Merge pull request #5493 from thinkyhead/rc_fix_recover_unhop

Prevent retract un-hop at wrong height

Marlin/Marlin_main.cpp

 
   void retract(bool retracting, bool swapping = false) {
 
+    static float hop_height;
+
     if (retracting == retracted[active_extruder]) return;
 
     float old_feedrate_mm_s = feedrate_mm_s;
       prepare_move_to_destination();
 
       if (retract_zlift > 0.01) {
+        hop_height = current_position[Z_AXIS];
+        // Pretend current position is lower
         current_position[Z_AXIS] -= retract_zlift;
         SYNC_PLAN_POSITION_KINEMATIC();
+        // Raise up to the old current_position
         prepare_move_to_destination();
       }
     }
     else {
 
-      if (retract_zlift > 0.01) {
+      // If the height hasn't been altered, undo the Z hop
+      if (retract_zlift > 0.01 && hop_height == current_position[Z_AXIS]) {
+        // Pretend current position is higher. Z will lower on the next move
         current_position[Z_AXIS] += retract_zlift;
         SYNC_PLAN_POSITION_KINEMATIC();
       }
       float move_e = swapping ? retract_length_swap + retract_recover_length_swap : retract_length + retract_recover_length;
       current_position[E_AXIS] -= move_e / volumetric_multiplier[active_extruder];
       sync_plan_position_e();
+
+      // Lower Z and recover E
       prepare_move_to_destination();
     }