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# Method to Calculate the Intensity for Polygonal Surfaces Under Transformation in Shading

IP.com Disclosure Number: IPCOM000119382D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 3 page(s) / 77K

IBM

## Related People

Liang, BCC: AUTHOR [+2]

## Abstract

A procedure to calculate the intensity values at the vertices of a polygonal surface under transformation (see Fig. 1) for shading in computer graphics is disclosed. The implementation of the GOURAUD shading algorithm in computer graphics requires the calculation of the unit normal vector at various points on a surface of a polygon. When the surface of the polygon is approximated by polygon patches, the usual approximation to the unit normal at a vertex is obtained by averaging the unit normals to the faces incident to the vertex.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method to Calculate the Intensity for Polygonal Surfaces Under Transformation

A procedure to calculate the intensity values at the
vertices of a polygonal surface under transformation (see Fig. 1) for
shading in computer graphics is disclosed.  The implementation of the
GOURAUD shading algorithm in computer graphics requires the
calculation of the unit normal vector at various points on a surface
of a polygon.  When the surface of the polygon is approximated by
polygon patches, the usual approximation to the unit normal at a
vertex is obtained by averaging the unit normals to the faces
incident to the vertex.

The procedure is used in a pipeline architecture (see Fig. 2)
and has the advantage of using fewer registers as well as eliminating
many calculation steps.

The prior art determines a unit normal vector for each surface
incident to the vertex, calculates the length of each such normal,
divides each normal by its length to obtain the unit normal which is
then used in the GOURAUD shading algorithm to determine the vertex
intensity.

The method for calculating pixel intensity values for a polygon
under transformation and to be displayed by a graphics display system
include the following steps:

The use of a front-end processor in a pipeline processing
system to calculate system constants, coordinates of the transformed
light source and the viewpoint, the transformation matrix and the
norm of the matrix inverse.

The use of a transformation processor in a pipeline processing
system to calculate pixel intensity values and transformed
coordinates of the vertices of the polygon under transformation
employing the outputs of the front-end processor.

The...