Skew Correction for UBL

Also remove unused grid slicing function when using UBL segmented.

Marlin/src/feature/bedlevel/ubl/ubl.h

       return i < GRID_MAX_POINTS_Y ? pgm_read_float(&_mesh_index_to_ypos[i]) : MESH_MIN_Y + i * (MESH_Y_DIST);
     }
 
-    static bool prepare_segmented_line_to(const float rtarget[XYZE], const float &feedrate);
     static void line_to_destination_cartesian(const float &fr, const uint8_t e);
+    static bool prepare_segmented_line_to(const float (&rtarget)[XYZE], const float &feedrate);
 
     #define _CMPZ(a,b) (z_values[a][b] == z_values[a][b+1])
     #define CMPZ(a) (_CMPZ(a, 0) && _CMPZ(a, 1))

Marlin/src/feature/bedlevel/ubl/ubl_motion.cpp

      * as possible to determine if this is the case. If this move is within the same cell, we will
      * just do the required Z-Height correction, call the Planner's buffer_line() routine, and leave
      */
-    const float start[XYZE] = {
-                  current_position[X_AXIS],
-                  current_position[Y_AXIS],
-                  current_position[Z_AXIS],
-                  current_position[E_AXIS]
-                },
-                end[XYZE] = {
-                  destination[X_AXIS],
-                  destination[Y_AXIS],
-                  destination[Z_AXIS],
-                  destination[E_AXIS]
-                };
+    #if ENABLED(SKEW_CORRECTION)
+      // For skew correction just adjust the destination point and we're done
+      float start[XYZE] = { current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS] },
+            end[XYZE] = { destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS] };
+      planner.skew(start[X_AXIS], start[Y_AXIS], start[Z_AXIS]);
+      planner.skew(end[X_AXIS], end[Y_AXIS], end[Z_AXIS]);
+    #else
+      const float (&start)[XYZE] = current_position,
+                    (&end)[XYZE] = destination;
+    #endif
 
     const int cell_start_xi = get_cell_index_x(start[X_AXIS]),
               cell_start_yi = get_cell_index_y(start[Y_AXIS]),
               cell_dest_yi  = get_cell_index_y(end[Y_AXIS]);
 
     if (g26_debug_flag) {
-      SERIAL_ECHOPAIR(" ubl.line_to_destination(xe=", end[X_AXIS]);
-      SERIAL_ECHOPAIR(", ye=", end[Y_AXIS]);
-      SERIAL_ECHOPAIR(", ze=", end[Z_AXIS]);
-      SERIAL_ECHOPAIR(", ee=", end[E_AXIS]);
+      SERIAL_ECHOPAIR(" ubl.line_to_destination_cartesian(xe=", destination[X_AXIS]);
+      SERIAL_ECHOPAIR(", ye=", destination[Y_AXIS]);
+      SERIAL_ECHOPAIR(", ze=", destination[Z_AXIS]);
+      SERIAL_ECHOPAIR(", ee=", destination[E_AXIS]);
       SERIAL_CHAR(')');
       SERIAL_EOL();
       debug_current_and_destination(PSTR("Start of ubl.line_to_destination_cartesian()"));
     // We don't want additional apply_leveling() performed by regular buffer_line or buffer_line_kinematic,
     // so we call buffer_segment directly here.  Per-segmented leveling and kinematics performed first.
 
-    inline void _O2 ubl_buffer_segment_raw(const float (&raw)[XYZE], const float &fr) {
+    inline void _O2 ubl_buffer_segment_raw(const float (&in_raw)[XYZE], const float &fr) {
+
+      #if ENABLED(SKEW_CORRECTION)
+        float raw[XYZE] = { in_raw[X_AXIS], in_raw[Y_AXIS], in_raw[Z_AXIS] };
+        planner.skew(raw[X_AXIS], raw[Y_AXIS], raw[Z_AXIS]);
+      #else
+        const float (&raw)[XYZE] = in_raw;
+      #endif
 
       #if ENABLED(DELTA)  // apply delta inverse_kinematics
 
         DELTA_RAW_IK();
-        planner.buffer_segment(delta[A_AXIS], delta[B_AXIS], delta[C_AXIS], raw[E_AXIS], fr, active_extruder);
+        planner.buffer_segment(delta[A_AXIS], delta[B_AXIS], delta[C_AXIS], in_raw[E_AXIS], fr, active_extruder);
 
       #elif IS_SCARA  // apply scara inverse_kinematics (should be changed to save raw->logical->raw)
 
         scara_oldB = delta[B_AXIS];
         float s_feedrate = max(adiff, bdiff) * scara_feed_factor;
 
