Game Development Reference
In-Depth Information
The value of the second nonparallel vector is as follows:
Vector 2
=
V2
-
V3
V1
,
V2
, and
V3
are the three vertices of a triangle primitive.
The calculation of the normal at a vertex shared by multiple triangles/primitives
is a little complicated as both primitives contribute to its calculation. The following
diagram shows a vertex,
V4
, shared between triangles
1
and
2
:
N
N
1
N
2
V
4
1
2
V
1
V
3
V
2
N = N
1
+
N
2
... N
n
Hence, if two primitives, (
V1
,
V2
,
V4
) and (
V2
,
V4
,
V3
), share a common vertex,
V4
, then we will calculate
N1
from the primitive
1
(
V1
,
V2
,
V3
) and
N2
from the
primitive
2
(
V2
,
V3
,
V4
), and the final normal
N
on vertex
V4
would be the vector
sum of
N1
and
N2
.
Calculating normals from vertices and indices
Open the
02-NormalCalculation.html
file in your favorite text editor. A normal is
the cross-product of the vectors with common vertices as discussed in the preceding
section. The following code calculates the
normals
array from the
vertices
and
indices
arrays:
function calculateVertexNormals(vertices,indices){
var vertexVectors=[];
var normalVectors=[];
var normals=[];
for(var i=0;i<vertices.length;i=i+3){
var vector=
vec3.fromValues(vertices[i],vertices[i+1],vertices[i+2]);
var normal=vec3.create();//Initialized normal array
normalVectors.push(normal);
vertexVectors.push(vector);
}
