Contents
How to get the normal at a vertex?
One way is to average the normals of all triangles that share a vertex in order to obtain the normal at that vertex. This obviously requires connectivity information (or you need to extract it somehow). Once you have three different normals (say na, nb, nc), then the normal at any interior point can be computed via barycentric coordinates.
Which is vertex does not have four incident faces?
The most widely referred to is an extra-ordinary vertex, i.e. a vertex which, in the case of a quad subdivision scheme like Catmull-Clark, does not have four incident faces. The presence of these irregular features makes the limit surface around them similarly irregular, i.e. it cannot be represented as simply as it can for regular regions.
Which is an irregular feature of a subdivision?
Irregular features come in a number of forms. The most widely referred to is an extra-ordinary vertex, i.e. a vertex which, in the case of a quad subdivision scheme like Catmull-Clark, does not have four incident faces.
Do you have to interpolate surface normal across interior of triangle?
The assumption in that case, is that the entire triangle is flat. This is called flat shading. If, on the other hand, you wish to interpolate the surface normal across the interior of a triangle (used in Gouraud shading ), then you need to have three different normals at the three vertices to begin with.
How are barycentric coordinates computed in rasterization?
While in screen space, the triangle is “rasterized”. If a pixel overlaps the triangle, the barycentric coordinates of that pixel are computed.
When do vertex normals have to be computed on the fly?
Sometimes triangles mesh are not directly converted from a smooth surface, and vertex normals have to be computed on the fly. Different techniques for computing vertex normals when there is not smooth surface to compute them from exist, but we won’t study them in this lesson.
How to calculate the point interpolated smooth normal?
All you need to do then, is to combine the point barycentric coordinate and the triangle vertex normals to compute the point interpolated smooth normal (lines 17-20 below): Note that this only produces the impression that the surface is smooth.