// 计算观察矩阵
public Matrix4x4 LookAt()
{
Matrix4x4 view = new Matrix4x4();
Vector4 xaxis, yaxis, zaxis;
zaxis = Target - Position;
zaxis.Normalize();
xaxis = Vector4.Cross(Up, zaxis);
xaxis.Normalize();
yaxis = Vector4.Cross(zaxis, xaxis);
yaxis.Normalize();
view.M[0, 0] = xaxis.X;
view.M[1, 0] = xaxis.Y;
view.M[2, 0] = xaxis.Z;
view.M[3, 0] = -Vector4.Dot(xaxis, Position);
view.M[0, 1] = yaxis.X;
view.M[1, 1] = yaxis.Y;
view.M[2, 1] = yaxis.Z;
view.M[3, 1] = -Vector4.Dot(yaxis, Position);
view.M[0, 2] = zaxis.X;
view.M[1, 2] = zaxis.Y;
view.M[2, 2] = zaxis.Z;
view.M[3, 2] = -Vector4.Dot(zaxis, Position);
view.M[0, 3] = view.M[1, 3] = view.M[2, 3] = 0.0f;
view.M[3, 3] = 1.0f;
return(view);
}
//消隐
private bool ShouldBackFaceCull(VertexTriangle oriVt)
{
Vector4 a = new Vector4(oriVt.Vertices[0].ScreenSpacePosition);
Vector4 b = new Vector4(oriVt.Vertices[1].ScreenSpacePosition);
Vector4 c = new Vector4(oriVt.Vertices[2].ScreenSpacePosition);
a.Z = b.Z = c.Z = 0;
Vector4 ab = b - a;
Vector4 ac = c - a;
return(Vector4.Cross(ab, ac).Z > 0);
}
