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# 4x4 rotation matrix

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Hello everyone, In DirectX 8.0, assuming i already got 3 normalized D3DXVECTOR3 vectors: a forward vector, an up vector, and a right vector, how can i use these to build up a rotation matrix that can be multiplied by the world matrix with the translation matrix for displaying an object. I already got the direction vectors (as stated above), i just need to know how to put them into the 4x4 matrix (where they go in the D3DXMATRIX) and use that as the rotation matrix or can you not use that data directly for the rotation matrix and some how have to build one up? Sincerely, Scott Richmond Viper Digital

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Your question is not very clear, that is why the reply below may or may not be what you looking for.

you store your object translation, and rotation in matrecies which you look to know that.Then you combine all those matrecies together to produce the final behavior of the object, nothing about the object orientation on 3d and on the screen yet.

The view and projection matrecies are set indpendent of each other and indpendent of the object transformation matrix.

Then as you indicated you multiply the three matrices to transfer the vertecies from there own axis into the screen axis.

There are plenty of tutorials that clearly explains this subject, you may wana look to the sdk/samples/multimedia/direct3d/tutorials/tutorial3

If love is illusion and hate is real, I would rather be crazy

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Scott,

Here's one way that will work, though probably not the most efficient (I'm curious to see the methods posted by others).

A thread a few days ago had to do with how to rotate a "monster" character to face the camera. I am getting some of this algorithm from the code suggested by nyStagmus in that thread.

Here's some C++ (untested, mind you):

    // D3DXVECTOR3 translation;   // translation offsets// D3DXVECTOR3 lookAt, up; // look-at, up vectorsD3DXMatrix inverseMatrix, worldMatrix;D3DXMatrixLookAtLH(&inverseMatrix, &translation, &lookAt, &up);D3DXMatrixInverse(&worldMatrix, NULL, &inverseMatrix);// NOTE: the following block of code may not be necessary...worldMatrix._41 = translation.x;worldMatrix._42 = translation.y;worldMatrix._43 = translation.z;

Note that I do not know if the last block of code is necessary or not; I don't know if D3DXMatrixLookAtLH actually creates a translation offset from parameter 2 or if it just uses parameter 2 to compute rotation angles. Try it yourself and see!

(edit: replaced "right" vector with "up" vector in code.)
--Hoozit.

[edited by - HoozitWhatzit on July 23, 2002 1:55:03 AM]

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If you already have the 3 vectors, and they''re all normalised and at right angles to each other (and they weren''t expensive to calculate, a few crossprods is still usually cheaper than an inverse):

1. Set the matrix to identity (to clear out the elements you aren''t using).

2. Set the following members of the matrix:
_11 = right.x;
_21 = right.y;
_31 = right.z;
_12 = up.x;
_22 = up.y;
_32 = up.z;
_13 = forward.x;
_23 = forward.y;
_33 = forward.z;

The top 3x3 part of a 4x4 matrix is the bit which does rotations.
The 3, normalised, perpendicular vectors are known as an orthonormal basis (if you want to search for it to get yourself up to speed on the maths).

--
Simon O''Connor
Creative Asylum Ltd
www.creative-asylum.com

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