-        planner.buffer_segment(delta[A_AXIS], delta[B_AXIS], delta[C_AXIS], raw[E_AXIS], s_feedrate, active_extruder);
+        planner.buffer_segment(delta[A_AXIS], delta[B_AXIS], delta[C_AXIS], in_raw[E_AXIS], s_feedrate, active_extruder);
 
       #else // CARTESIAN
 
-        planner.buffer_segment(raw[X_AXIS], raw[Y_AXIS], raw[Z_AXIS], raw[E_AXIS], fr, active_extruder);
+        planner.buffer_segment(raw[X_AXIS], raw[Y_AXIS], raw[Z_AXIS], in_raw[E_AXIS], fr, active_extruder);
 
       #endif
     }
      * Returns true if did NOT move, false if moved (requires current_position update).
      */
 
-    bool _O2 unified_bed_leveling::prepare_segmented_line_to(const float rtarget[XYZE], const float &feedrate) {
+    bool _O2 unified_bed_leveling::prepare_segmented_line_to(const float (&rtarget)[XYZE], const float &feedrate) {
 
       if (!position_is_reachable(rtarget[X_AXIS], rtarget[Y_AXIS]))  // fail if moving outside reachable boundary
         return true; // did not move, so current_position still accurate

Marlin/src/module/planner.cpp

   void Planner::apply_leveling(float &rx, float &ry, float &rz) {
 
     #if ENABLED(SKEW_CORRECTION)
-      if (WITHIN(rx, X_MIN_POS + 1, X_MAX_POS) && WITHIN(ry, Y_MIN_POS + 1, Y_MAX_POS)) {
-        const float tempry = ry - (rz * planner.yz_skew_factor),
-                    temprx = rx - (ry * planner.xy_skew_factor) - (rz * (planner.xz_skew_factor - (planner.xy_skew_factor * planner.yz_skew_factor)));
-        if (WITHIN(temprx, X_MIN_POS, X_MAX_POS) && WITHIN(tempry, Y_MIN_POS, Y_MAX_POS)) {
-          rx = temprx;
-          ry = tempry;
-        }
-      }
+      skew(rx, ry, rz);
     #endif
 
     if (!leveling_active) return;
     }
 
     #if ENABLED(SKEW_CORRECTION)
-      if (WITHIN(raw[X_AXIS], X_MIN_POS, X_MAX_POS) && WITHIN(raw[Y_AXIS], Y_MIN_POS, Y_MAX_POS)) {
-        const float temprx = raw[X_AXIS] + raw[Y_AXIS] * planner.xy_skew_factor + raw[Z_AXIS] * planner.xz_skew_factor,
-                    tempry = raw[Y_AXIS] + raw[Z_AXIS] * planner.yz_skew_factor;
-        if (WITHIN(temprx, X_MIN_POS, X_MAX_POS) && WITHIN(tempry, Y_MIN_POS, Y_MAX_POS)) {
-          raw[X_AXIS] = temprx;
-          raw[Y_AXIS] = tempry;
-        }
-      }
+      unskew(raw[X_AXIS], raw[Y_AXIS], raw[Z_AXIS]);
     #endif
   }
 

Marlin/src/module/planner.h

 
     #endif
 
+    #if ENABLED(SKEW_CORRECTION)
+
+      FORCE_INLINE static void skew(float &cx, float &cy, const float &cz) {
+        if (WITHIN(cx, X_MIN_POS + 1, X_MAX_POS) && WITHIN(cy, Y_MIN_POS + 1, Y_MAX_POS)) {
+          const float sx = cx - (cy * xy_skew_factor) - (cz * (xz_skew_factor - (xy_skew_factor * yz_skew_factor))),
+                      sy = cy - (cz * yz_skew_factor);
+          if (WITHIN(sx, X_MIN_POS, X_MAX_POS) && WITHIN(sy, Y_MIN_POS, Y_MAX_POS)) {
+            cx = sx; cy = sy;
+          }
+        }
+      }
+
+      FORCE_INLINE static void unskew(float &cx, float &cy, const float &cz) {
+        if (WITHIN(cx, X_MIN_POS, X_MAX_POS) && WITHIN(cy, Y_MIN_POS, Y_MAX_POS)) {
+          const float sx = cx + cy * xy_skew_factor + cz * xz_skew_factor,
+                      sy = cy + cz * yz_skew_factor;
+          if (WITHIN(sx, X_MIN_POS, X_MAX_POS) && WITHIN(sy, Y_MIN_POS, Y_MAX_POS)) {
+            cx = sx; cy = sy;
+          }
+        }
+      }
+
+    #endif // SKEW_CORRECTION
+
     #if PLANNER_LEVELING
 
       #define ARG_X float rx