New +Line::intersection_infinite() method

xs/src/libslic3r/Line.cpp

@@ -89,6 +89,23 @@ Line::point_at(double distance) const
     return p;
 }
 
+bool
+Line::intersection_infinite(const Line &other, Point* point) const
+{
+    Vector x = this->a.vector_to(other.a);
+    Vector d1 = this->vector();
+    Vector d2 = other.vector();
+
+    double cross = d1.x * d2.y - d1.y * d2.x;
+    if (std::fabs(cross) < EPSILON)
+        return false;
+
+    double t1 = (x.x * d2.y - x.y * d2.x)/cross;
+    point->x = this->a.x + d1.x * t1;
+    point->y = this->a.y + d1.y * t1;
+    return true;
+}
+
 bool
 Line::coincides_with(const Line &line) const
 {

xs/src/libslic3r/Line.hpp

@@ -29,6 +29,7 @@ class Line
     Point* midpoint() const;
     void point_at(double distance, Point* point) const;
     Point point_at(double distance) const;
+    bool intersection_infinite(const Line &other, Point* point) const;
     bool coincides_with(const Line &line) const;
     double distance_to(const Point &point) const;
     bool parallel_to(double angle) const;

xs/t/10_line.t

@@ -4,7 +4,7 @@ use strict;
 use warnings;
 
 use Slic3r::XS;
-use Test::More tests => 39;
+use Test::More tests => 40;
 
 use constant PI         => 4 * atan2(1, 1);
 use constant EPSILON    => 1E-4;
@@ -71,4 +71,11 @@ foreach my $base_angle (0, PI/4, PI/2, PI) {
     }
 }
 
+{
+    my $a = Slic3r::Line->new([100, 0], [200, 0]);
+    my $b = Slic3r::Line->new([300, 300], [300, 100]);
+    my $r = $a->intersection_infinite($b);
+    is_deeply $r->pp, [300, 0], 'intersection_infinite';
+}
+
 __END__

xs/xsp/Line.xsp

@@ -30,6 +30,13 @@
         %code{% RETVAL = THIS->parallel_to(*line); %};
     Point* midpoint();
     Clone<Point> point_at(double distance);
+    Clone<Point> intersection_infinite(Line* other)
+        %code{%
+            Point p;
+            bool res = THIS->intersection_infinite(*other, &p);
+            if (!res) CONFESS("Intersection failed");
+            RETVAL = p;
+        %};
     Polyline* as_polyline()
         %code{% RETVAL = new Polyline(*THIS); %};
     Clone<Point> normal();