9 replies to this topic

[lukesmith123]

Hi,

I have a direction vector and I want to create a rotation matrix from it. This is what I am trying:

//direction = 0, 0, 1
//up		   = 0, 1, 0
//right		= 0, 0, 0

D3DXVec3Normalize(&direction, &direction);
//right
D3DXVec3Cross(&right, &up, &direction);
D3DXVec3Normalize(&right, &right);

rot(0,0) = right.x;
rot(1,0) = right.y;
rot(2,0) = right.z;
rot(3,0) = 0;  
rot(0,1) = up.x;
rot(1,1) = up.y;
rot(2,1) = up.z;
rot(3,1) = 0;
rot(0,2) = direction.x;
rot(1,2) = direction.y;
rot(2,2) = direction.z;
rot(3,2) = 0;  
rot(0,3) = 0.0f;
rot(1,3) = 0.0f;
rot(2,3) = 0.0f;
rot(3,3) = 1.0f;

I had thought that his would work however it gives me an error where the model that uses the matrix is stretched and appears as a giant line across the screen.

Am I doing something wrong?

[Álvaro]

Your matrix always maps (0,1,0) to (0,1,0), but that's probably not what you want. What rotation exactly does the vector represent?

[lukesmith123]

I'm a little confused but the vector is the objects heading. So if the vector was 0,0,1 it would face on the positive z and if it were 0,0,-1 it would face -z.

[Álvaro]

A direction in three dimensions is not enough to describe a rotation. Think of a pencil pointing somewhere: You can still rotate it around the axis and it still points to the same place.

Perhaps you are trying to build a lookAt matrix. That looks a lot like your code.

[lukesmith123]

Ah that would explain why I'm getting so confused. So what would be the next step after determining the objects heading vector to create the rotation matrix?

[Álvaro]

Imagine I asked you that x is if I know that x+y=7. Obviously, you'd tell me that you can't tell me what x is, because there are many solutions. Well, your situation is very similar: Your problem is not completely specified.

[lukesmith123]

My problem is that I have the direction vector that the object should be facing and I want to create the world matrix with the object rotated in the direction defined by the vector.

I had thought that I could do this simply by finding the right vector from the direction vector and the up vector and filling the rows of the matrix with this information. But that appears to be incorrect so now I am wondering how this can be achieved?

[clb]

Another source for a LookAt matrix (code here).

[lukesmith123]

Ok so is it possible to orient an object with a lookat matrix? otherwise how do I go from direction vector to world matrix?

[lukesmith123]

EDIT: Ah I realised I had made a stupid mistake elsewhere and the code that I originally posted was fine. Sorry!