Suppor of "No extrusion" firmware flavor by not emitting the E axis.

Fix of https://github.com/prusa3d/PrusaSlicer/issues/6023
The fix is partial: No extrusions are shown by the final G-code preview.

src/libslic3r/GCode.cpp

@@ -2714,7 +2714,9 @@ std::string GCode::_extrude(const ExtrusionPath &path, std::string description,
 
     // calculate extrusion length per distance unit
     double e_per_mm = m_writer.extruder()->e_per_mm3() * path.mm3_per_mm;
-    if (m_writer.extrusion_axis().empty()) e_per_mm = 0;
+    if (m_writer.extrusion_axis().empty())
+        // gcfNoExtrusion
+        e_per_mm = 0;
 
     // set speed
     if (speed == -1) {

src/libslic3r/GCodeReader.cpp

@@ -12,16 +12,24 @@
 
 namespace Slic3r {
 
+static inline char get_extrusion_axis_char(const GCodeConfig &config)
+{
+    std::string axis = get_extrusion_axis(config);
+    assert(axis.size() <= 1);
+    // Return 0 for gcfNoExtrusion
+    return axis.empty() ? 0 : axis[0];
+}
+
 void GCodeReader::apply_config(const GCodeConfig &config)
 {
     m_config = config;
-    m_extrusion_axis = get_extrusion_axis(m_config)[0];
+    m_extrusion_axis = get_extrusion_axis_char(m_config);
 }
 
 void GCodeReader::apply_config(const DynamicPrintConfig &config)
 {
     m_config.apply(config, true);
-    m_extrusion_axis = get_extrusion_axis(m_config)[0];
+    m_extrusion_axis = get_extrusion_axis_char(m_config);
 }
 
 const char* GCodeReader::parse_line_internal(const char *ptr, GCodeLine &gline, std::pair<const char*, const char*> &command)
@@ -52,9 +60,10 @@ const char* GCodeReader::parse_line_internal(const char *ptr, GCodeLine &gline,
             case 'Z': axis = Z; break;
             case 'F': axis = F; break;
             default:
-                if (*c == m_extrusion_axis)
-                    axis = E;
-                else if (*c >= 'A' && *c <= 'Z')
+                if (*c == m_extrusion_axis) {
+                    if (m_extrusion_axis != 0)
+                        axis = E;
+                } else if (*c >= 'A' && *c <= 'Z')
                 	// Unknown axis, but we still want to remember that such a axis was seen.
                 	axis = UNKNOWN_AXIS;
                 break;
@@ -190,6 +199,8 @@ void GCodeReader::GCodeLine::set(const GCodeReader &reader, const Axis axis, con
         match[1] = 'F';
     else {
         assert(axis == E);
+        // Extruder axis is set.
+        assert(reader.extrusion_axis() != 0);
         match[1] = reader.extrusion_axis();
     }
 

src/libslic3r/GCodeReader.hpp

@@ -122,8 +122,9 @@ public:
     float& f()       { return m_position[F]; }
     float  f() const { return m_position[F]; }
 
+    // Returns 0 for gcfNoExtrusion.
     char   extrusion_axis() const { return m_extrusion_axis; }
-    void   set_extrusion_axis(char axis) { m_extrusion_axis = axis; }
+//  void   set_extrusion_axis(char axis) { m_extrusion_axis = axis; }
 
 private:
     const char* parse_line_internal(const char *ptr, GCodeLine &gline, std::pair<const char*, const char*> &command);

src/libslic3r/GCodeWriter.cpp

@@ -405,8 +405,10 @@ std::string GCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std:
     
     std::ostringstream gcode;
     gcode << "G1 X" << XYZF_NUM(point(0))
-          <<   " Y" << XYZF_NUM(point(1))
-          <<    " " << m_extrusion_axis << E_NUM(m_extruder->E());
+          <<   " Y" << XYZF_NUM(point(1));
+    if (! m_extrusion_axis.empty())
+        // not gcfNoExtrusion
+        gcode << " " << m_extrusion_axis << E_NUM(m_extruder->E());
     COMMENT(comment);
     gcode << "\n";
     return gcode.str();
@@ -421,8 +423,10 @@ std::string GCodeWriter::extrude_to_xyz(const Vec3d &point, double dE, const std
     std::ostringstream gcode;
     gcode << "G1 X" << XYZF_NUM(point(0))
           <<   " Y" << XYZF_NUM(point(1))
-          <<   " Z" << XYZF_NUM(point(2))
-          <<    " " << m_extrusion_axis << E_NUM(m_extruder->E());
+          <<   " Z" << XYZF_NUM(point(2));
+    if (! m_extrusion_axis.empty())
+        // not gcfNoExtrusion
+        gcode << " " << m_extrusion_axis << E_NUM(m_extruder->E());
     COMMENT(comment);
     gcode << "\n";
     return gcode.str();
@@ -474,7 +478,7 @@ std::string GCodeWriter::_retract(double length, double restart_extra, const std
                 gcode << "G22 ; retract\n";
             else
                 gcode << "G10 ; retract\n";
-        } else {
+        } else if (! m_extrusion_axis.empty()) {
             gcode << "G1 " << m_extrusion_axis << E_NUM(m_extruder->E())
                            << " F" << XYZF_NUM(m_extruder->retract_speed() * 60.);
             COMMENT(comment);
@@ -503,7 +507,7 @@ std::string GCodeWriter::unretract()
             else
                  gcode << "G11 ; unretract\n";
             gcode << this->reset_e();
-        } else {
+        } else if (! m_extrusion_axis.empty()) {
             // use G1 instead of G0 because G0 will blend the restart with the previous travel move
             gcode << "G1 " << m_extrusion_axis << E_NUM(m_extruder->E())
                            << " F" << XYZF_NUM(m_extruder->deretract_speed() * 60.);

src/libslic3r/GCodeWriter.hpp

@@ -25,6 +25,7 @@ public:
     Extruder*            extruder()             { return m_extruder; }
     const Extruder*      extruder()     const   { return m_extruder; }
 
+    // Returns empty string for gcfNoExtrusion.
     std::string          extrusion_axis() const { return m_extrusion_axis; }
     void                 apply_print_config(const PrintConfig &print_config);
     // Extruders are expected to be sorted in an increasing order.