ENH: modify the start pos of wall for wipe tower[affects BBL machines only] (#8439)

and modify the overlap of wall and infill for wipe tower jira:none

cherry picked from commit
bambulab/BambuStudio@4db196b11f

Thanks BambuLab!

- Optimize the starting position of the printing wiper tower after
material change, the initial print on the wipe tower sometimes had
under-extrusion issues, and all layers of wipe tower have the same
starting position, increasing the risk of collision. This optimization
distributes the initial extrusion over four corners, reducing the
accumulation of defects.
- Reducing the rivet length between the wipe tower's outer wall and
infill to 0mm minimizes the risk of collision when switching between
printing infill and outer walls.


![image](https://github.com/user-attachments/assets/7cd4daf2-4df4-4bfc-b447-99099e73631b)

src/libslic3r/GCode/WipeTower.cpp

@@ -14,6 +14,7 @@
 
 namespace Slic3r
 {
+static const double wipe_tower_wall_infill_overlap = 0.0;
 
 inline float align_round(float value, float base)
 {
@@ -802,12 +803,30 @@ WipeTower::ToolChangeResult WipeTower::tool_change(size_t tool, bool extrude_per
             box_coordinates wt_box(Vec2f(0.f, (m_current_shape == SHAPE_REVERSED) ? m_layer_info->toolchanges_depth() - m_layer_info->depth : 0.f),
                 m_wipe_tower_width, m_layer_info->depth + m_perimeter_width);
             // align the perimeter
+
+            Vec2f pos = initial_position;
+            switch (m_cur_layer_id % 4){
+            case 0:
+                pos = wt_box.ld;
+                break;
+            case 1:
+                pos = wt_box.rd;
+                break;
+            case 2:
+                pos = wt_box.ru;
+                break;
+            case 3:
+                pos = wt_box.lu;
+                break;
+            default: break;
+            }
+            writer.set_initial_position(pos, m_wipe_tower_width, m_wipe_tower_depth, m_internal_rotation);
+
             wt_box = align_perimeter(wt_box);
             writer.rectangle(wt_box);
-            writer.travel(initial_position);
         }
 
-        if (first_toolchange_to_nonsoluble) {
+        {
             writer.travel(Vec2f(0, 0));
             writer.travel(initial_position);
         }
@@ -1108,9 +1127,9 @@ void WipeTower::toolchange_Wipe(
         }
 
         if (m_left_to_right)
-            writer.extrude(xr + 0.25f * m_perimeter_width, writer.y(), wipe_speed);
+            writer.extrude(xr + wipe_tower_wall_infill_overlap * m_perimeter_width, writer.y(), wipe_speed);
         else
-            writer.extrude(xl - 0.25f * m_perimeter_width, writer.y(), wipe_speed);
+            writer.extrude(xl - wipe_tower_wall_infill_overlap * m_perimeter_width, writer.y(), wipe_speed);
 
         // BBS: recover the flow in non-bridging area
         if (need_change_flow) {
@@ -1600,10 +1619,11 @@ void WipeTower::generate(std::vector<std::vector<WipeTower::ToolChangeResult>> &
         used = 0.f;
 
     m_old_temperature = -1; // reset last temperature written in the gcode
-
+    int index = 0;
     std::vector<WipeTower::ToolChangeResult> layer_result;
 	for (auto layer : m_plan)
 	{
+        m_cur_layer_id = index++;
         set_layer(layer.z, layer.height, 0, false/*layer.z == m_plan.front().z*/, layer.z == m_plan.back().z);
         // BBS
         //m_internal_rotation += 180.f;

src/libslic3r/GCode/WipeTower.hpp

@@ -304,7 +304,7 @@ private:
     float  m_travel_speed       = 0.f;
     float  m_first_layer_speed  = 0.f;
     size_t m_first_layer_idx    = size_t(-1);
-
+    size_t m_cur_layer_id;
 	// G-code generator parameters.
     float           m_cooling_tube_retraction   = 0.f;
     float           m_cooling_tube_length       = 0.f;