SOLIDWORKS model is utilizing 3D rendering engines (such as DirectX and OpenGL) to draw the geometry in the graphics area.
SOLIDWORKS API enables 3rd party add-ins and macros to inject 3D graphical objects directly into the model layer using OpenGL functions.
In this case geometry is embedded into the graphics view and transformed together with the model itself. It means that is is not required to calculate the transformation matrix.
Open GL graphics should be rendered within the [BufferSwapNotify] (http://help.solidworks.com/2018/english/api/sldworksapi/solidworks.interop.sldworks~solidworks.interop.sldworks.dmodelviewevents_bufferswapnotifyeventhandler.html) event of IModelView interface.
Explore this section for code examples and macros which demonstrate the usage of OpenGL to render objects in views using SOLIDWORKS API.