Subversion Repositories MK-Marlin

/**

 * Marlin 3D Printer Firmware

 * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]

 *

 * Based on Sprinter and grbl.

 * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program.  If not, see <http://www.gnu.org/licenses/>.

 *

 */

#include "MarlinConfig.h"

#if ENABLED(AUTO_BED_LEVELING_UBL)

  #include "Marlin.h"

  #include "ubl.h"

  #include "planner.h"

  #include "stepper.h"

  #include <avr/io.h>

  #include <math.h>

  #if AVR_AT90USB1286_FAMILY  // Teensyduino & Printrboard IDE extensions have compile errors without this

    inline void set_current_from_destination() { COPY(current_position, destination); }

  #else

    extern void set_current_from_destination();

  #endif

  #if !UBL_SEGMENTED

    void unified_bed_leveling::line_to_destination_cartesian(const float &feed_rate, const uint8_t extruder) {

      /**

       * Much of the nozzle movement will be within the same cell. So we will do as little computation

       * 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

       */

      #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_CART] },

              end[XYZE] = { destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_CART] };

        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_xi  = get_cell_index_x(end[X_AXIS]),

                cell_dest_yi  = get_cell_index_y(end[Y_AXIS]);

      if (g26_debug_flag) {

        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_CART]);

        SERIAL_CHAR(')');

        SERIAL_EOL();

        debug_current_and_destination(PSTR("Start of ubl.line_to_destination_cartesian()"));

      }

      // A move within the same cell needs no splitting

      if (cell_start_xi == cell_dest_xi && cell_start_yi == cell_dest_yi) {

        // For a move off the bed, use a constant Z raise

        if (!WITHIN(cell_dest_xi, 0, GRID_MAX_POINTS_X - 1) || !WITHIN(cell_dest_yi, 0, GRID_MAX_POINTS_Y - 1)) {

          // Note: There is no Z Correction in this case. We are off the grid and don't know what

          // a reasonable correction would be.  If the user has specified a UBL_Z_RAISE_WHEN_OFF_MESH

          // value, that will be used instead of a calculated (Bi-Linear interpolation) correction.

          const float z_raise = 0.0

            #ifdef UBL_Z_RAISE_WHEN_OFF_MESH

              + UBL_Z_RAISE_WHEN_OFF_MESH

            #endif

          ;

          planner.buffer_segment(end[X_AXIS], end[Y_AXIS], end[Z_AXIS] + z_raise, end[E_CART], feed_rate, extruder);

          set_current_from_destination();

          if (g26_debug_flag)

            debug_current_and_destination(PSTR("out of bounds in ubl.line_to_destination_cartesian()"));

          return;

        }

        FINAL_MOVE:

        // The distance is always MESH_X_DIST so multiply by the constant reciprocal.

        const float xratio = (end[X_AXIS] - mesh_index_to_xpos(cell_dest_xi)) * (1.0f / (MESH_X_DIST));

        float z1 = z_values[cell_dest_xi    ][cell_dest_yi    ] + xratio *

                  (z_values[cell_dest_xi + 1][cell_dest_yi    ] - z_values[cell_dest_xi][cell_dest_yi    ]),

              z2 = z_values[cell_dest_xi    ][cell_dest_yi + 1] + xratio *

                  (z_values[cell_dest_xi + 1][cell_dest_yi + 1] - z_values[cell_dest_xi][cell_dest_yi + 1]);

        if (cell_dest_xi >= GRID_MAX_POINTS_X - 1) z1 = z2 = 0.0;

        // X cell-fraction done. Interpolate the two Z offsets with the Y fraction for the final Z offset.

        const float yratio = (end[Y_AXIS] - mesh_index_to_ypos(cell_dest_yi)) * (1.0f / (MESH_Y_DIST)),

                    z0 = cell_dest_yi < GRID_MAX_POINTS_Y - 1 ? (z1 + (z2 - z1) * yratio) * planner.fade_scaling_factor_for_z(end[Z_AXIS]) : 0.0;

        // Undefined parts of the Mesh in z_values[][] are NAN.

