397   switch (i)
 398     {
 399     case 0:
 400       state->accx = a;
 401       state->accy = b;
 402       break;
 403     case 1:
 404       state->accx = -a;
 405       state->accy = -b;
 406       break;
 407     case 2:
 408       state->accx = b;
 409       state->accy = a;
 410       break;
 411     case 3:
 412       state->accx = -b;
 413       state->accy = -a;
 414       break;
 415     default:
 416       abort();
 417       break;
 418     }
 419
 420   state->time_since_shake = 0;
 421   recolor (state);
 422 }
 423
 424
 425 /* Look at the current time, and update state->time_since_shake.
 426    Draw the FPS display if desired.
 427  */
 428 static void
 429 check_wall_clock (b_state *state, float max_d)
 430 {
 431   state->frame_count++;
 432
 433   if (state->time_tick++ > 20)  /* don't call gettimeofday() too often -- it's slow. */
 434     {
 435       struct timeval now;
 436 # ifdef GETTIMEOFDAY_TWO_ARGS
 437       struct timezone tzp;
 438       gettimeofday(&now, &tzp);
 439 # else
 440       gettimeofday(&now);
 441 # endif
 442
 443       if (state->last_time.tv_sec == 0)
 444         state->last_time = now;
 445
 446       state->time_tick = 0;
 447       if (now.tv_sec == state->last_time.tv_sec)
 448         return;
 449
 450       state->time_since_shake += (now.tv_sec - state->last_time.tv_sec);
 451
 452 # ifdef USE_IPHONE      /* Always obey real-world gravity */
 453       {
 454         float a = fabs (fabs(state->accx) > fabs(state->accy)
 455                         ? state->accx : state->accy);
 456         switch ((int) current_device_rotation ()) {
 457         case    0: case  360: state->accx =  0; state->accy =  a; break;
 458         case  -90:            state->accx = -a; state->accy =  0; break;
 459         case   90:            state->accx =  a; state->accy =  0; break;
 460         case  180: case -180: state->accx =  0; state->accy = -a; break;
 461         default: break;
 462         }
 463       }
 464 # endif /* USE_IPHONE */
 465
 466       if (state->fps_p)
 467         {
 468           float elapsed = ((now.tv_sec  + (now.tv_usec  / 1000000.0)) -
 469                            (state->last_time.tv_sec + (state->last_time.tv_usec / 1000000.0)));
 470           float fps = state->frame_count / elapsed;
 471           float cps = state->collision_count / elapsed;
 472
 473           sprintf (state->fps_str, "Collisions: %.3f/frame  Max motion: %.3f",
 474                    cps/fps, max_d);
 475
 476           draw_fps_string(state);
 477         }
 478
 479       state->frame_count = 0;
 480       state->collision_count = 0;
 481       state->last_time = now;
 482     }
 483 }
 484
 485 /* Erases the balls at their previous positions, and draws the new ones.
