public static vec3[] GenerateNormalsForQuadMesh(vec3[] positions, uint[] indexes)
{
var faceNormals = new vec3[indexes.Length / 4];
for (int i = 0; i < indexes.Length / 4; i++)
{
uint vertexId0 = indexes[i * 4 + 0];
uint vertexId1 = indexes[i * 4 + 1];
uint vertexId2 = indexes[i * 4 + 2];
uint vertexId3 = indexes[i * 4 + 3];
vec3 vertex0 = positions[vertexId0];
vec3 vertex1 = positions[vertexId1];
vec3 vertex2 = positions[vertexId2];
vec3 vertex3 = positions[vertexId3];
vec3 normalA, normalB, normalC, normalD;
{
vec3 v1 = vertex0 - vertex2;
vec3 v2 = vertex2 - vertex1;
normalA = v2.cross(v1).normalize();
}
{
vec3 v1 = vertex0 - vertex3;
vec3 v2 = vertex3 - vertex2;
normalB = v2.cross(v1).normalize();
}
{
vec3 v1 = vertex0 - vertex3;
vec3 v2 = vertex3 - vertex1;
normalC = v2.cross(v1).normalize();
}
{
vec3 v1 = vertex1 - vertex3;
vec3 v2 = vertex3 - vertex2;
normalD = v2.cross(v1).normalize();
}
faceNormals[i] = (normalA + normalB + normalC + normalD).normalize();
}
var normals = new vec3[positions.Length];
for (int i = 0; i < positions.Length; i++)
{
vec3 sum = new vec3();
int shared = 0;
for (int j = 0; j < indexes.Length / 4; j++)
{
uint vertexId0 = indexes[i * 4 + 0];
uint vertexId1 = indexes[i * 4 + 1];
uint vertexId2 = indexes[i * 4 + 2];
uint vertexId3 = indexes[i * 4 + 3];
if (vertexId0 == i || vertexId1 == i || vertexId2 == i || vertexId3 == i)
{
sum = sum + faceNormals[j];
shared++;
}
}
if (shared > 0)
{
sum = (sum / shared).normalize();
}
normals[i] = sum;
}
return normals;
}
