UBL_DELTA post merge cleanup (#6705)

* UBL_DELTA post merge cleanup:
   fix fade_height, lost during some previous merge
   fix float cx,cy which are not const
   move repeated z_cxcy calc line inside loop
   style fixes and comment fixes/alignment

* Update ubl_motion.cpp

remove unnecessary parentheses

* Update Conditionals_post.h

Change name of define to more accurate meaning:
UBL_GRANULAR_SEGMENTATION_FOR_CARTESIAN
which is not and should not be the default for cartesians with UBL.

Marlin/Conditionals_post.h

@@ -731,7 +731,7 @@
    * Set granular options based on the specific type of leveling
    */
 
-  #define UBL_DELTA  (ENABLED(AUTO_BED_LEVELING_UBL) && ENABLED(DELTA))
+  #define UBL_DELTA  (ENABLED(AUTO_BED_LEVELING_UBL) && (ENABLED(DELTA) || ENABLED(UBL_GRANULAR_SEGMENTATION_FOR_CARTESIAN)))
   #define ABL_PLANAR (ENABLED(AUTO_BED_LEVELING_LINEAR) || ENABLED(AUTO_BED_LEVELING_3POINT))
   #define ABL_GRID   (ENABLED(AUTO_BED_LEVELING_LINEAR) || ENABLED(AUTO_BED_LEVELING_BILINEAR))
   #define HAS_ABL    (ABL_PLANAR || ABL_GRID || ENABLED(AUTO_BED_LEVELING_UBL))

Marlin/ubl_motion.cpp

@@ -570,6 +570,10 @@
 
       // Otherwise perform per-segment leveling
 
+      #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)
+        const float fade_scaling_factor = ubl.fade_scaling_factor_for_z(ltarget[Z_AXIS]);
+      #endif
+
       float seg_dest[XYZE];  // per-segment destination, initialize to first segment
       LOOP_XYZE(i) seg_dest[i] = current_position[i] + segment_distance[i];
 
@@ -619,8 +623,9 @@
         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 * (1.0 / (MESH_Y_DIST)),  // z slope per y along cx from y0 to y1
+              float z_cxym = z_cxyd * (1.0 / (MESH_Y_DIST));  // z slope per y along cx from y0 to y1
-                    z_cxcy = z_cxy0 + z_cxym * cy;          // z height along cx at cy
+        
+        //    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
@@ -631,9 +636,15 @@
 
         do {  // for all segments within this mesh cell
 
-          z_cxcy += ubl.state.z_offset;
+          float z_cxcy = z_cxy0 + z_cxym * cy;      // interpolated mesh z height along cx at cy
 
-          if (--segments == 0) {          // this is last segment, use ltarget for exact
+          #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)
+            z_cxcy *= fade_scaling_factor;          // apply fade factor to interpolated mesh height
+          #endif
+        
+          z_cxcy += ubl.state.z_offset;             // add fixed mesh offset from G29 Z
+
+          if (--segments == 0) {                    // if this is last segment, use ltarget for exact
             COPY(seg_dest, ltarget);
             seg_dest[Z_AXIS] += z_cxcy;
             ubl_buffer_line_segment(seg_dest, feedrate, active_extruder);
@@ -657,11 +668,10 @@
           }
 
           // Next segment still within same mesh cell, adjust the per-segment
-          // slope and intercept and compute next z height.
+          // 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
-          z_cxcy  = z_cxy0 + z_cxym * cy;   // recompute z_cxcy from adjusted slope and intercept
 
         } while (true);   // per-segment loop exits by break after last segment within cell, or by return on final segment
       } while (true);   // per-cell loop