add configuration check for virtual endstops, add default for bed pro…

…bing site from bed mesh

README.md

@@ -9,9 +9,15 @@ together do **not** affect the first layer at all.
 
 Here is a small video demonstration: [https://streamable.com/wclrmc](https://streamable.com/wclrmc)
 
-> **NEW:** The probing repeatability is now increased dramatically by using the probing
-> procedure instead of the homing procedure! But note, the offset will change slightly,
-> if Z is homed again or temperatures changes - but this is as intended.
+## New
+
+- **v0.4**: The bed probing point can be omitted and the `relative_reference_index` of
+  the bed mesh is taken as default instead.
+- **v0.3**: A new option to first probe down fast before recording the probing samples.
+  And all indirect properties from other sections can be customized now.
+- **v0.2**: The probing repeatability is now increased dramatically by using the probing
+  procedure instead of the homing procedure! But note, the offset will change slightly,
+  if Z is homed again or temperatures changes - but this is as intended!
 
 ## Why this
 
@@ -113,11 +119,14 @@ probe_switch_x:
 probe_switch_y:
 #   The X and Y coordinates (in mm) for clicking the probe's switch
 #   on the Z endstop.
-probe_bed_x:
-probe_bed_y:
+probe_bed_x: default from relative_reference_index of bed_mesh
+probe_bed_y: default from relative_reference_index of bed_mesh
 #   The X and Y coordinates (in mm) for probing on the print surface
 #   (e.g. the center point) These coordinates will be adapted by the
-#   probe's X and Y offsets.
+#   probe's X and Y offsets. The default is the relative_reference_index
+#   of the configured bed_mesh. It will raise an error if there is no
+#   probe_bed site and no bed_mesh with a relative_reference_index
+#   configured.
 switch_offset:
 #   The trigger point offset of the used mag-probe switch.
 #   This needs to be fined out manually. More on this later
@@ -167,8 +176,10 @@ probing_first_fast: false
 ```
 
 **CAUTION: If you use a bed mesh, the coordinates for probing on the print bed must be
-exaclty the reference point of the mesh since this is the zero point - otherwise, you would
-get into trouble!**
+exactly the relative reference point of the mesh since this is the zero point! In this
+case, you can ommit these properties and as default the relative reference point of the
+mesh will be taken automatically (the `relative_reference_index` of the `bed_mesh` is
+required for this)!**
 
 The `switch_offset` is the already mentioned offset from the switch body (which is the
 probed position) to the actual trigger point. A starting point can be taken from the

z_calibration.py

@@ -1,4 +1,5 @@
 import logging
+from mcu import MCU_endstop
 
 class ZCalibrationHelper:
     def __init__(self, config):
@@ -36,8 +37,8 @@ def __init__(self, config):
             None,
         ]
         self.probe_bed_site = [
-            config.getfloat('probe_bed_x'),
-            config.getfloat('probe_bed_y'),
+            config.getfloat('probe_bed_x', None),
+            config.getfloat('probe_bed_y', None),
             None,
         ]
 
@@ -59,9 +60,15 @@ def handle_connect(self):
         # get z-endstop
         for endstop, name in self.query_endstops.endstops:
             if name == 'z':
+                # check for virtual endstops..
+                if not isinstance(endstop, MCU_endstop):
+                    raise self.printer.config_error(
+                        "No virtual endstops for z are supported for calibrate_z module!")
                 self.z_endstop = EndstopWrapper(self.config, endstop)
         # get probing settings
-        probe = self.printer.lookup_object('probe')
+        probe = self.printer.lookup_object('probe', default=None)
+        if probe is None:
+            raise self.printer.config_error("A configured probe is needed for calibrate_z module!")
         if self.probing_samples is None:
             self.probing_samples = probe.sample_count
         if self.probing_samples_tolerance is None:
@@ -74,6 +81,18 @@ def handle_connect(self):
             self.probing_clearance = probe.z_offset * 2
         if self.probing_samples_result is None:
             self.probing_samples_result = probe.samples_result
+        # get the mesh's relative reference point
+        if self.probe_bed_site[0] is None or self.probe_bed_site[1] is None:
+            mesh = self.printer.lookup_object('bed_mesh', default=None)
+            if mesh is None or mesh.bmc.relative_reference_index is None:
+                raise self.printer.config_error(
+                    "Either configure probe_bed_x and probe_bed_y or configure "
+                    "a mesh with a relative_reference_index for calibrate_z module!")
+            rri = mesh.bmc.relative_reference_index
+            self.probe_bed_site[0] = mesh.bmc.points[rri][0]
+            self.probe_bed_site[1] = mesh.bmc.points[rri][1]
+        logging.debug("Z-CALIBRATION probe_bed_x=%.3f probe_bed_y=%.3f"
+            % (self.probe_bed_site[0], self.probe_bed_site[1]))
 
     def handle_home_rails_end(self, homing_state, rails):
         # get z homing position