How does rendering of STEP parts in OOCT work

I am currently playing around with OCCT and doing some rendering in openGL by meshing the parts and then rendering the triangles.
However I've downloaded some sample STEP files, where meshing in FreeCad fails, however the file gets rendered correctyl in the GUI.
So I was wondering how it is done internally when meshing fails and it is also a lot faster then when I perform the meshing.

Kirill Gavrilov's picture

Meshing algorithm usually fails on specific TopoDS_Face sub-shapes with incorrect geometry definition or some problems.
It rarely fails on entire shape - therefore, failure of the algorithm doesn't mean that shape has no triangulation at all.

Displaying shaded model without triangulation is not possible - so calling BRepMesh is a normal process after model import.
What could be displayed instead is a Wireframe presentation - surface isolines and boundaries.