How is support generated when printing?

[nguyentruc1196 0]

Hello everyone, 
I'm doing a research project for a course in university, one component of which requires me to figure out how support structures are generate for each print job. Let me clarify:
Given a random 3D model, how does Cura calculate the amount and where support is needed? Does Curado it differently compared to other slicers or is it somewhat similar across all of them? 
From using Cura it seems to me that Cura looks at each triangular surface's normal, which is stored in the STL file, but this is just my assumption, so I wonder if anyone knows how they do it. 
Any help is greatly appreciated. Thank you. 
 

[ahoeben 1,968]

CuraEngine does not use the surface normals. These can often be incorrect (or missing altogether). Instead CuraEngine first slices the model into layers (from the bottom up), and then does a pass over each layer from top to bottom to see if the layer underneath it properly supports it. If not, additional support structures are added.