# Rotation Matrix from Vector in DirectX

This topic is 2439 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

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?

##### Share on other sites
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?

##### Share on other sites
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.

##### Share on other sites
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.

##### Share on other sites
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?

##### Share on other sites
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.

##### Share on other sites
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?

##### Share on other sites
Another source for a LookAt matrix (code here).

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

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

1. 1
Rutin
70
2. 2
3. 3
4. 4
5. 5

• 21
• 10
• 33
• 20
• 9
• ### Forum Statistics

• Total Topics
633422
• Total Posts
3011804
• ### Who's Online (See full list)

There are no registered users currently online

×