 486  */
 487 static void
 488 repaint_balls (b_state *state)
 489 {
 490   int a;
 491   int x1a, x2a, y1a, y2a;
 492   int x1b, x2b, y1b, y2b;
 493   float max_d = 0;
 494
 495 #ifdef HAVE_COCOA       /* Don't second-guess Quartz's double-buffering */
 496   XClearWindow (state->dpy, state->b);
 497 #endif
 498
 499   for (a=1; a <= state->count; a++)
 500     {
 501       GC gc;
 502       x1a = (state->opx[a] - state->r[a] - state->xmin);
 503       y1a = (state->opy[a] - state->r[a] - state->ymin);
 504       x2a = (state->opx[a] + state->r[a] - state->xmin);
 505       y2a = (state->opy[a] + state->r[a] - state->ymin);
 506
 507       x1b = (state->px[a] - state->r[a] - state->xmin);
 508       y1b = (state->py[a] - state->r[a] - state->ymin);
 509       x2b = (state->px[a] + state->r[a] - state->xmin);
 510       y2b = (state->py[a] + state->r[a] - state->ymin);
 511
 512 #ifndef HAVE_COCOA      /* Don't second-guess Quartz's double-buffering */
 513 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
 514       if (!state->dbeclear_p || !state->backb)
 515 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
 516         {
 517 /*        if (x1a != x1b || y1a != y1b)   -- leaves turds if we optimize this */
 518             {
 519               gc = state->erase_gc;
 520               XFillArc (state->dpy, state->b, gc,
 521                         x1a, y1a, x2a-x1a, y2a-y1a,
 522                         0, 360*64);
 523             }
 524         }
 525 #endif /* !HAVE_COCOA */
 526
 527       if (state->mouse_ball == a)
 528         gc = state->draw_gc2;
 529       else
 530         gc = state->draw_gc;
 531
 532       XFillArc (state->dpy, state->b, gc,
 533                 x1b, y1b, x2b-x1b, y2b-y1b,
 534                 0, 360*64);
 535
 536       if (state->shake_p)
 537         {
 538           /* distance this ball moved this frame */
 539           float d = ((state->px[a] - state->opx[a]) *
 540                      (state->px[a] - state->opx[a]) +
 541                      (state->py[a] - state->opy[a]) *
 542                      (state->py[a] - state->opy[a]));
 543           if (d > max_d) max_d = d;
 544         }
 545
 546       state->opx[a] = state->px[a];
 547       state->opy[a] = state->py[a];
 548     }
 549
 550   if (state->fps_p
 551 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
 552       && (state->backb ? state->dbeclear_p : 1)
 553 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
 554       )
 555     draw_fps_string(state);
 556
 557 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
 558   if (state->backb)
 559     {
 560       XdbeSwapInfo info[1];
 561       info[0].swap_window = state->window;
 562       info[0].swap_action = (state->dbeclear_p ? XdbeBackground : XdbeUndefined);
 563       XdbeSwapBuffers (state->dpy, info, 1);
 564     }
 565   else
 566 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
 567   if (state->dbuf)
 568     {
 569       XCopyArea (state->dpy, state->b, state->window, state->erase_gc,
 570                  0, 0, state->xgwa.width, state->xgwa.height, 0, 0);
 571     }
 572
 573   if (state->shake_p && state->time_since_shake > 5)
 574     {
 575       max_d /= state->max_radius;
 576       if (max_d < state->shake_threshold ||  /* when its stable */
 577           state->time_since_shake > 30)      /* or when 30 secs has passed */
 578         {
 579           shake (state);
 580         }
 581     }
 582
 583   check_wall_clock (state, max_d);
 584 }
 585
 586
 587 /* Implements the laws of physics: move balls to their new positions.
 588  */
 589 static void
 590 update_balls (b_state *state)
 591 {
 592   int a, b;
 593   float d, vxa, vya, vxb, vyb, dd, cdx, cdy;
 594   float ma, mb, vca, vcb, dva, dvb;
 595   float dee2;
 596
 597   check_window_moved (state);
 598
 599   /* If we're currently tracking the mouse, update that ball first.
 600    */
 601   if (state->mouse_ball != 0)
 602     {
 603       int mouse_x, mouse_y;
 604       query_mouse (state, &mouse_x, &mouse_y);
 605       state->px[state->mouse_ball] = mouse_x;
 606       state->py[state->mouse_ball] = mouse_y;
 607       state->vx[state->mouse_ball] =
 608         (0.1 *
 609          (state->px[state->mouse_ball] - state->opx[state->mouse_ball]) *
 610          state->tc);
 611       state->vy[state->mouse_ball] =
 612         (0.1 *
 613          (state->py[state->mouse_ball] - state->opy[state->mouse_ball]) *
 614          state->tc);
 615     }
 616
 617   /* For each ball, compute the influence of every other ball. */
 618   for (a=1; a <= state->count -  1; a++)
 619     for (b=a + 1; b <= state->count; b++)
 620       {
 621          d = ((state->px[a] - state->px[b]) *
 622               (state->px[a] - state->px[b]) +
 623               (state->py[a] - state->py[b]) *
 624               (state->py[a] - state->py[b]));
 625          dee2 = (state->r[a] + state->r[b]) *
 626                 (state->r[a] + state->r[b]);
 627          if (d < dee2)
 628          {
 629             state->collision_count++;
 630             d = sqrt(d);
 631             dd = state->r[a] + state->r[b] - d;
 632
 633             cdx = (state->px[b] - state->px[a]) / d;
 634             cdy = (state->py[b] - state->py[a]) / d;
 635
 636             /* Move each ball apart from the other by half the
 637              * 'collision' distance.
