+ return FORCE_MOVE;
+}
+
+void UnstableTile::shake (void)
+{
+ if (state != STATE_NORMAL)
+ return;
+
+ if (sprite->has_action ("shake")) {
+ state = STATE_SHAKE;
+ this->set_action ("shake", /* loops = */ 1);
+ }
+ else {
+ dissolve ();
+ }
+}
+
+void UnstableTile::dissolve (void)
+{
+ if ((state != STATE_NORMAL) && (state != STATE_SHAKE))
+ return;
+
+ if (sprite->has_action ("dissolve")) {
+ state = STATE_DISSOLVE;
+ this->set_action ("dissolve", /* loops = */ 1);
+ }
+ else {
+ slow_fall ();
+ }
+}
+
+void UnstableTile::slow_fall (void)
+{
+ /* Only enter slow-fall if neither shake nor dissolve is available. */
+ if (state != STATE_NORMAL) {
+ this->fall_down ();
+ return;
+ }
+
+ if (sprite->has_action ("fall-down")) {
+ state = STATE_SLOWFALL;
+ this->set_action ("fall-down", /* loops = */ 1);
+ physic.set_gravity_modifier (.10);
+ physic.enable_gravity (true);
+ slowfall_timer = 0.5; /* Fall slowly for half a second. */
+ }
+ else {
+ remove_me ();
+ }
+}
+
+void UnstableTile::fall_down (void)
+{
+ if ((state != STATE_NORMAL)
+ && (state != STATE_SHAKE)
+ && (state != STATE_DISSOLVE)
+ && (state != STATE_SLOWFALL))
+ return;
+
+ if (sprite->has_action ("fall-down")) {
+ state = STATE_FALL;
+ this->set_action ("fall-down", /* loops = */ 1);
+ physic.set_gravity_modifier (.98);
+ physic.enable_gravity (true);
+ }
+ else {
+ remove_me ();
+ }