Fixed a bug in the hole-aware raycaster

src/libslic3r/SLA/Hollowing.cpp

@@ -223,7 +223,10 @@ bool DrainHole::get_intersections(const Vec3f& s, const Vec3f& dir,
         // they are on the cylinder and not past it:
         for (int i=-1; i<=1 && found !=2; i+=2) {
             Vec3f isect = closest + i*dist * projected_ray.direction();
-            float par = (isect-proj_origin).norm() / par_scale;
+            Vec3f to_isect = isect-proj_origin;
+            float par = to_isect.norm() / par_scale;
+            if (to_isect.normalized().dot(proj_dir.normalized()) < 0.f)
+                par *= -1.f;
             Vec3d hit_normal = (pos-isect).normalized().cast<double>();
             isect = ray.pointAt(par);
             // check that the intersection is between the base planes:

tests/sla_print/sla_raycast_tests.cpp

@@ -8,6 +8,38 @@
 
 using namespace Slic3r;
 
+// First do a simple test of the hole raycaster.
+TEST_CASE("Raycaster - find intersections of a line and cylinder")
+{
+    sla::DrainHole hole{Vec3f(0,0,0), Vec3f(0,0,1), 5, 10};
+    std::array<std::pair<float, Vec3d>, 2> out;
+    Vec3f s;
+    Vec3f dir;
+
+    // Start inside the hole and cast perpendicular to its axis.
+    s = {-1.f, 0, 5.f};
+    dir = {1.f, 0, 0};
+    hole.get_intersections(s, dir, out);
+    REQUIRE(out[0].first == Approx(-4.f));
+    REQUIRE(out[1].first == Approx(6.f));
+
+    // Start outside and cast parallel to axis.
+    s = {0, 0, -1.f};
+    dir = {0, 0, 1.f};
+    hole.get_intersections(s, dir, out);
+    REQUIRE(std::abs(out[0].first - 1.f) < 0.001f);
+    REQUIRE(std::abs(out[1].first - 11.f) < 0.001f);
+
+    // Start outside and cast so that entry is in base and exit on the cylinder
+    s = {0, -1.f, -1.f};
+    dir = {0, 1.f, 1.f};
+    dir.normalize();
+    hole.get_intersections(s, dir, out);
+    REQUIRE(std::abs(out[0].first - std::sqrt(2.f)) < 0.001f);
+    REQUIRE(std::abs(out[1].first - std::sqrt(72.f)) < 0.001f);
+}
+
+
 // Create a simple scene with a 20mm cube and a big hole in the front wall 
 // with 5mm radius. Then shoot rays from interesting positions and see where
 // they land.