Quote:I want to ask a question?
the vUp is not the same as y-axis??

z-axis = Normalize(pAt - pEye)
x-axis = Normalize(pUp x z-axis) <- this is a cross product
y-axis = (z-axis x x-axis) <- this is a cross product

No, because the angle between pUp and z-axis can be different from 90 degrees.
That procedure always generate an ortho coordinate system to the camera. That is, the angles between the axes are always 90 degrees.

For example:

For these vectors:
D3DXVECTOR3 pEye( 0.0f, 10.0f, -10.0f );
D3DXVECTOR3 pAt( 0.0f, 0.0f, 0.0f );
D3DXVECTOR3 pUp( 0.0f, 3.0f, 0.0f );

D3D would create these axes:
z-axis = Normalize(pAt - pEye) = ( 0.0f , -0.707f , 0.707f )
x-axis = Normalize(pUp x z-axis) = ( 1.0f , 0.0f , 0.0f )
y-axis = (z-axis x x-axis) = ( 0.0f , 0.707f , 0.707f )

Note that pUp is different from the y-axis.

GDMichael, keep in mind that you DON'T generate the axes for the camera. Direct3D DOES that for you. You give three vectors (pEye, pAt and pUp) to it, by putting them in the D3DXMatrixLookAtLH/RH function. Then, Direct3D returns a view matrix to you. Just that.

Everything you need to move the camera is to specify its position (pEye), its target (pAt) and its orientation (pUp).

Again, the camera's axes are an intern operation made by Direct3D every time that you call the D3DXMatrixLookAtLH/RH function.

Well, now answering your questions:

Quote:1. When we move the camera staight along forward / bacwarad, we just move camera from the z-axis forward/backward, right?

Yes, but it is not good to think in that way. To move the camera on a straight path, you need to specify a directional vector for the path. The camera's z-axis is generated after that directional vector, and follows it.

Quote:2. When we move the camera up / down, we just move the camera along the y-axis, right?

If the movement is relative to the world space, the answer is: not necessarily. If both eye and target from the camera are not in a horizontal plane, the y-axis won't have a vertical direction.
But if the movement is relative to the camera's orientation, the answer is yes.

Quote:3. When we move the camera left or right (straft), we just move the camera along the x-axis, right?

The same thought of the previous answer.

Quote:4. When we use D3DXVec3Subtract two vector, does it have any orders, such as v1 -v2 = v2 - v1. D3DXVec3Subtract function, there has two vector parameter, which one is from and which one is to? Because I say your code below, the z-axis is subtract(vAt, vEye), but I don't sure which one is from or to, if vEye is from, that looks like correct, else, it seems not correct....

Well, v1-v2 = v2-v1 only if v1=v2=0. Sure the D3DXVec3Subtract function has an order:

D3DXVec3Subtract( &v3, &v2 &v1 ) -> v3 = v2 - v1 (doing a simple test you can know this)

Again, subtract(vAt, vEye) is an intern operation made by D3D to create z-axis. You DON'T do that.

Quote:5. Considering the up vector from the D3DXMatrixLookAtLH, is the up vector is considered from camera, therefore, it may not the same value of y-axis?

The up vector is an input for the D3DXMatrixLookAtLH function. It is NOT the y-axis from the camera. Please, read my last post again.

Quote:Please tell me the answer about the above questions, and also, I think I almost understand what you say, but I have a little question, when we normalize a vector such as vRight(x-axis), we will multiply the a constant speed to the vRight, after that, we will add vRight to the vEye and vLookAt. This method is just add a unit speed to the coordinate of the camera system, it is not really add an value to the axis, for example
if the unit vector of right is (2, 2, 0), and the speed is 3.0f, and the vEye is (1,2,3). after calucation, the new vEye is (7, 8, 3). (7, 8, 3) is just added by a unit speed, not a constant speed, why?

My english is not good, hope you can understand what I say..

Sorry... I understood nothing...


But I have some suggestions [smile]:

- At Google, search for tutorials about vectorial algebra, cross product, dot product etc. If you have some vectorial algebra book, better. Spend a time studying the math concepts behind that.
- Always consult the DX SDK. It has all the D3D's functions syntaxes and much more. There you can know which is the input/output of the D3D functions.

Good luck!

wait... wait...[totally] Be not nervous, OK?! [smile]
Maybe we are talking about different vectors, so the doubts will never be solved! [smile] Let us begin again:

Who are the vectors vEye, vLookAT and vUp that you mentioned in the last post? Are they the axes from the camera or the input of the D3DXMatrixLookAtLH function?

Please, answer that while I read your last post again [smile].

As our English is not good, perhaps we were communicating like two senile grandpas. [lol]