Change G26 circle angles

To prevent the nozzle from colliding with the printed pattern.

Marlin/src/gcode/bedlevel/G26.cpp

 #define PRIME_LENGTH 10.0
 #define OOZE_AMOUNT 0.3
 
-#define SIZE_OF_INTERSECTION_CIRCLES 5
-#define SIZE_OF_CROSSHAIRS 3
+#define INTERSECTION_CIRCLE_RADIUS 5
+#define CROSSHAIRS_SIZE 3
 
-#if SIZE_OF_CROSSHAIRS >= SIZE_OF_INTERSECTION_CIRCLES
-  #error "SIZE_OF_CROSSHAIRS must be less than SIZE_OF_INTERSECTION_CIRCLES."
+#if CROSSHAIRS_SIZE >= INTERSECTION_CIRCLE_RADIUS
+  #error "CROSSHAIRS_SIZE must be less than INTERSECTION_CIRCLE_RADIUS."
 #endif
 
 #define G26_OK false
 
   // If the end point of the line is closer to the nozzle, flip the direction,
   // moving from the end to the start. On very small lines the optimization isn't worth it.
-  if (dist_end < dist_start && (SIZE_OF_INTERSECTION_CIRCLES) < FABS(line_length))
+  if (dist_end < dist_start && (INTERSECTION_CIRCLE_RADIUS) < FABS(line_length))
     return print_line_from_here_to_there(ex, ey, ez, sx, sy, sz);
 
   // Decide whether to retract & bump
             // We found two circles that need a horizontal line to connect them
             // Print it!
             //
-            sx = _GET_MESH_X(  i  ) + (SIZE_OF_INTERSECTION_CIRCLES - (SIZE_OF_CROSSHAIRS)); // right edge
-            ex = _GET_MESH_X(i + 1) - (SIZE_OF_INTERSECTION_CIRCLES - (SIZE_OF_CROSSHAIRS)); // left edge
+            sx = _GET_MESH_X(  i  ) + (INTERSECTION_CIRCLE_RADIUS - (CROSSHAIRS_SIZE)); // right edge
+            ex = _GET_MESH_X(i + 1) - (INTERSECTION_CIRCLE_RADIUS - (CROSSHAIRS_SIZE)); // left edge
 
             sx = constrain(sx, X_MIN_POS + 1, X_MAX_POS - 1);
             sy = ey = constrain(_GET_MESH_Y(j), Y_MIN_POS + 1, Y_MAX_POS - 1);
               // We found two circles that need a vertical line to connect them
               // Print it!
               //
-              sy = _GET_MESH_Y(  j  ) + (SIZE_OF_INTERSECTION_CIRCLES - (SIZE_OF_CROSSHAIRS)); // top edge
-              ey = _GET_MESH_Y(j + 1) - (SIZE_OF_INTERSECTION_CIRCLES - (SIZE_OF_CROSSHAIRS)); // bottom edge
+              sy = _GET_MESH_Y(  j  ) + (INTERSECTION_CIRCLE_RADIUS - (CROSSHAIRS_SIZE)); // top edge
+              ey = _GET_MESH_Y(j + 1) - (INTERSECTION_CIRCLE_RADIUS - (CROSSHAIRS_SIZE)); // bottom edge
 
               sx = ex = constrain(_GET_MESH_X(i), X_MIN_POS + 1, X_MAX_POS - 1);
               sy = constrain(sy, Y_MIN_POS + 1, Y_MAX_POS - 1);
  */
 void GcodeSuite::G26() {
   SERIAL_ECHOLNPGM("G26 command started. Waiting for heater(s).");
-  float tmp, start_angle, end_angle;
-  int   i, xi, yi;
-  mesh_index_pair location;
 
   // Don't allow Mesh Validation without homing first,
   // or if the parameter parsing did not go OK, abort
   //debug_current_and_destination(PSTR("Starting G26 Mesh Validation Pattern."));
 
   /**
-   * Declare and generate a sin() & cos() table to be used during the circle drawing. This will lighten
-   * the CPU load and make the arc drawing faster and more smooth
+   * Pre-generate radius offset values at 30 degree intervals to reduce CPU load.
+   * All angles are offset by 15 degrees to allow for a smaller table.
    */
-  float sin_table[360 / 30 + 1], cos_table[360 / 30 + 1];
-  for (i = 0; i <= 360 / 30; i++) {
-    cos_table[i] = SIZE_OF_INTERSECTION_CIRCLES * cos(RADIANS(valid_trig_angle(i * 30.0)));
-    sin_table[i] = SIZE_OF_INTERSECTION_CIRCLES * sin(RADIANS(valid_trig_angle(i * 30.0)));
-  }
+  #define A_CNT ((360 / 30) / 2)
+  #define _COS(A) (trig_table[((N + A_CNT * 8) % A_CNT)] * (A >= A_CNT ? -1 : 1))
+  #define _SIN(A) (-_COS((A + A_CNT / 2) % (A_CNT * 2)))
+  float trig_table[A_CNT];
+  for (uint8_t i = 0; i < A_CNT; i++)
+    trig_table[i] = INTERSECTION_CIRCLE_RADIUS * cos(RADIANS(i * 30 + 15));
 
   do {
-    location = g26_continue_with_closest
+    const mesh_index_pair location = g26_continue_with_closest
       ? find_closest_circle_to_print(current_position[X_AXIS], current_position[Y_AXIS])
       : find_closest_circle_to_print(g26_x_pos, g26_y_pos); // Find the closest Mesh Intersection to where we are now.
 
