Add pre-calculated planner.e_factor

Marlin/src/feature/fwretract.cpp

   set_destination_from_current();
   stepper.synchronize();  // Wait for buffered moves to complete
 
-  const float renormalize = 100.0 / planner.flow_percentage[active_extruder] / planner.volumetric_multiplier[active_extruder];
+  const float renormalize = 1.0 / planner.e_factor[active_extruder];
 
   if (retracting) {
     // Retract by moving from a faux E position back to the current E position

Marlin/src/feature/pause.cpp

 }
 
 void do_pause_e_move(const float &length, const float fr) {
-  current_position[E_AXIS] += length * 100.0 / planner.flow_percentage[active_extruder] / planner.volumetric_multiplier[active_extruder];
+  current_position[E_AXIS] += length / planner.e_factor[active_extruder];
   set_destination_from_current();
   #if IS_KINEMATIC
     planner.buffer_line_kinematic(destination, fr, active_extruder);

Marlin/src/gcode/config/M221.cpp

  */
 void GcodeSuite::M221() {
   if (get_target_extruder_from_command()) return;
-  if (parser.seenval('S'))
+  if (parser.seenval('S')) {
     planner.flow_percentage[target_extruder] = parser.value_int();
+    planner.refresh_e_factor(target_extruder);
+  }
 }

Marlin/src/lcd/ultralcd.cpp

     #endif
   #endif
 
+  // Refresh the E factor after changing flow
+  inline void _lcd_refresh_e_factor_0() { planner.refresh_e_factor(0); }
+  #if EXTRUDERS > 1
+    inline void _lcd_refresh_e_factor() { planner.refresh_e_factor(active_extruder); }
+    inline void _lcd_refresh_e_factor_1() { planner.refresh_e_factor(1); }
+    #if EXTRUDERS > 2
+      inline void _lcd_refresh_e_factor_2() { planner.refresh_e_factor(2); }
+      #if EXTRUDERS > 3
+        inline void _lcd_refresh_e_factor_3() { planner.refresh_e_factor(3); }
+        #if EXTRUDERS > 4
+          inline void _lcd_refresh_e_factor_4() { planner.refresh_e_factor(4); }
+        #endif // EXTRUDERS > 4
+      #endif // EXTRUDERS > 3
+    #endif // EXTRUDERS > 2
+  #endif // EXTRUDERS > 1
+
   /**
    *
    * "Tune" submenu
     // Flow [1-5]:
     //
     #if EXTRUDERS == 1
-      MENU_ITEM_EDIT(int3, MSG_FLOW, &planner.flow_percentage[0], 10, 999);
+      MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW, &planner.flow_percentage[0], 10, 999, _lcd_refresh_e_factor_0);
     #else // EXTRUDERS > 1
-      MENU_ITEM_EDIT(int3, MSG_FLOW, &planner.flow_percentage[active_extruder], 10, 999);
-      MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N1, &planner.flow_percentage[0], 10, 999);
-      MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N2, &planner.flow_percentage[1], 10, 999);
+      MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW, &planner.flow_percentage[active_extruder], 10, 999, _lcd_refresh_e_factor);
+      MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW MSG_N1, &planner.flow_percentage[0], 10, 999, _lcd_refresh_e_factor_0);
+      MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW MSG_N2, &planner.flow_percentage[1], 10, 999, _lcd_refresh_e_factor_1);
       #if EXTRUDERS > 2
-        MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N3, &planner.flow_percentage[2], 10, 999);
+        MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW MSG_N3, &planner.flow_percentage[2], 10, 999, _lcd_refresh_e_factor_2);
         #if EXTRUDERS > 3
-          MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N4, &planner.flow_percentage[3], 10, 999);
+          MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW MSG_N4, &planner.flow_percentage[3], 10, 999, _lcd_refresh_e_factor_3);
           #if EXTRUDERS > 4
-            MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N5, &planner.flow_percentage[4], 10, 999);
+            MENU_ITEM_EDIT_CALLBACK(int3, MSG_FLOW MSG_N5, &planner.flow_percentage[4], 10, 999, _lcd_refresh_e_factor_4);
           #endif // EXTRUDERS > 4
         #endif // EXTRUDERS > 3
       #endif // EXTRUDERS > 2

Marlin/src/module/configuration_store.cpp

  *  533  M208 R    swap_retract_recover_feedrate_mm_s (float)
  *
  * Volumetric Extrusion:                            21 bytes
- *  537  M200 D    volumetric_enabled               (bool)
- *  538  M200 T D  filament_size                    (float x5) (T0..3)
+ *  537  M200 D    parser.volumetric_enabled        (bool)
+ *  538  M200 T D  planner.filament_size            (float x5) (T0..3)
  *
  * HAVE_TMC2130:                                    22 bytes
  *  558  M906 X    Stepper X current                (uint16_t)