 638              */
 639             state->px[a] -= 0.5 * dd * cdx;
 640             state->py[a] -= 0.5 * dd * cdy;
 641             state->px[b] += 0.5 * dd * cdx;
 642             state->py[b] += 0.5 * dd * cdy;
 643
 644             ma = state->m[a];
 645             mb = state->m[b];
 646
 647             vxa = state->vx[a];
 648             vya = state->vy[a];
 649             vxb = state->vx[b];
 650             vyb = state->vy[b];
 651
 652             vca = vxa * cdx + vya * cdy; /* the component of each velocity */
 653             vcb = vxb * cdx + vyb * cdy; /* along the axis of the collision */
 654
 655             /* elastic collison */
 656             dva = (vca * (ma - mb) + vcb * 2 * mb) / (ma + mb) - vca;
 657             dvb = (vcb * (mb - ma) + vca * 2 * ma) / (ma + mb) - vcb;
 658
 659             dva *= state->e; /* some energy lost to inelasticity */
 660             dvb *= state->e;
 661
 662 #if 0
 663             dva += (frand (50) - 25) / ma;   /* q: why are elves so chaotic? */
 664             dvb += (frand (50) - 25) / mb;   /* a: brownian motion. */
 665 #endif
 666
 667             vxa += dva * cdx;
 668             vya += dva * cdy;
 669             vxb += dvb * cdx;
 670             vyb += dvb * cdy;
 671
 672             state->vx[a] = vxa;
 673             state->vy[a] = vya;
 674             state->vx[b] = vxb;
 675             state->vy[b] = vyb;
 676          }
 677       }
 678
 679    /* Force all balls to be on screen.
 680     */
 681   for (a=1; a <= state->count; a++)
 682     {
 683       if (state->px[a] <= (state->xmin + state->r[a]))
 684         {
 685           state->px[a] = state->xmin + state->r[a];
 686           state->vx[a] = -state->vx[a] * state->e;
 687         }
 688       if (state->px[a] >= (state->xmax - state->r[a]))
 689         {
 690           state->px[a] = state->xmax - state->r[a];
 691           state->vx[a] = -state->vx[a] * state->e;
 692         }
 693       if (state->py[a] <= (state->ymin + state->r[a]))
 694         {
 695           state->py[a] = state->ymin + state->r[a];
 696           state->vy[a] = -state->vy[a] * state->e;
 697         }
 698       if (state->py[a] >= (state->ymax - state->r[a]))
 699         {
 700           state->py[a] = state->ymax - state->r[a];
 701           state->vy[a] = -state->vy[a] * state->e;
 702         }
 703     }
 704
 705   /* Apply gravity to all balls.
 706    */
 707   for (a=1; a <= state->count; a++)
 708     if (a != state->mouse_ball)
 709       {
 710         state->vx[a] += state->accx * state->tc;
 711         state->vy[a] += state->accy * state->tc;
 712         state->px[a] += state->vx[a] * state->tc;
 713         state->py[a] += state->vy[a] * state->tc;
 714       }
 715 }
 716
 717
 718 /* Handle X events, specifically, allow a ball to be picked up with the mouse.
 719  */
 720 static Bool
 721 fluidballs_event (Display *dpy, Window window, void *closure, XEvent *event)
 722 {
 723   b_state *state = (b_state *) closure;
 724
 725   if (event->xany.type == ButtonPress)
 726     {
 727       int i, rx, ry;
 728       XTranslateCoordinates (dpy, window, RootWindow (dpy, DefaultScreen(dpy)),
 729                              event->xbutton.x, event->xbutton.y, &rx, &ry,
 730                              &window);
 731
 732       if (state->mouse_ball != 0)  /* second down-click?  drop the ball. */
 733         {
 734           state->mouse_ball = 0;
 735           return True;
 736         }
 737       else
 738         {
 739           /* When trying to pick up a ball, first look for a click directly
 740              inside the ball; but if we don't find it, expand the radius
 741              outward until we find something nearby.