                   circle_y = _GET_MESH_Y(location.y_index);
 
       // If this mesh location is outside the printable_radius, skip it.
-
       if (!position_is_reachable(circle_x, circle_y)) continue;
 
-      xi = location.x_index;  // Just to shrink the next few lines and make them easier to understand
-      yi = location.y_index;
-
+      // Determine where to start and end the circle,
+      // which is always drawn counter-clockwise.
+      const uint8_t xi = location.x_index, yi = location.y_index;
+      const bool f = yi == 0, r = xi == GRID_MAX_POINTS_X - 1, b = yi == GRID_MAX_POINTS_Y - 1;
+      int8_t start_ind = -2, end_ind = 10;  // Assume a full circle (from 4:30 to 4:30)
+      if (xi == 0) {                        // Left edge? Just right half.
+        start_ind = f ?  0 : -3;            // 05:30 (02:30 for front-left)
+        end_ind   = b ? -1 :  2;            // 12:30 (03:30 for back-left)
+      }
+      else if (r) {                         // Right edge? Just left half.
+        start_ind = f ? 5 : 3;              // 11:30 (09:30 for front-right)
+        end_ind   = b ? 6 : 8;              // 06:30 (08:30 for back-right)
+      }
+      else if (f) {                         // Front edge? Just back half.
+        start_ind = 0;                      // 02:30
+        end_ind   = 5;                      // 09:30
+      }
+      else if (b) {                         // Back edge? Just front half.
+        start_ind =  6;                     // 08:30
+        end_ind   = 11;                     // 03:30
+      }
       if (g26_debug_flag) {
         SERIAL_ECHOPAIR("   Doing circle at: (xi=", xi);
         SERIAL_ECHOPAIR(", yi=", yi);
         SERIAL_EOL();
       }
 
-      start_angle = 0.0;    // assume it is going to be a full circle
-      end_angle   = 360.0;
-      if (xi == 0) {       // Check for bottom edge
-        start_angle = -90.0;
-        end_angle   =  90.0;
-        if (yi == 0)        // it is an edge, check for the two left corners
-          start_angle = 0.0;
-        else if (yi == GRID_MAX_POINTS_Y - 1)
-          end_angle = 0.0;
-      }
-      else if (xi == GRID_MAX_POINTS_X - 1) { // Check for top edge
-        start_angle =  90.0;
-        end_angle   = 270.0;
-        if (yi == 0)                  // it is an edge, check for the two right corners
-          end_angle = 180.0;
-        else if (yi == GRID_MAX_POINTS_Y - 1)
-          start_angle = 180.0;
-      }
-      else if (yi == 0) {
-        start_angle =   0.0;         // only do the top   side of the cirlce
-        end_angle   = 180.0;
-      }
-      else if (yi == GRID_MAX_POINTS_Y - 1) {
-        start_angle = 180.0;         // only do the bottom side of the cirlce
-        end_angle   = 360.0;
-      }
-
-      for (tmp = start_angle; tmp < end_angle - 0.1; tmp += 30.0) {
+      for (int8_t ind = start_ind; ind < end_ind; ind++) {
 
         #if ENABLED(NEWPANEL)
-          if (user_canceled()) goto LEAVE;              // Check if the user wants to stop the Mesh Validation
+          if (user_canceled()) goto LEAVE;          // Check if the user wants to stop the Mesh Validation
         #endif
 
-        int tmp_div_30 = tmp / 30.0;
-        if (tmp_div_30 < 0) tmp_div_30 += 360 / 30;
-        if (tmp_div_30 > 11) tmp_div_30 -= 360 / 30;
+        float rx = circle_x + _COS(ind),            // For speed, these are now a lookup table entry
+              ry = circle_y + _SIN(ind),
+              xe = circle_x + _COS(ind + 1),
+              ye = circle_y + _SIN(ind + 1);
 
-        float rx = circle_x + cos_table[tmp_div_30],    // for speed, these are now a lookup table entry
-              ry = circle_y + sin_table[tmp_div_30],
-              xe = circle_x + cos_table[tmp_div_30 + 1],
-              ye = circle_y + sin_table[tmp_div_30 + 1];
         #if IS_KINEMATIC
           // Check to make sure this segment is entirely on the bed, skip if not.
           if (!position_is_reachable(rx, ry) || !position_is_reachable(xe, ye)) continue;