catch bad acos args that cause nans

src/shapes.cpp

@@ -404,7 +404,6 @@ void Mesh::scaleAndPadd(double scaleX, double scaleY, double scaleZ, double padd
     double scaledX = sx + dx * scaleX;
     double scaledY = sy + dy * scaleY;
     double scaledZ = sz + dz * scaleZ;
-
     // Padding in each direction
     vertices[i3] = scaledX + vertex_normals[i3] * paddX;
     vertices[i3 + 1] = scaledY + vertex_normals[i3 + 1] * paddY;
@@ -548,7 +547,14 @@ void Mesh::computeVertexNormals()
       if (vec1_norm == 0.0 || vec2_norm == 0.0)
         return 0.0;
 
-      return std::acos(vec1.dot(vec2) / (vec1_norm * vec2_norm));
+      auto acos_arg = vec1.dot(vec2) / vec1_norm * vec2_norm;
+      // std::acos range is [-1.0, 1.0] and returns nans if arg > 1.0
+      // if the arg is approximately 1.0 return 0.0 angle as float imprecision will lead to nans
+      if (std::abs(acos_arg - 1.0) < 1e-6)
+      {
+        return 0.0;
+      }
+      return std::acos(acos_arg);
     };
 
     // Use law of cosines to compute angles