Ported remove_collinear(Polygon) and test_polygon from upstream slic3r.

src/libslic3r/GCode/CoolingBuffer.hpp

@@ -1,7 +1,7 @@
 #ifndef slic3r_CoolingBuffer_hpp_
 #define slic3r_CoolingBuffer_hpp_
 
-#include "libslic3r.h"
+#include "../libslic3r.h"
 #include <map>
 #include <string>
 

src/libslic3r/Polygon.cpp

@@ -15,7 +15,7 @@ Polyline Polygon::split_at_vertex(const Point &point) const
     // find index of point
     for (const Point &pt : this->points)
         if (pt == point)
-            return this->split_at_index(&pt - &this->points.front());
+            return this->split_at_index(int(&pt - &this->points.front()));
     throw std::invalid_argument("Point not found");
     return Polyline();
 }
@@ -394,4 +394,45 @@ bool remove_small(Polygons &polys, double min_area)
     return modified;
 }
 
+void remove_collinear(Polygon &poly)
+{
+    if (poly.points.size() > 2) {
+        // copy points and append both 1 and last point in place to cover the boundaries
+        Points pp;
+        pp.reserve(poly.points.size()+2);
+        pp.push_back(poly.points.back());
+        pp.insert(pp.begin()+1, poly.points.begin(), poly.points.end());
+        pp.push_back(poly.points.front());
+        // delete old points vector. Will be re-filled in the loop
+        poly.points.clear();
+
+        size_t i = 0;
+        size_t k = 0;
+        while (i < pp.size()-2) {
+            k = i+1;
+            const Point &p1 = pp[i];
+            while (k < pp.size()-1) {
+                const Point &p2 = pp[k];
+                const Point &p3 = pp[k+1];
+                Line l(p1, p3);
+                if(l.distance_to(p2) < SCALED_EPSILON) {
+                    k++;
+                } else {
+                    if(i > 0) poly.points.push_back(p1); // implicitly removes the first point we appended above
+                    i = k;
+                    break;
+                }
+            }
+            if(k > pp.size()-2) break; // all remaining points are collinear and can be skipped
+        }
+        poly.points.push_back(pp[i]);
+    }
+}
+
+void remove_collinear(Polygons &polys)
+{
+	for (Polygon &poly : polys)
+		remove_collinear(poly);
+}
+
 }

src/libslic3r/Polygon.hpp

@@ -86,6 +86,8 @@ extern bool        remove_sticks(Polygons &polys);
 // Remove polygons with less than 3 edges.
 extern bool        remove_degenerate(Polygons &polys);
 extern bool        remove_small(Polygons &polys, double min_area);
+extern void 	   remove_collinear(Polygon &poly);
+extern void 	   remove_collinear(Polygons &polys);
 
 // Append a vector of polygons at the end of another vector of polygons.
 inline void        polygons_append(Polygons &dst, const Polygons &src) { dst.insert(dst.end(), src.begin(), src.end()); }

tests/libslic3r/CMakeLists.txt

@@ -2,6 +2,7 @@ get_filename_component(_TEST_NAME ${CMAKE_CURRENT_LIST_DIR} NAME)
 add_executable(${_TEST_NAME}_tests 
 	${_TEST_NAME}_tests.cpp
 	test_geometry.cpp
+	test_polygon.cpp
 	)
 target_link_libraries(${_TEST_NAME}_tests test_common libslic3r)
 set_property(TARGET ${_TEST_NAME}_tests PROPERTY FOLDER "tests")

tests/libslic3r/test_polygon.cpp

@@ -0,0 +1,44 @@
+#include <catch2/catch.hpp>
+
+#include "libslic3r/Point.hpp"
+#include "libslic3r/Polygon.hpp"
+
+using namespace Slic3r;
+
+// This test currently only covers remove_collinear_points.
+// All remaining tests are to be ported from xs/t/06_polygon.t
+
+Slic3r::Points collinear_circle({
+    Slic3r::Point::new_scale(0, 0), // 3 collinear points at beginning
+    Slic3r::Point::new_scale(10, 0),
+    Slic3r::Point::new_scale(20, 0),
+    Slic3r::Point::new_scale(30, 10),
+    Slic3r::Point::new_scale(40, 20), // 2 collinear points
+    Slic3r::Point::new_scale(40, 30),
+    Slic3r::Point::new_scale(30, 40), // 3 collinear points
+    Slic3r::Point::new_scale(20, 40),
+    Slic3r::Point::new_scale(10, 40),
+    Slic3r::Point::new_scale(-10, 20),
+    Slic3r::Point::new_scale(-20, 10),
+    Slic3r::Point::new_scale(-20, 0), // 3 collinear points at end
+    Slic3r::Point::new_scale(-10, 0),
+    Slic3r::Point::new_scale(-5, 0)
+});
+
+SCENARIO("Remove collinear points from Polygon") {
+    GIVEN("Polygon with collinear points"){
+        Slic3r::Polygon p(collinear_circle);
+        WHEN("collinear points are removed") {
+            remove_collinear(p);
+            THEN("Leading collinear points are removed") {
+                REQUIRE(p.points.front() == Slic3r::Point::new_scale(20, 0));
+            }
+            THEN("Trailing collinear points are removed") {
+                REQUIRE(p.points.back() == Slic3r::Point::new_scale(-20, 0));
+            }
+            THEN("Number of remaining points is correct") {
+                REQUIRE(p.points.size() == 7);
+            }
+        }
+    }
+}