+
+ if (mouse_p)
+ {
+ x_dist = mouse_x - balls [i].x;
+ y_dist = mouse_y - balls [i].y;
+ dist2 = (x_dist * x_dist) + (y_dist * y_dist);
+ dist = sqrt (dist2);
+
+ if (dist > 0.1) /* the balls are not overlapping */
+ {
+ float new_acc = ((mouse_mass / dist2) *
+ ((dist < threshold) ? -1.0 : 1.0));
+ float new_acc_dist = new_acc / dist;
+ *dx_ret += new_acc_dist * x_dist;
+ *dy_ret += new_acc_dist * y_dist;
+ }
+ else
+ { /* the balls are overlapping; move randomly */
+ *dx_ret += (frand (10.0) - 5.0);
+ *dy_ret += (frand (10.0) - 5.0);
+ }
+ }