option to control layer height gradation for adaptive slicing

lib/Slic3r/GUI/Tab.pm

@@ -455,7 +455,7 @@ sub build {
     my $self = shift;
     
     $self->init_config_options(qw(
-    	adaptive_slicing cusp_value match_horizontal_surfaces
+    	adaptive_slicing adaptive_slicing_z_gradation cusp_value match_horizontal_surfaces
         layer_height first_layer_height
         perimeters spiral_vase
         top_solid_layers bottom_solid_layers
@@ -504,6 +504,7 @@ sub build {
             $optgroup->append_single_option_line('first_layer_height');
             $optgroup->append_single_option_line('adaptive_slicing');
             $optgroup->append_single_option_line('cusp_value');
+            $optgroup->append_single_option_line('adaptive_slicing_z_gradation');
             $optgroup->append_single_option_line('match_horizontal_surfaces');
         }
         {
@@ -790,7 +791,7 @@ sub _update {
 
     my $have_adaptive_slicing = $config->adaptive_slicing;
     $self->get_field($_)->toggle($have_adaptive_slicing)
-        for qw(cusp_value match_horizontal_surfaces);
+        for qw(cusp_value adaptive_slicing_z_gradation match_horizontal_surfaces);
     $self->get_field($_)->toggle(!$have_adaptive_slicing)
         for qw(layer_height);
     

lib/Slic3r/Print/Object.pm

@@ -163,6 +163,12 @@ sub slice {
 			       	$height = ($id == 0)
                 		? $self->config->get_value('first_layer_height')
                 		: min($cusp_height, $height);
+                		
+                	# apply z-gradation
+                	my $gradation = $self->config->get_value('adaptive_slicing_z_gradation');
+                	if($gradation > 0) {
+                		$height = $height - unscale((scale($height)) % (scale($gradation)));
+                	}
 		       	}
 
         	}else{

xs/src/libslic3r/PrintConfig.cpp

@@ -14,6 +14,14 @@ PrintConfigDef::PrintConfigDef()
     def->cli = "adaptive-slicing!";
     def->default_value = new ConfigOptionBool(false);
     
+    def = this->add("adaptive_slicing_z_gradation", coFloat);
+	def->label = "Min layer height gradation";
+	def->tooltip = "Limit layer heights to a multiple of this value to avoid stepping inaccuracies at the Z-axis. Typical value for a Prusa i3, 1/16 micro-stepping is 0.004mm. Set zero do disable this option.";
+    def->sidetext = "mm";
+    def->cli = "adaptive-slicing-z-gradation=f";
+    def->min = 0;
+	def->default_value = new ConfigOptionFloat(0);
+
     def = this->add("avoid_crossing_perimeters", coBool);
     def->label = "Avoid crossing perimeters";
     def->tooltip = "Optimize travel moves in order to minimize the crossing of perimeters. This is mostly useful with Bowden extruders which suffer from oozing. This feature slows down both the print and the G-code generation.";

xs/src/libslic3r/PrintConfig.hpp

@@ -104,6 +104,7 @@ class PrintObjectConfig : public virtual StaticPrintConfig
 {
     public:
 	ConfigOptionBool                adaptive_slicing;
+	ConfigOptionFloat               adaptive_slicing_z_gradation;
 	ConfigOptionFloat               cusp_value;
     ConfigOptionBool                dont_support_bridges;
     ConfigOptionFloatOrPercent      extrusion_width;
@@ -137,6 +138,7 @@ class PrintObjectConfig : public virtual StaticPrintConfig
     
     virtual ConfigOption* optptr(const t_config_option_key &opt_key, bool create = false) {
         OPT_PTR(adaptive_slicing);
+        OPT_PTR(adaptive_slicing_z_gradation);
         OPT_PTR(cusp_value);
         OPT_PTR(dont_support_bridges);
         OPT_PTR(extrusion_width);

xs/src/libslic3r/PrintObject.cpp

@@ -228,6 +228,7 @@ PrintObject::invalidate_state_by_config_options(const std::vector<t_config_optio
             || *opt_key == "first_layer_height"
             || *opt_key == "xy_size_compensation"
             || *opt_key == "adaptive_slicing"
+            || *opt_key == "adaptive_slicing_z_gradation"
         	|| *opt_key == "cusp_value"
         	|| *opt_key == "match_horizontal_surfaces"
         	|| *opt_key == "raft_layers") {