        // Replace NAN corrections with 0.0 to prevent NAN propagation.

        planner.buffer_segment(end[X_AXIS], end[Y_AXIS], end[Z_AXIS] + (isnan(z0) ? 0.0 : z0), end[E_CART], feed_rate, extruder);

        if (g26_debug_flag)

          debug_current_and_destination(PSTR("FINAL_MOVE in ubl.line_to_destination_cartesian()"));

        set_current_from_destination();

        return;

      }

      /**

       * Past this point the move is known to cross one or more mesh lines. Check for the most common

       * case - crossing only one X or Y line - after details are worked out to reduce computation.

       */

      const float dx = end[X_AXIS] - start[X_AXIS],

                  dy = end[Y_AXIS] - start[Y_AXIS];

      const int left_flag = dx < 0.0 ? 1 : 0,

                down_flag = dy < 0.0 ? 1 : 0;

      const float adx = left_flag ? -dx : dx,

                  ady = down_flag ? -dy : dy;

      const int dxi = cell_start_xi == cell_dest_xi ? 0 : left_flag ? -1 : 1,

                dyi = cell_start_yi == cell_dest_yi ? 0 : down_flag ? -1 : 1;

      /**

       * Compute the extruder scaling factor for each partial move, checking for

       * zero-length moves that would result in an infinite scaling factor.

       * A float divide is required for this, but then it just multiplies.

       * Also select a scaling factor based on the larger of the X and Y

       * components. The larger of the two is used to preserve precision.

       */

      const bool use_x_dist = adx > ady;

      float on_axis_distance = use_x_dist ? dx : dy,

            e_position = end[E_CART] - start[E_CART],

            z_position = end[Z_AXIS] - start[Z_AXIS];

      const float e_normalized_dist = e_position / on_axis_distance,

                  z_normalized_dist = z_position / on_axis_distance;

      int current_xi = cell_start_xi,

          current_yi = cell_start_yi;

      const float m = dy / dx,

                  c = start[Y_AXIS] - m * start[X_AXIS];

      const bool inf_normalized_flag = (isinf(e_normalized_dist) != 0),

                 inf_m_flag = (isinf(m) != 0);

      /**

       * Handle vertical lines that stay within one column.

       * These need not be perfectly vertical.

       */

      if (dxi == 0) {             // Vertical line?

        current_yi += down_flag;  // Line going down? Just go to the bottom.

        while (current_yi != cell_dest_yi + down_flag) {

          current_yi += dyi;

          const float next_mesh_line_y = mesh_index_to_ypos(current_yi);

          /**

           * Skip the calculations for an infinite slope.

           * For others the next X is the same so this can continue.

           * Calculate X at the next Y mesh line.

           */

          const float rx = inf_m_flag ? start[X_AXIS] : (next_mesh_line_y - c) / m;

          float z0 = z_correction_for_x_on_horizontal_mesh_line(rx, current_xi, current_yi)

                     * planner.fade_scaling_factor_for_z(end[Z_AXIS]);

          // Undefined parts of the Mesh in z_values[][] are NAN.

          // Replace NAN corrections with 0.0 to prevent NAN propagation.

          if (isnan(z0)) z0 = 0.0;

          const float ry = mesh_index_to_ypos(current_yi);

          /**

           * Without this check, it's possible to generate a zero length move, as in the case where

           * the line is heading down, starting exactly on a mesh line boundary. Since this is rare

           * it might be fine to remove this check and let planner.buffer_segment() filter it out.

           */

          if (ry != start[Y_AXIS]) {

            if (!inf_normalized_flag) {

              on_axis_distance = use_x_dist ? rx - start[X_AXIS] : ry - start[Y_AXIS];

              e_position = start[E_CART] + on_axis_distance * e_normalized_dist;

              z_position = start[Z_AXIS] + on_axis_distance * z_normalized_dist;

            }

            else {

              e_position = end[E_CART];

              z_position = end[Z_AXIS];

            }

            planner.buffer_segment(rx, ry, z_position + z0, e_position, feed_rate, extruder);

          } //else printf("FIRST MOVE PRUNED  ");

        }

        if (g26_debug_flag)

          debug_current_and_destination(PSTR("vertical move done in ubl.line_to_destination_cartesian()"));

        // At the final destination? Usually not, but when on a Y Mesh Line it's completed.

        if (current_position[X_AXIS] != end[X_AXIS] || current_position[Y_AXIS] != end[Y_AXIS])

          goto FINAL_MOVE;

        set_current_from_destination();

        return;

      }

      /**

       * Handle horizontal lines that stay within one row.

