Wipe tower: Wipe less than usual amount of material if the wipe

is followed by the final sparse zig-zag tower section.

xs/src/libslic3r/GCode/ToolOrdering.cpp

@@ -244,7 +244,7 @@ void ToolOrdering::fill_wipe_tower_partitions()
 
     //FIXME this is a hack to get the ball rolling.
     for (LayerTools &lt : m_layer_tools)
-        lt.has_wipe_tower = lt.has_object;
+        lt.has_wipe_tower = lt.has_object && lt.wipe_tower_partitions > 0;
 }
 
 } // namespace Slic3r

xs/src/libslic3r/GCode/WipeTower.hpp

@@ -92,7 +92,7 @@ public:
 
 	// Returns gcode for toolchange and the end position.
 	// if new_tool == -1, just unload the current filament over the wipe tower.
-	virtual ToolChangeResult tool_change(int new_tool, Purpose purpose = PURPOSE_MOVE_TO_TOWER_AND_EXTRUDE) = 0;
+	virtual ToolChangeResult tool_change(int new_tool, bool last_in_layer, Purpose purpose = PURPOSE_MOVE_TO_TOWER_AND_EXTRUDE) = 0;
 
 	// Close the current wipe tower layer with a perimeter and possibly fill the unfilled space with a zig-zag.
 	// Call this method only if layer_finished() is false.

xs/src/libslic3r/GCode/WipeTowerPrusaMM.cpp

@@ -340,7 +340,7 @@ WipeTowerPrusaMM::material_type WipeTowerPrusaMM::parse_material(const char *nam
 	return INVALID;
 }
 
-WipeTower::ToolChangeResult WipeTowerPrusaMM::tool_change(int tool, Purpose purpose)
+WipeTower::ToolChangeResult WipeTowerPrusaMM::tool_change(int tool, bool last_in_layer, Purpose purpose)
 {
 	// Either it is the last tool unload,
 	// or there must be a nonzero wipe tower partitions available.
@@ -351,10 +351,47 @@ WipeTower::ToolChangeResult WipeTowerPrusaMM::tool_change(int tool, Purpose purp
 		return toolchange_Brim(purpose);
 	}
 
+	float wipe_area = m_wipe_area;
+	if (++ m_idx_tool_change_in_layer < (unsigned int)m_max_color_changes && last_in_layer) {
+		// This tool_change() call will be followed by a finish_layer() call.
+		// Try to shrink the wipe_area to save material, as less than usual wipe is required
+		// if this step is foolowed by finish_layer() extrusions wiping the same extruder.
+		for (size_t iter = 0; iter < 3; ++ iter) {
+			// Simulate the finish_layer() extrusions, summ the length of the extrusion.
+			float e_length = 0.f;
+			{
+				unsigned int old_idx_tool_change = m_idx_tool_change_in_layer;
+			    float old_wipe_start_y = m_current_wipe_start_y;
+			    m_current_wipe_start_y += wipe_area;
+				ToolChangeResult tcr = this->finish_layer(PURPOSE_EXTRUDE);
+				for (size_t i = 1; i < tcr.extrusions.size(); ++ i) {
+					const Extrusion &e = tcr.extrusions[i];
+					if (e.width > 0) {
+						xy v = e.pos - (&e - 1)->pos;
+						e_length += sqrt(v.x*v.x+v.y*v.y);
+					}
+				}
+				m_idx_tool_change_in_layer = old_idx_tool_change;
+				m_current_wipe_start_y = old_wipe_start_y;
+			}
+			// Shrink wipe_area by the amount of extrusion extruded by the finish_layer().
+			// Y stepping of the wipe extrusions.
+			float dy = m_perimeter_width * 0.8f;
+			// Number of whole wipe lines, that would be extruded to wipe as much material as the finish_layer().
+			float num_lines_extruded = floor(e_length / m_wipe_tower_width);
+			// Minimum wipe area is 5mm wide.
+			wipe_area -= num_lines_extruded * dy;
+			if (wipe_area < 5.) {
+				wipe_area = 5.;
+				break;
+			}
+		}
+	}
+
 	box_coordinates cleaning_box(
 		m_wipe_tower_pos + xy(0.f, m_current_wipe_start_y + 0.5f * m_perimeter_width),
 		m_wipe_tower_width, 
-		m_wipe_area - m_perimeter_width);
+		wipe_area - m_perimeter_width);
 
