}
+/* from Rick Campbell <rick@campbellcentral.org> */
+static void
+spiral (Display *display, Window window, GC context,
+ int width, int height, int delay, int granularity)
+{
+# define SPIRAL_ERASE_PI_2 (M_PI + M_PI)
+# define SPIRAL_ERASE_LOOP_COUNT (10)
+# define SPIRAL_ERASE_ARC_COUNT (360.0)
+# define SPIRAL_ERASE_ANGLE_INCREMENT (SPIRAL_ERASE_PI_2 / \
+SPIRAL_ERASE_ARC_COUNT)
+# define SPIRAL_ERASE_DELAY (0)
+
+ double angle;
+ int arc_limit;
+ int arc_max_limit;
+ int length_step;
+ XPoint points [3];
+
+ angle = 0.0;
+ arc_limit = 1;
+ arc_max_limit = (int) (ceil (sqrt ((width * width) + (height * height)))
+ / 2.0);
+ length_step = ((arc_max_limit + SPIRAL_ERASE_LOOP_COUNT - 1) /
+ SPIRAL_ERASE_LOOP_COUNT);
+ arc_max_limit += length_step;
+ points [0].x = width / 2;
+ points [0].y = height / 2;
+ points [1].x = points [0].x + length_step;
+ points [1].y = points [0].y;
+ points [2].x = points [1].x;
+ points [2].y = points [1].y;
+
+ for (arc_limit = length_step;
+ arc_limit < arc_max_limit;
+ arc_limit += length_step)
+ {
+ int arc_length = length_step;
+ int length_base = arc_limit;
+ for (angle = 0.0; angle < SPIRAL_ERASE_PI_2;
+ angle += SPIRAL_ERASE_ANGLE_INCREMENT)
+ {
+ arc_length = length_base + ((length_step * angle) /
+ SPIRAL_ERASE_PI_2);
+ points [1].x = points [2].x;
+ points [1].y = points [2].y;
+ points [2].x = points [0].x + (int)(cos (angle) * arc_length);
+ points [2].y = points [0].y + (int)(sin (angle) * arc_length);
+ XFillPolygon (display, window, context, points, 3, Convex,
+ CoordModeOrigin);
+# if (SPIRAL_ERASE_DELAY != 0)
+ usleep (SPIRAL_ERASE_DELAY);
+# endif /* (SPIRAL_ERASE_DELAY != 0) */
+ }
+ }
+# undef SPIRAL_ERASE_DELAY
+# undef SPIRAL_ERASE_ANGLE_INCREMENT
+# undef SPIRAL_ERASE_ARC_COUNT
+# undef SPIRAL_ERASE_LOOP_COUNT
+# undef SPIRAL_ERASE_PI_2
+}
+
+
#undef MAX
#undef MIN
#define MAX(a,b) ((a)>(b)?(a):(b))
free(squares);
}
+/* I first saw something like this, albeit in reverse, in an early Tetris
+ implementation for the Mac.
+ -- Torbjörn Andersson <torbjorn@dev.eurotime.se>
+ */
+
+static void
+slide_lines (Display * dpy, Window window, GC gc, int width, int height,
+ int delay, int granularity)
+{
+ int slide_old_x, slide_new_x, clear_x;
+ int x, y, dx, dy;
+
+ /* This might need some tuning. The idea is to get sensible values no
+ matter what the size of the window.
+
+ Everything moves at constant speed. Should it accelerate instead? */
+
+ granularity *= 2;
+
+ dy = MAX (1, height / granularity);
+ dx = MAX (1, width / 100);
+
+ for (x = 0; x < width; x += dx)
+ {
+ for (y = 0; y < height; y += dy)
+ {
+ if ((y / dy) & 1)
+ {
+ slide_old_x = x;
+ slide_new_x = x + dx;
+ clear_x = x;
+ }
+ else
+ {
+ slide_old_x = dx;
+ slide_new_x = 0;
+ clear_x = width - x - dx;
+ }
+
+ XCopyArea (dpy, window, window, gc, slide_old_x, y, width - x - dx,
+ dy, slide_new_x, y);
+ XClearArea (dpy, window, clear_x, y, dx, dy, False);
+ }
+
+ XSync(dpy, False);
+ usleep(delay * 3);
+ }
+}
static Eraser erasers[] = {
random_lines,
squaretate,
fizzle,
random_squares,
+ spiral,
+ slide_lines,
};