       * These need not be perfectly horizontal.

       */

      if (dyi == 0) {             // Horizontal line?

        current_xi += left_flag;  // Heading left? Just go to the left edge of the cell for the first move.

        while (current_xi != cell_dest_xi + left_flag) {

          current_xi += dxi;

          const float next_mesh_line_x = mesh_index_to_xpos(current_xi),

                      ry = m * next_mesh_line_x + c;   // Calculate Y at the next X mesh line

          float z0 = z_correction_for_y_on_vertical_mesh_line(ry, current_xi, current_yi)

                     * planner.fade_scaling_factor_for_z(end[Z_AXIS]);

          // Undefined parts of the Mesh in z_values[][] are NAN.

          // Replace NAN corrections with 0.0 to prevent NAN propagation.

          if (isnan(z0)) z0 = 0.0;

          const float rx = mesh_index_to_xpos(current_xi);

          /**

           * Without this check, it's possible to generate a zero length move, as in the case where

           * the line is heading left, starting exactly on a mesh line boundary. Since this is rare

           * it might be fine to remove this check and let planner.buffer_segment() filter it out.

           */

          if (rx != start[X_AXIS]) {

            if (!inf_normalized_flag) {

              on_axis_distance = use_x_dist ? rx - start[X_AXIS] : ry - start[Y_AXIS];

              e_position = start[E_CART] + on_axis_distance * e_normalized_dist;  // is based on X or Y because this is a horizontal move

              z_position = start[Z_AXIS] + on_axis_distance * z_normalized_dist;

            }

            else {

              e_position = end[E_CART];

              z_position = end[Z_AXIS];

            }

            if (!planner.buffer_segment(rx, ry, z_position + z0, e_position, feed_rate, extruder))

              break;

          } //else printf("FIRST MOVE PRUNED  ");

        }

        if (g26_debug_flag)

          debug_current_and_destination(PSTR("horizontal move done in ubl.line_to_destination_cartesian()"));

        if (current_position[X_AXIS] != end[X_AXIS] || current_position[Y_AXIS] != end[Y_AXIS])

          goto FINAL_MOVE;

        set_current_from_destination();

        return;

      }

      /**

       *

       * Handle the generic case of a line crossing both X and Y Mesh lines.

       *

       */

      int xi_cnt = cell_start_xi - cell_dest_xi,

          yi_cnt = cell_start_yi - cell_dest_yi;

      if (xi_cnt < 0) xi_cnt = -xi_cnt;

      if (yi_cnt < 0) yi_cnt = -yi_cnt;

      current_xi += left_flag;

      current_yi += down_flag;

      while (xi_cnt || yi_cnt) {

        const float next_mesh_line_x = mesh_index_to_xpos(current_xi + dxi),

                    next_mesh_line_y = mesh_index_to_ypos(current_yi + dyi),

                    ry = m * next_mesh_line_x + c,   // Calculate Y at the next X mesh line

                    rx = (next_mesh_line_y - c) / m; // Calculate X at the next Y mesh line

                                                     // (No need to worry about m being zero.

                                                     //  If that was the case, it was already detected

                                                     //  as a vertical line move above.)

        if (left_flag == (rx > next_mesh_line_x)) { // Check if we hit the Y line first

          // Yes!  Crossing a Y Mesh Line next

          float z0 = z_correction_for_x_on_horizontal_mesh_line(rx, current_xi - left_flag, current_yi + dyi)

                     * planner.fade_scaling_factor_for_z(end[Z_AXIS]);

          // Undefined parts of the Mesh in z_values[][] are NAN.

