Fix for normal averaging and hidden parameter for max normal Z angle.

src/libslic3r/SLA/SLASupportTree.cpp

@@ -1085,7 +1085,8 @@ bool SLASupportTree::generate(const PointSet &points,
             double polar = std::acos(z / r);
             double azimuth = std::atan2(n(1), n(0));
 
-            if(polar >= PI / 2) { // skip if the tilt is not sane
+            // skip if the tilt is not sane
+            if(polar >= PI - cfg.normal_cutoff_angle) {
 
                 // We saturate the polar angle to 3pi/4
                 polar = std::max(polar, 3*PI / 4);

src/libslic3r/SLA/SLASupportTree.hpp

@@ -67,6 +67,10 @@ struct SupportConfig {
     // The elevation in Z direction upwards. This is the space between the pad
     // and the model object's bounding box bottom.
     double object_elevation_mm = 10;
+
+    // The max Z angle for a normal at which it will get completely ignored.
+    double normal_cutoff_angle = 110.0 * M_PI / 180.0;
+
 };
 
 struct PoolConfig;

src/libslic3r/SLA/SLASupportTreeIGL.cpp

@@ -188,7 +188,15 @@ PointSet normals(const PointSet& points, const EigenMesh3D& emesh,
             neighnorms.emplace_back(U.cross(V).normalized());
         }
 
-        // Throw out duplicates. They would case trouble with summing.
+        // Throw out duplicates. They would cause trouble with summing. We will
+        // use std::unique which works on sorted ranges. We will sort by the
+        // coefficient-wise sum of the normals. It should force the same
+        // elements to be consecutive.
+        std::sort(neighnorms.begin(), neighnorms.end(),
+                  [](const Vec3d& v1, const Vec3d& v2){
+            return v1.sum() < v2.sum();
+        });
+
         auto lend = std::unique(neighnorms.begin(), neighnorms.end(),
                                 [](const Vec3d& n1, const Vec3d& n2) {
             // Compare normals for equivalence. This is controvers stuff.