Fix overflow in distance_to(Line*). It was affecting Douglas-Peucker causing massive loss of geometry. Includes regression test and a couple wkt() implementations

xs/src/Line.cpp

@@ -1,9 +1,19 @@
 #include "Line.hpp"
 #include "Polyline.hpp"
 #include <algorithm>
+#include <sstream>
 
 namespace Slic3r {
 
+std::string
+Line::wkt() const
+{
+    std::ostringstream ss;
+    ss << "LINESTRING(" << this->a.x << " " << this->a.y << ","
+        << this->b.x << " " << this->b.y << ")";
+    return ss.str();
+}
+
 Line::operator Polyline() const
 {
     Polyline pl;

xs/src/Line.hpp

@@ -16,6 +16,7 @@ class Line
     Point b;
     Line() {};
     explicit Line(Point _a, Point _b): a(_a), b(_b) {};
+    std::string wkt() const;
     operator Polyline() const;
     void scale(double factor);
     void translate(double x, double y);

xs/src/Point.cpp

@@ -1,9 +1,18 @@
 #include "Point.hpp"
 #include "Line.hpp"
 #include <cmath>
+#include <sstream>
 
 namespace Slic3r {
 
+std::string
+Point::wkt() const
+{
+    std::ostringstream ss;
+    ss << "POINT(" << this->x << " " << this->y << ")";
+    return ss.str();
+}
+
 void
 Point::scale(double factor)
 {
@@ -100,8 +109,8 @@ Point::distance_to(const Line &line) const
 {
     if (line.a.coincides_with(&line.b)) return this->distance_to(&line.a);
     
-    double n = (line.b.x - line.a.x) * (line.a.y - this->y)
-        - (line.a.x - this->x) * (line.b.y - line.a.y);
+    double n = (double)(line.b.x - line.a.x) * (double)(line.a.y - this->y)
+        - (double)(line.a.x - this->x) * (double)(line.b.y - line.a.y);
     
     return std::abs(n) / line.length();
 }

xs/src/Point.hpp

@@ -4,6 +4,7 @@
 #include <myinit.h>
 #include <vector>
 #include <math.h>
+#include <string>
 
 namespace Slic3r {
 
@@ -20,6 +21,7 @@ class Point
     coord_t x;
     coord_t y;
     explicit Point(coord_t _x = 0, coord_t _y = 0): x(_x), y(_y) {};
+    std::string wkt() const;
     void scale(double factor);
     void translate(double x, double y);
     void rotate(double angle, Point* center);