 742            */
 743           float max = state->max_radius * 4;
 744           float step = max / 10;
 745           float r2;
 746           for (r2 = step; r2 < max; r2 += step) {
 747             for (i = 1; i <= state->count; i++)
 748               {
 749                 float d = ((state->px[i] - rx) * (state->px[i] - rx) +
 750                            (state->py[i] - ry) * (state->py[i] - ry));
 751                 float r = state->r[i];
 752                 if (r2 > r) r = r2;
 753                 if (d < r*r)
 754                   {
 755                     state->mouse_ball = i;
 756                     return True;
 757                   }
 758               }
 759           }
 760         }
 761       return True;
 762     }
 763   else if (event->xany.type == ButtonRelease)   /* drop the ball */
 764     {
 765       state->mouse_ball = 0;
 766       return True;
 767     }
 768
 769   return False;
 770 }
 771
 772 static unsigned long
 773 fluidballs_draw (Display *dpy, Window window, void *closure)
 774 {
 775   b_state *state = (b_state *) closure;
 776   repaint_balls(state);
 777   update_balls(state);
 778   return state->delay;
 779 }
 780
 781 static void
 782 fluidballs_reshape (Display *dpy, Window window, void *closure,
 783                  unsigned int w, unsigned int h)
 784 {
 785 }
 786
 787 static void
 788 fluidballs_free (Display *dpy, Window window, void *closure)
 789 {
 790   b_state *state = (b_state *) closure;
 791   free (state);
 792 }
 793
 794
 795 static const char *fluidballs_defaults [] = {
 796   ".background:         black",
 797   ".foreground:         yellow",
 798   ".textColor:          white",
 799   "*mouseForeground:    white",
 800   "*delay:              10000",
 801   "*count:              300",
 802   "*size:               25",
 803   "*random:             True",
 804   "*gravity:            0.01",
 805   "*wind:               0.00",
 806   "*elasticity:         0.97",
 807   "*timeScale:          1.0",
 808   "*shake:              True",
 809   "*shakeThreshold:     0.015",
 810   "*doubleBuffer:       True",
 811 #ifdef HAVE_DOUBLE_BUFFER_EXTENSION
 812   "*useDBE:             True",
 813   "*useDBEClear:        True",
 814 #endif /* HAVE_DOUBLE_BUFFER_EXTENSION */
 815 #ifdef USE_IPHONE
 816   "*ignoreRotation:     True",
 817 #endif
 818   0
 819 };
 820
 821 static XrmOptionDescRec fluidballs_options [] = {
 822   { "-delay",           ".delay",       XrmoptionSepArg, 0 },
 823   { "-count",           ".count",       XrmoptionSepArg, 0 },
 824   { "-size",            ".size",        XrmoptionSepArg, 0 },
 825   { "-count",           ".count",       XrmoptionSepArg, 0 },
 826   { "-gravity",         ".gravity",     XrmoptionSepArg, 0 },
 827   { "-wind",            ".wind",        XrmoptionSepArg, 0 },
 828   { "-elasticity",      ".elasticity",  XrmoptionSepArg, 0 },
 829   { "-shake",           ".shake",       XrmoptionNoArg, "True" },
 830   { "-no-shake",        ".shake",       XrmoptionNoArg, "False" },
 831   { "-random",          ".random",      XrmoptionNoArg, "True" },
 832   { "-no-random",       ".random",      XrmoptionNoArg, "False" },
 833   { "-nonrandom",       ".random",      XrmoptionNoArg, "False" },
 834   { "-db",              ".doubleBuffer", XrmoptionNoArg,  "True" },
 835   { "-no-db",           ".doubleBuffer", XrmoptionNoArg,  "False" },
 836   { 0, 0, 0, 0 }
 837 };
 838
 839
 840 XSCREENSAVER_MODULE ("FluidBalls", fluidballs)