It is not so clear. Based on your equations, it seems you would like to rotate the view point around an axis that passes by the point (50,50,50) and has the x direction, correct?

Well, the pUp and (plookAt - pEye) vectors are used to generate a coordinate system for the camera. The x-axis's orientation of this coordinate system depends the angle between pUp and (plookAt - pEye), because a cross product always considers the smaller angle between two vectors to generate the 3th vector. In other words, on a cross product C = AxB, when you apply the left-handed rule (from A to B) to determine the direction/orientation of C (by the thumb), you always go on the smaller angle between A and B.

So, the problem in keeping the pUp vector constant (like you shown) is: If you change the (plookAt - pEye) direction, the camera coordinate system will be inverted when the angle between pUp and (plookAt - pEye) > 180 degrees.

To avoid this, you must update the pUp vector when the (plookAt - pEye) direction is changed. If you know (stored) the camera's x-axis, you could do:

D3DXVec3Cross( &pUp, &(plookAt - pEye), &Xaxis );

Then use pUp, plookAt and pEye to create the view matrix.

Quote:I want to rotate around the origin, on both the x and y axis's at a distance of 10;

Mathematically, we usually define a rotation around an axis (not around a point). This can confuse us. We are going for steps, OK?! [smile]. Firstly, let me understand exactly what you would like to do. I suppose you want the camera's eye position rotate spherically around the origin. So, your camera's target would be at the origin. Is it correct? If it is not correct, where is the camera's target?

Here is some simple code for your task

[edit: snip]

you need to modify your up vector as your lookat vector approaches the world up vector. You can cross the current lookat vector with the current right vector to get this.

Quote:Yes that is exactly it. But for now all I need to do is rotate the viewPoint around the x axis.

OK, now is easier [smile]:

// Inputs
if ( Left == TRUE )
x -= 0.01f;

if ( Right == TRUE )
x += 0.01f;

if ( Up == TRUE )
y += 0.01f;

if ( Down == TRUE )
y -= 0.01f;

// Using your notations
D3DXVECTOR3 point( 0.0f, 0.0f,10.0f );
D3DXVECTOR3 at( 0.0f, 0.0f, 0.0f );
D3DXVECTOR3 up( 0.0f, 1.0f, 0.0f );

D3DXMATRIX RotX, RotY, RotFinal;
D3DXMatrixRotationX( &RotX, y );
D3DXMatrixRotationY( &RotY, x );

RotFinal = RotX * RotY;

D3DXVec3TransformCoord( &point, &point, &RotFinal );

// Now the key: We also transform the up vector to avoid the "screen flip"
D3DXVec3TransformCoord( &up, &up, &RotFinal );

// Creating the view matrix
D3DXMATRIX matView;
D3DXMatrixLookAtLH( &matView, &point, &at, &up );
pDevice->SetTransform( D3DTS_VIEW, &matView );

// Creating the projection matrix
D3DXMATRIX matProj;
D3DXMatrixPerspectiveFovLH( &matProj, ... , ..., ... , ... );
pDevice->SetTransform( D3DTS_PROJECTION, &matProj );


Notice that this solution rotates the camera's eye around the X and Y axes from the world coordinate system. To rotate it around the camera's axes, you need to create a local coordinate system for the camera and using D3DXMatrixRotationAxis function [wink].