          // Replace NAN corrections with 0.0 to prevent NAN propagation.

          if (isnan(z0)) z0 = 0.0;

          if (!inf_normalized_flag) {

            on_axis_distance = use_x_dist ? rx - start[X_AXIS] : next_mesh_line_y - start[Y_AXIS];

            e_position = start[E_CART] + on_axis_distance * e_normalized_dist;

            z_position = start[Z_AXIS] + on_axis_distance * z_normalized_dist;

          }

          else {

            e_position = end[E_CART];

            z_position = end[Z_AXIS];

          }

          if (!planner.buffer_segment(rx, next_mesh_line_y, z_position + z0, e_position, feed_rate, extruder))

            break;

          current_yi += dyi;

          yi_cnt--;

        }

        else {

          // Yes!  Crossing a X Mesh Line next

          float z0 = z_correction_for_y_on_vertical_mesh_line(ry, current_xi + dxi, current_yi - down_flag)

                     * planner.fade_scaling_factor_for_z(end[Z_AXIS]);

          // Undefined parts of the Mesh in z_values[][] are NAN.

          // Replace NAN corrections with 0.0 to prevent NAN propagation.

          if (isnan(z0)) z0 = 0.0;

          if (!inf_normalized_flag) {

            on_axis_distance = use_x_dist ? next_mesh_line_x - start[X_AXIS] : ry - start[Y_AXIS];

            e_position = start[E_CART] + on_axis_distance * e_normalized_dist;

            z_position = start[Z_AXIS] + on_axis_distance * z_normalized_dist;

          }

          else {

            e_position = end[E_CART];

            z_position = end[Z_AXIS];

          }

          if (!planner.buffer_segment(next_mesh_line_x, ry, z_position + z0, e_position, feed_rate, extruder))

            break;

          current_xi += dxi;

          xi_cnt--;

        }

        if (xi_cnt < 0 || yi_cnt < 0) break; // Too far! Exit the loop and go to FINAL_MOVE

      }

      if (g26_debug_flag)

        debug_current_and_destination(PSTR("generic move done in ubl.line_to_destination_cartesian()"));

      if (current_position[X_AXIS] != end[X_AXIS] || current_position[Y_AXIS] != end[Y_AXIS])

        goto FINAL_MOVE;

      set_current_from_destination();

    }

  #else // UBL_SEGMENTED

    #if IS_SCARA // scale the feed rate from mm/s to degrees/s

      static float scara_feed_factor, scara_oldA, scara_oldB;

    #endif

    // 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 (&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_IK(raw);

        planner.buffer_segment(delta[A_AXIS], delta[B_AXIS], delta[C_AXIS], in_raw[E_CART], fr, active_extruder);

      #elif ENABLED(HANGPRINTER)   // apply hangprinter inverse_kinematics

        HANGPRINTER_IK(raw);

        planner.buffer_segment(line_lengths[A_AXIS], line_lengths[B_AXIS], line_lengths[C_AXIS], line_lengths[D_AXIS], in_raw[E_CART], fr, active_extruder);

      #elif IS_SCARA  // apply scara inverse_kinematics (should be changed to save raw->logical->raw)

        inverse_kinematics(raw);  // this writes delta[ABC] from raw[XYZE]

                                  // should move the feedrate scaling to scara inverse_kinematics

        const float adiff = ABS(delta[A_AXIS] - scara_oldA),

                    bdiff = ABS(delta[B_AXIS] - scara_oldB);

        scara_oldA = delta[A_AXIS];

        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], in_raw[E_CART], s_feedrate, active_extruder);

      #else // CARTESIAN

        planner.buffer_segment(raw[X_AXIS], raw[Y_AXIS], raw[Z_AXIS], in_raw[E_CART], fr, active_extruder);

      #endif

    }

    #if IS_SCARA

      #define DELTA_SEGMENT_MIN_LENGTH 0.25 // SCARA minimum segment size is 0.25mm

    #elif ENABLED(DELTA)

      #define DELTA_SEGMENT_MIN_LENGTH 0.10 // mm (still subject to DELTA_SEGMENTS_PER_SECOND)

    #else // CARTESIAN

      #ifdef LEVELED_SEGMENT_LENGTH

        #define DELTA_SEGMENT_MIN_LENGTH LEVELED_SEGMENT_LENGTH

      #else

        #define DELTA_SEGMENT_MIN_LENGTH 1.00 // mm (similar to G2/G3 arc segmentation)

      #endif

    #endif

    /**

     * Prepare a segmented linear move for DELTA/SCARA/CARTESIAN with UBL and FADE semantics.

