I'm trying to simulate a centipede game, and I'm doing the snake movement. I have seen that piece of code, but can't get it, I know it gets the different between the current, previou's nodes positions, but what is the point of multiplying by the normal vector ?
for ( int i = 1 ; i < nodes.size(); i++ )
{
Vec2f diff = nodes[i-1].m_Pos-nodes[i].m_Pos;
float length = diff.length();
Vec2f norm = diff.normalized();
nodes[i].m_Pos+=(length - 5)*norm;
}
In mathematics, a vector is said to be normal to a surface if it is perpendicular. In other words, normal vectors always point directly away from something.
Multiplying a scalar by a normal vector will get you a vector that represents displacement in the direction of the normal. Often normals have a handy property that they are unit-length, so if you want to move 5 units in the normal direction, nothing more than a multiplication is necessary. If it is not the case that the normal is unit-length, then an expensive normalization will be required.
Now, I am concerned by the naming in this code snippet. Norm actually has a different meaning from normal. In many contexts, the norm is actually the length, size or extent. A vector's norm, for instance, is a scalar that represents its length.
The fact that directly above the variable named norm is another variable named length and norm is declared as a vector rather than a scalar give enough context clues to indicate that norm is probably short-hand for normal, but this is poor naming.
