Renamed Line::offset to extend

Don't use unscaled constants! What if the scaling constant changes
in the future?

src/libslic3r/Fill/FillAdaptive.cpp

@@ -625,7 +625,7 @@ static Line create_offset_line(const Line &line_to_offset, const Intersection &i
     Line  offset_line    = line_to_offset;
     offset_line.translate(offset_vector.x(), offset_vector.y());
     // Extend the line by small value to guarantee a collision with adjacent lines
-    offset_line.offset(1000000);
+    offset_line.extend(coord_t(scale_(1.)));
     return offset_line;
 };
 

src/libslic3r/Line.cpp

@@ -100,7 +100,7 @@ bool Line::clip_with_bbox(const BoundingBox &bbox)
 	return result;
 }
 
-void Line::offset(double offset)
+void Line::extend(double offset)
 {
     Vector offset_vector = (offset * this->vector().cast<double>().normalized()).cast<coord_t>();
     this->a -= offset_vector;

src/libslic3r/Line.hpp

@@ -75,8 +75,8 @@ public:
     double ccw(const Point& point) const { return point.ccw(*this); }
     // Clip a line with a bounding box. Returns false if the line is completely outside of the bounding box.
 	bool   clip_with_bbox(const BoundingBox &bbox);
-    // Resize a line from both sides by the offset.
-    void   offset(double offset);
+    // Extend the line from both sides by an offset.
+    void   extend(double offset);
 
     static inline double distance_to_squared(const Point &point, const Point &a, const Point &b) { return line_alg::distance_to_squared(Line{a, b}, Vec<2, coord_t>{point}); }
     static double distance_to(const Point &point, const Point &a, const Point &b) { return sqrt(distance_to_squared(point, a, b)); }