ExtruderSequenceDialog :

Fixed layouts after the second opening of the dialog.
 (Removing any extruder from the sequence does not cause an incorrect layout)
Validation of entered values added
 (0 is not a valid value)

src/libslic3r/GCode/ThumbnailData.cpp

@@ -0,0 +1,36 @@
+#include "libslic3r/libslic3r.h"
+#include "ThumbnailData.hpp"
+
+#if ENABLE_THUMBNAIL_GENERATOR
+
+namespace Slic3r {
+
+void ThumbnailData::set(unsigned int w, unsigned int h)
+{
+    if ((w == 0) || (h == 0))
+        return;
+
+    if ((width != w) || (height != h))
+    {
+        width = w;
+        height = h;
+        // defaults to white texture
+        pixels = std::vector<unsigned char>(width * height * 4, 255);
+    }
+}
+
+void ThumbnailData::reset()
+{
+    width = 0;
+    height = 0;
+    pixels.clear();
+}
+
+bool ThumbnailData::is_valid() const
+{
+    return (width != 0) && (height != 0) && ((unsigned int)pixels.size() == 4 * width * height);
+}
+
+} // namespace Slic3r
+
+#endif // ENABLE_THUMBNAIL_GENERATOR

src/libslic3r/GCode/ThumbnailData.hpp

@@ -0,0 +1,27 @@
+#ifndef slic3r_ThumbnailData_hpp_
+#define slic3r_ThumbnailData_hpp_
+
+#if ENABLE_THUMBNAIL_GENERATOR
+
+#include <vector>
+
+namespace Slic3r {
+
+struct ThumbnailData
+{
+    unsigned int width;
+    unsigned int height;
+    std::vector<unsigned char> pixels;
+
+    ThumbnailData() { reset(); }
+    void set(unsigned int w, unsigned int h);
+    void reset();
+
+    bool is_valid() const;
+};
+
+} // namespace Slic3r
+
+#endif // ENABLE_THUMBNAIL_GENERATOR
+
+#endif // slic3r_ThumbnailData_hpp_

src/libslic3r/GCode/WipeTower.cpp

@@ -474,6 +474,7 @@ WipeTower::WipeTower(const PrintConfig& config, const std::vector<std::vector<fl
     m_z_pos(0.f),
     m_is_first_layer(false),
     m_bridging(float(config.wipe_tower_bridging)),
+    m_no_sparse_layers(config.wipe_tower_no_sparse_layers),
     m_gcode_flavor(config.gcode_flavor),
     m_current_tool(initial_tool),
     wipe_volumes(wiping_matrix)
@@ -1145,9 +1146,10 @@ WipeTower::ToolChangeResult WipeTower::finish_layer()
     writer.set_initial_position((m_left_to_right ? fill_box.ru : fill_box.lu), // so there is never a diagonal travel
                                  m_wipe_tower_width, m_wipe_tower_depth, m_internal_rotation);
 
+    bool toolchanges_on_layer = m_layer_info->toolchanges_depth() > WT_EPSILON;
 	box_coordinates box = fill_box;
     for (int i=0;i<2;++i) {
-        if (m_layer_info->toolchanges_depth() < WT_EPSILON) { // there were no toolchanges on this layer
+        if (! toolchanges_on_layer) {
             if (i==0) box.expand(m_perimeter_width);
             else box.expand(-m_perimeter_width);
         }
@@ -1201,9 +1203,12 @@ WipeTower::ToolChangeResult WipeTower::finish_layer()
 
     m_depth_traversed = m_wipe_tower_depth-m_perimeter_width;
 
-    // Ask our writer about how much material was consumed:
-    if (m_current_tool < m_used_filament_length.size())
-        m_used_filament_length[m_current_tool] += writer.get_and_reset_used_filament_length();
+
+    // Ask our writer about how much material was consumed.
+    // Skip this in case the layer is sparse and config option to not print sparse layers is enabled.
+    if (! m_no_sparse_layers || toolchanges_on_layer)
+        if (m_current_tool < m_used_filament_length.size())
+            m_used_filament_length[m_current_tool] += writer.get_and_reset_used_filament_length();
 
     ToolChangeResult result;
     result.priming      = false;

src/libslic3r/GCode/WipeTower.hpp

@@ -220,6 +220,7 @@ private:
     float           m_parking_pos_retraction    = 0.f;
     float           m_extra_loading_move        = 0.f;
     float           m_bridging                  = 0.f;
+    bool            m_no_sparse_layers          = false;
     bool            m_set_extruder_trimpot      = false;
     bool            m_adhesion                  = true;
     GCodeFlavor     m_gcode_flavor;