 	PrusaMultiMaterial::Writer writer;
 	writer.set_extrusion_flow(m_extrusion_flow)
@@ -430,8 +467,7 @@ WipeTower::ToolChangeResult WipeTowerPrusaMM::tool_change(int tool, Purpose purp
 					  "\n\n");
 
 	    ++ m_num_tool_changes;
-	    ++ m_idx_tool_change_in_layer;
+	    m_current_wipe_start_y += wipe_area;
-	    m_current_wipe_start_y += m_wipe_area;
 	}
 
 	ToolChangeResult result;
@@ -728,8 +764,8 @@ WipeTower::ToolChangeResult WipeTowerPrusaMM::finish_layer(Purpose purpose)
 	// Slow down on the 1st layer.
 	float speed_factor = m_is_first_layer ? 0.5f : 1.f;
 
-	box_coordinates fill_box(m_wipe_tower_pos + xy(0.f, float(m_idx_tool_change_in_layer) * m_wipe_area),
+	box_coordinates fill_box(m_wipe_tower_pos + xy(0.f, m_current_wipe_start_y),
-		m_wipe_tower_width, float(m_max_color_changes - m_idx_tool_change_in_layer) * m_wipe_area);
+		m_wipe_tower_width, float(m_max_color_changes) * m_wipe_area - m_current_wipe_start_y);
 	fill_box.expand(0.f, - 0.5f * m_perimeter_width);
 	{
 		float firstLayerOffset = 0.f;

xs/src/libslic3r/GCode/WipeTowerPrusaMM.hpp

@@ -117,7 +117,7 @@ public:
 
 	// Returns gcode for a toolchange and a final print head position.
 	// On the first layer, extrude a brim around the future wipe tower first.
-	virtual ToolChangeResult tool_change(int new_tool, Purpose purpose);
+	virtual ToolChangeResult tool_change(int new_tool, bool last_in_layer, Purpose purpose);
 
 	// Close the current wipe tower layer with a perimeter and possibly fill the unfilled space with a zig-zag.
 	// Call this method only if layer_finished() is false.

xs/src/libslic3r/Print.cpp

@@ -1062,7 +1062,7 @@ void Print::_make_wipe_tower()
         std::vector<WipeTower::ToolChangeResult> tool_changes;
         for (unsigned int extruder_id : layer_tools.extruders)
             if ((first_layer && extruder_id == initial_extruder_id) || extruder_id != current_extruder_id) {
-                tool_changes.emplace_back(wipe_tower.tool_change(extruder_id, WipeTower::PURPOSE_EXTRUDE));
+                tool_changes.emplace_back(wipe_tower.tool_change(extruder_id, extruder_id == layer_tools.extruders.back(), WipeTower::PURPOSE_EXTRUDE));
                 current_extruder_id = extruder_id;
             }
         if (! wipe_tower.layer_finished()) {
@@ -1105,7 +1105,7 @@ void Print::_make_wipe_tower()
         wipe_tower.set_layer(float(m_tool_ordering.back().print_z), float(layer_height), 0, false, true);
     }
     m_wipe_tower_final_purge = Slic3r::make_unique<WipeTower::ToolChangeResult>(
-        wipe_tower.tool_change(-1, WipeTower::PURPOSE_EXTRUDE));
+        wipe_tower.tool_change(-1, false, WipeTower::PURPOSE_EXTRUDE));
 }
 
 std::string Print::output_filename()