     * This calls planner.buffer_segment multiple times for small incremental moves.

     * 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) {

      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

      const float total[XYZE] = {

        rtarget[X_AXIS] - current_position[X_AXIS],

        rtarget[Y_AXIS] - current_position[Y_AXIS],

        rtarget[Z_AXIS] - current_position[Z_AXIS],

        rtarget[E_CART] - current_position[E_CART]

      };

      const float cartesian_xy_mm = HYPOT(total[X_AXIS], total[Y_AXIS]);  // total horizontal xy distance

      #if IS_KINEMATIC

        const float seconds = cartesian_xy_mm / feedrate;                                  // seconds to move xy distance at requested rate

        uint16_t segments = lroundf(delta_segments_per_second * seconds),                  // preferred number of segments for distance @ feedrate

                 seglimit = lroundf(cartesian_xy_mm * (1.0f / (DELTA_SEGMENT_MIN_LENGTH))); // number of segments at minimum segment length

        NOMORE(segments, seglimit);                                                        // limit to minimum segment length (fewer segments)

      #else

        uint16_t segments = lroundf(cartesian_xy_mm * (1.0f / (DELTA_SEGMENT_MIN_LENGTH))); // cartesian fixed segment length

      #endif

      NOLESS(segments, 1U);                        // must have at least one segment

      const float inv_segments = 1.0f / segments;  // divide once, multiply thereafter

      #if IS_SCARA // scale the feed rate from mm/s to degrees/s

        scara_feed_factor = cartesian_xy_mm * inv_segments * feedrate;

        scara_oldA = planner.get_axis_position_degrees(A_AXIS);

        scara_oldB = planner.get_axis_position_degrees(B_AXIS);

      #endif

      const float diff[XYZE] = {

        total[X_AXIS] * inv_segments,

        total[Y_AXIS] * inv_segments,

        total[Z_AXIS] * inv_segments,

        total[E_CART] * inv_segments

      };

      // Note that E segment distance could vary slightly as z mesh height

      // changes for each segment, but small enough to ignore.

      float raw[XYZE] = {

        current_position[X_AXIS],

        current_position[Y_AXIS],

        current_position[Z_AXIS],

        current_position[E_CART]

      };

      // Only compute leveling per segment if ubl active and target below z_fade_height.

      if (!planner.leveling_active || !planner.leveling_active_at_z(rtarget[Z_AXIS])) {   // no mesh leveling

        while (--segments) {

          LOOP_XYZE(i) raw[i] += diff[i];

          ubl_buffer_segment_raw(raw, feedrate);

        }

        ubl_buffer_segment_raw(rtarget, feedrate);

        return false; // moved but did not set_current_from_destination();

      }

      // Otherwise perform per-segment leveling

      #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)

        const float fade_scaling_factor = planner.fade_scaling_factor_for_z(rtarget[Z_AXIS]);

      #endif

      // increment to first segment destination

      LOOP_XYZE(i) raw[i] += diff[i];

      for (;;) {  // for each mesh cell encountered during the move

        // Compute mesh cell invariants that remain constant for all segments within cell.

        // Note for cell index, if point is outside the mesh grid (in MESH_INSET perimeter)

        // the bilinear interpolation from the adjacent cell within the mesh will still work.

