我有以下用于计算Heightmap法线的代码
void CalcMapNormals(HeightMap * map, Vec3f normals[])
{
int dst, i, j, right, bottom;
Vec3f p0, p1, p2;
Vec3f n0;
/* Avoid writing map->rows|cols - 1 all the time */
right = map->cols - 1;
bottom = map->rows - 1;
dst = 0;
for (i = 0; i < map->rows; i++) {
for (j = 0; j < map->cols; j++) {
Vec3Set(normals[dst], 0, 0, 0);
/* Vertex can have 2, 3, or 4 neighbours horizontally and vertically */
if (i < bottom && j < right) {
/* Right and below */
GetHeightPoint(map, i, j, p0);
GetHeightPoint(map, i + 1, j, p1);
GetHeightPoint(map, i + 1, j + 1, p2);
CalcTriNormal(n0, p0, p1, p2);
VecAdd(normals[dst], normals[dst], n0);
}
/* TODO: the other three possibilities */
VecNormalize(normals[dst]);
dst += 1;
}
}
/* Sanity check */
if (dst != map->rows * map->cols)
Fail("Internal error in CalcMapNormals: normals count mismatch");
}
我理解代码获取三角形的三个顶点,计算其法线然后添加它们并将它们标准化以获得平均法线。但我不知道你怎么能得到其他三种可能性,我一直在做类似以下的事情:
void CalcMapNormals(HeightMap * map, Vec3f normals[])
{
int dst, i, j, right, bottom;
Vec3f p0, p1, p2;
Vec3f n0;
Vec3f p3, p4, p5;
Vec3f n1;
Vec3f p6, p7, p8;
Vec3f n2;
Vec3f p9, p10, p11;
Vec3f n3;
/* Avoid writing map->rows|cols - 1 all the time */
right = map->cols - 1;
bottom = map->rows - 1;
dst = 0;
for (i = 0; i < map->rows; i++) {
for (j = 0; j < map->cols; j++) {
Vec3Set(normals[dst], 0, 0, 0);
/* Vertex can have 2, 3, or 4 neighbours horizontally and vertically */
if (i < bottom && j < right) {
/* Right and below */
GetHeightPoint(map, i, j, p0);
GetHeightPoint(map, i + 1, j, p1);
GetHeightPoint(map, i + 1, j + 1, p2);
CalcTriNormal(n0, p0, p1, p2);
VecAdd(normals[dst], normals[dst], n0);
}
if ( i > bottom && j > 0)
{
GetHeightPoint(map, i, j, p3);
GetHeightPoint(map, i + 1, j, p4);
GetHeightPoint(map, i, j -1, p5);
CalcTriNormal(n1, p3, p4, p5);
VecAdd(normals[dst], normals[dst], n1);
}
if ( i > 0 && j > 0)
{
GetHeightPoint(map, i, j, p6);
GetHeightPoint(map, i, j - 1, p7);
GetHeightPoint(map, i - 1, j, p8);
CalcTriNormal(n2, p6, p7, p8);
VecAdd(normals[dst], normals[dst], n2);
}
if ( i > bottom && j < right)
{
GetHeightPoint(map, i, j, p9);
GetHeightPoint(map, i-1, j, p10);
GetHeightPoint(map, i, j+1, p11);
CalcTriNormal(n3, p9, p10, p11);
VecAdd(normals[dst], normals[dst], n3);
}
/* TODO: the other three possibilities */
VecNormalize(normals[dst]);
dst += 1;
}
}
/* Sanity check */
if (dst != map->rows * map->cols)
Fail("Internal error in CalcMapNormals: normals count mismatch");
}
但我不认为它给了我想要的结果,我得到了正常平均的概念,但无法弄清楚代码。
答案 0 :(得分:1)
嗨Yzwboy这里是我尝试制作“平滑”法线的一种方法(基于相邻三角形的平均值):
为了计算“平滑”法线,你需要为每个顶点指定一个法线,该法线在与顶点相邻的三角形的法线上取平均值。
我会根据与所讨论的顶点相邻的两条边之间的角度来计算加权平均值(交叉积很容易计算):
<强>伪代码:强>
Vec3F faceNormal(int face_id, int vertex_id) // assumes C-->B-->A is clockwise
{
Vec3f A = triangleMesh.face[face_id].vertex[vertex_id]; // A
Vec3f B = triangleMesh.face[face_id].vertex[(vertex_id+1)%3]; // B
Vec3f C = triangleMesh.face[face_id].vertex[(vertex_id+2)%3]; // C
Vec3f BA = B-A;
Vec3f CA = C-A;
Vec3f Normal = BA.cross(CA);
float sin_alpha = length(Normal) / (BA.len() * CA.len() ); // depending on your implementation of Vec3f it could be .magnitude() or .length() instead of .len()
return (Normal.normalize() * asin(sin_alpha);)
}
然后通过顶点改变法线:
void computeNormals() {
for (vertex v in triangleMesh)
{
Vec3f Normal (0,0,0);
for (int i = 0;i < TriangleCount;i++)
if (triangleMesh.face[i].contains(v) )
{
int vertID = vertexPositionInTriangle(i,v); //Can be 0,1 or 2. Use an enum to make A = 0, B=1, C=2 if that is easier to read:)
Normal = Normal + faceNormal(i,vertID);
}
addNormalToVertexV(Normal.normalize(),v); // this is a function to set the normal for a vertex, the vertex class must have a member for normal though and the arguments for the function are Vec3f, Vec3f
}
}
您还可以计算每个三角形的面积以用作加权,但我发现使用这些角度最适合用于外观。
我曾尝试使用与Vec3f规范相匹配的名称,以及内置函数来节省工作,但是您需要进行一些编码才能使伪代码工作(我在这里无法访问GL测试环境)。
希望这会有所帮助:)