Marlin/src/module/motion.cpp

           }
         #endif // PREVENT_COLD_EXTRUSION
         #if ENABLED(PREVENT_LENGTHY_EXTRUDE)
-          if (FABS(destination[E_AXIS] - current_position[E_AXIS]) > (EXTRUDE_MAXLENGTH) / planner.volumetric_multiplier[active_extruder]) {
+          if (FABS(destination[E_AXIS] - current_position[E_AXIS]) * planner.e_factor[active_extruder] > (EXTRUDE_MAXLENGTH)) {
             current_position[E_AXIS] = destination[E_AXIS]; // Behave as if the move really took place, but ignore E part
             SERIAL_ECHO_START();
             SERIAL_ECHOLNPGM(MSG_ERR_LONG_EXTRUDE_STOP);

Marlin/src/module/planner.cpp

 int16_t Planner::flow_percentage[EXTRUDERS] = ARRAY_BY_EXTRUDERS1(100); // Extrusion factor for each extruder
 
 // Initialized by settings.load()
-float Planner::filament_size[EXTRUDERS],         // As a baseline for the multiplier, filament diameter
+float Planner::e_factor[EXTRUDERS],              // The flow percentage and volumetric multiplier combine to scale E movement
+      Planner::filament_size[EXTRUDERS],         // As a baseline for the multiplier, filament diameter
       Planner::volumetric_multiplier[EXTRUDERS]; // May be auto-adjusted by a filament width sensor
 
 uint32_t Planner::max_acceleration_steps_per_s2[XYZE_N],
 }
 
 void Planner::calculate_volumetric_multipliers() {
-  for (uint8_t i = 0; i < COUNT(filament_size); i++)
+  for (uint8_t i = 0; i < COUNT(filament_size); i++) {
     volumetric_multiplier[i] = calculate_volumetric_multiplier(filament_size[i]);
+    refresh_e_factor(i);
+  }
 }
 
 #if PLANNER_LEVELING
 
   long de = target[E_AXIS] - position[E_AXIS];
 
-  const float e_factor = volumetric_multiplier[extruder] * flow_percentage[extruder] * 0.01;
-
   #if ENABLED(LIN_ADVANCE)
     float de_float = e - position_float[E_AXIS]; // Should this include e_factor?
   #endif
         }
       #endif // PREVENT_COLD_EXTRUSION
       #if ENABLED(PREVENT_LENGTHY_EXTRUDE)
-        const int32_t de_mm = labs(de * e_factor);
-        if (de_mm > (int32_t)axis_steps_per_mm[E_AXIS_N] * (EXTRUDE_MAXLENGTH)) { // It's not important to get max. extrusion length in a precision < 1mm, so save some cycles and cast to int
+        if (labs(de * e_factor[extruder]) > (int32_t)axis_steps_per_mm[E_AXIS_N] * (EXTRUDE_MAXLENGTH)) { // It's not important to get max. extrusion length in a precision < 1mm, so save some cycles and cast to int
           position[E_AXIS] = target[E_AXIS]; // Behave as if the move really took place, but ignore E part
           de = 0; // no difference
           #if ENABLED(LIN_ADVANCE)
   #endif
   if (de < 0) SBI(dm, E_AXIS);
 
-  const float esteps_float = de * e_factor;
+  const float esteps_float = de * e_factor[extruder];
   const int32_t esteps = abs(esteps_float) + 0.5;
 
   // Calculate the buffer head after we push this byte

Marlin/src/module/planner.h

 
     static int16_t flow_percentage[EXTRUDERS];  // Extrusion factor for each extruder
 
-    static float filament_size[EXTRUDERS],          // diameter of filament (in millimeters), typically around 1.75 or 2.85, 0 disables the volumetric calculations for the extruder
+    static float e_factor[EXTRUDERS],               // The flow percentage and volumetric multiplier combine to scale E movement
+                 filament_size[EXTRUDERS],          // diameter of filament (in millimeters), typically around 1.75 or 2.85, 0 disables the volumetric calculations for the extruder
                  volumetric_multiplier[EXTRUDERS];  // Reciprocal of cross-sectional area of filament (in mm^2). Pre-calculated to reduce computation in the planner
                                                     // May be auto-adjusted by a filament width sensor
 
     static void reset_acceleration_rates();
     static void refresh_positioning();
 
+    FORCE_INLINE static void refresh_e_factor(const uint8_t e) {
+      e_factor[e] = volumetric_multiplier[e] * flow_percentage[e] * 0.01;
+    }
+
     // Manage fans, paste pressure, etc.
     static void check_axes_activity();
 

Marlin/src/module/temperature.cpp

       // the nominal filament diameter then square it to get an area
       const float vmroot = measurement_delay[meas_shift_index] * 0.01 + 1.0;
       planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM] = vmroot <= 0.1 ? 0.01 : sq(vmroot);
+      planner.refresh_e_factor(FILAMENT_SENSOR_EXTRUDER_NUM);
     }
   #endif // FILAMENT_WIDTH_SENSOR