        // Inner loop will exit each time (because out of cell bounds) but will come back

        // in top of loop and again re-find same adjacent cell and use it, just less efficient

        // for mesh inset area.

        int8_t cell_xi = (raw[X_AXIS] - (MESH_MIN_X)) * (1.0f / (MESH_X_DIST)),

               cell_yi = (raw[Y_AXIS] - (MESH_MIN_Y)) * (1.0f / (MESH_Y_DIST));

        cell_xi = constrain(cell_xi, 0, (GRID_MAX_POINTS_X) - 1);

        cell_yi = constrain(cell_yi, 0, (GRID_MAX_POINTS_Y) - 1);

        const float x0 = mesh_index_to_xpos(cell_xi),   // 64 byte table lookup avoids mul+add

                    y0 = mesh_index_to_ypos(cell_yi);

        float z_x0y0 = z_values[cell_xi  ][cell_yi  ],  // z at lower left corner

              z_x1y0 = z_values[cell_xi+1][cell_yi  ],  // z at upper left corner

              z_x0y1 = z_values[cell_xi  ][cell_yi+1],  // z at lower right corner

              z_x1y1 = z_values[cell_xi+1][cell_yi+1];  // z at upper right corner

        if (isnan(z_x0y0)) z_x0y0 = 0;              // ideally activating planner.leveling_active (G29 A)

        if (isnan(z_x1y0)) z_x1y0 = 0;              //   should refuse if any invalid mesh points

        if (isnan(z_x0y1)) z_x0y1 = 0;              //   in order to avoid isnan tests per cell,

        if (isnan(z_x1y1)) z_x1y1 = 0;              //   thus guessing zero for undefined points

        float cx = raw[X_AXIS] - x0,   // cell-relative x and y

              cy = raw[Y_AXIS] - y0;

        const float z_xmy0 = (z_x1y0 - z_x0y0) * (1.0f / (MESH_X_DIST)),   // z slope per x along y0 (lower left to lower right)

                    z_xmy1 = (z_x1y1 - z_x0y1) * (1.0f / (MESH_X_DIST));   // z slope per x along y1 (upper left to upper right)

              float z_cxy0 = z_x0y0 + z_xmy0 * cx;            // z height along y0 at cx (changes for each cx in cell)

        const float z_cxy1 = z_x0y1 + z_xmy1 * cx,            // z height along y1 at cx

                    z_cxyd = z_cxy1 - z_cxy0;                 // z height difference along cx from y0 to y1

              float z_cxym = z_cxyd * (1.0f / (MESH_Y_DIST));  // z slope per y along cx from y0 to y1 (changes for each cx in cell)

        //    float z_cxcy = z_cxy0 + z_cxym * cy;            // interpolated mesh z height along cx at cy (do inside the segment loop)

        // As subsequent segments step through this cell, the z_cxy0 intercept will change

        // and the z_cxym slope will change, both as a function of cx within the cell, and

        // each change by a constant for fixed segment lengths.

        const float z_sxy0 = z_xmy0 * diff[X_AXIS],                                     // per-segment adjustment to z_cxy0

                    z_sxym = (z_xmy1 - z_xmy0) * (1.0f / (MESH_Y_DIST)) * diff[X_AXIS];  // per-segment adjustment to z_cxym

        for (;;) {  // for all segments within this mesh cell

          if (--segments == 0)                      // if this is last segment, use rtarget for exact

            COPY(raw, rtarget);

          const float z_cxcy = (z_cxy0 + z_cxym * cy) // interpolated mesh z height along cx at cy

            #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)

              * fade_scaling_factor                   // apply fade factor to interpolated mesh height

            #endif

          ;

          const float z = raw[Z_AXIS];

          raw[Z_AXIS] += z_cxcy;

          ubl_buffer_segment_raw(raw, feedrate);

          raw[Z_AXIS] = z;

          if (segments == 0)                        // done with last segment

            return false;                           // did not set_current_from_destination()

          LOOP_XYZE(i) raw[i] += diff[i];

          cx += diff[X_AXIS];

          cy += diff[Y_AXIS];

          if (!WITHIN(cx, 0, MESH_X_DIST) || !WITHIN(cy, 0, MESH_Y_DIST))    // done within this cell, break to next

            break;

          // Next segment still within same mesh cell, adjust the per-segment

          // slope and intercept to compute next z height.

          z_cxy0 += z_sxy0;   // adjust z_cxy0 by per-segment z_sxy0

          z_cxym += z_sxym;   // adjust z_cxym by per-segment z_sxym

        } // segment loop

      } // cell loop

      return false; // caller will update current_position

    }

  #endif // UBL_SEGMENTED

#endif // AUTO_BED_LEVELING_UBL