Add unretraction parameter to G26

G26 Gcode:
- Change Q parameter to only specify retraction length
- Add Z parameter for unretraction length
- Preserve fixed multiplier of 1.2 if Z isn't specified
- Add check to avoid implausible retract/unretract ratios
- Change default config values

Referencing #31. Thanks to @BlackMulch for the feedback!

Marlin/G26_Mesh_Validation_Tool.cpp

@@ -44,8 +44,9 @@
   #endif
 
   #define EXTRUSION_MULTIPLIER 1.0
-  #define RETRACTION_MULTIPLIER 6
-  #define PRIME_LENGTH 25.0
+  #define RETRACTION_LENGTH 1
+  #define UNRETRACTION_LENGTH 1.2
+  #define PRIME_LENGTH 5
   #define OOZE_AMOUNT 2.25
 
   #define INTERSECTION_CIRCLE_RADIUS 5
@@ -107,8 +108,9 @@
    *                    pliers while holding the LCD Click wheel in a depressed state. If you do not have
    *                    an LCD, you must specify a value if you use P.
    *
-   *   Q #  Multiplier  Retraction Multiplier. Normally not needed. Retraction defaults to 1.0mm and
-   *                    un-retraction is at 1.2mm   These numbers will be scaled by the specified amount
+   *   Q #  Retract     Retraction length. Defaults to 1mm if not specified.
+   *   Z #  Unretract   Unretraction length. Defaults to 1.2mm if not specified.
+   *                    Note: If Q is specified but Z isn't, Z defaults to Q * 1.2.
    *
    *   R #  Repeat      Prints the number of patterns given as a parameter, starting at the current location.
    *                    If a parameter isn't given, every point will be printed unless G26 is interrupted.
@@ -145,7 +147,8 @@
                                      // retracts/recovers won't result in a bad state.
 
   static float g26_extrusion_multiplier,
-               g26_retraction_multiplier,
+               g26_retraction_length,
+               g26_unretraction_length,
                g26_layer_height,
                g26_prime_length,
                g26_x_pos, g26_y_pos;
@@ -223,13 +226,13 @@
   void retract_filament(const float where[XYZE]) {
     if (!g26_retracted) { // Only retract if we are not already retracted!
       g26_retracted = true;
-      move_to(where, -1.0 * g26_retraction_multiplier);
+      move_to(where, -1.0 * g26_retraction_length);
     }
   }
 
   void recover_filament(const float where[XYZE]) {
     if (g26_retracted) { // Only un-retract if we are retracted.
-      move_to(where, 1.2 * g26_retraction_multiplier);
+      move_to(where, g26_unretraction_length);
       g26_retracted = false;
     }
   }
@@ -564,7 +567,8 @@
     if (axis_unhomed_error()) return;
 
     g26_extrusion_multiplier    = EXTRUSION_MULTIPLIER;
-    g26_retraction_multiplier   = RETRACTION_MULTIPLIER;
+    g26_retraction_length       = RETRACTION_LENGTH;
+    g26_unretraction_length     = UNRETRACTION_LENGTH;
     g26_layer_height            = MESH_TEST_LAYER_HEIGHT;
     g26_prime_length            = PRIME_LENGTH;
     g26_bed_temp                = MESH_TEST_BED_TEMP;
@@ -596,14 +600,44 @@
 
     if (parser.seen('Q')) {
       if (parser.has_value()) {
-        g26_retraction_multiplier = parser.value_float();
-        if (!WITHIN(g26_retraction_multiplier, 0.05, 15.0)) {
-          SERIAL_PROTOCOLLNPGM("?Specified Retraction Multiplier not plausible.");
+        g26_retraction_length = parser.value_float();
+        if (!WITHIN(g26_retraction_length, 0.05, 15.0)) {
+          SERIAL_PROTOCOLLNPGM("?Specified Retraction length not plausible.");
           return;
         }
       }
       else {
-        SERIAL_PROTOCOLLNPGM("?Retraction Multiplier must be specified.");
+        SERIAL_PROTOCOLLNPGM("?Retraction length must be specified.");
+        return;
+      }
+    }
+
+    if (parser.seen('Z')) {
+      if (parser.has_value()) {
+        g26_unretraction_length = parser.value_float();
+        if (!WITHIN(g26_unretraction_length, 0.05, 15.0)) {
+          SERIAL_PROTOCOLLNPGM("?Specified Unretraction length not plausible.");
+          return;
+        }
+      }
+      else {
+        SERIAL_PROTOCOLLNPGM("?Unretraction length must be specified.");
+        return;
+      }
+    }
+
+    if (!parser.seen('Z') && parser.seen('Q')) {
+      // retraction without unretraction specified, use 1.2 multiplier (preserve Gcode spec)
+      g26_unretraction_length = g26_retraction_length * 1.2;
+      SERIAL_ECHOPAIR(" Unretraction amount automatically set to ", g26_unretraction_length);
+      SERIAL_EOL();
+    }
+
+    if (parser.seen('Z') && parser.seen('Q')) {
+      // consider typos or unreasonable retract/unretract ratios
+      float g26_retract_unretract_delta = g26_unretraction_length - g26_retraction_length;
+      if (!WITHIN(g26_retract_unretract_delta, -5, 5)) {
+        SERIAL_PROTOCOLLNPGM("?Invalid Retraction/Unretraction ratio. Must be within 5mm.");
         return;
       }
     }

Marlin/Version.h

@@ -41,7 +41,7 @@
    * Defines the version of the Marlin-AI3M build. Not to be confused with
    * Marlin's own build number, e.g. 1.1.9.
    */
-  #define CUSTOM_BUILD_VERSION "v1.4.4"
+  #define CUSTOM_BUILD_VERSION "v1.4.5"
 
   /**
    * Verbose version identifier which should contain a reference to the location
@@ -54,7 +54,7 @@
    * here we define this default string as the date where the latest release
    * version was tagged.
    */
-  #define STRING_DISTRIBUTION_DATE "2019-03-13"
+  #define STRING_DISTRIBUTION_DATE "2019-03-24"
 
   /**
    * Required minimum Configuration.h and Configuration_adv.h file versions.