What if one triangle lie inside other triangle in the same plane. Or a line segment in a triangle?
How would the algorithm rasterize then?
@sjip Probably very badly! Recall the z-fighting artifact that I demoed in class a couple times. This happens when two triangles are nearly co-planar, since the depth buffer precision is not sufficient to correctly resolve occlusion. When two triangles are exactly co-planar (but have different vertex coordinates) you're sure to get garbage. :-)