#### 10.2.9 Fvisible

• Fvisible( <facet> )
• Description: that function returns $1$ or $0$ according to the fact that the <facet> is visible or not. A facet is visible if its normal vector is directed toward the observer (ie: the scalar product with the vector facet-observer, is positive). That function takes in count the current 3D transformation matrix and the projection type.