I made a camera in DX9. To move forward I press the Up arrow. To rotate on the Y axis I use the mouse. When I perform these movements on their own the camera moves at the speed I want.

However, if I hold down Up and move the mouse at the same time then the camera moves a lot faster than it should. I want it to move at the same speed as it does when only the Up arrow is pressed.

I think I need to normalize something somewhere but not sure what and not sure where. Have tried various combinations without success so if anyone can point me in the right direction that would be great.

Thanks.

My code

#define KEY_DOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)

LRESULT WINAPI MsgProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
    if( KEY_DOWN(VK_UP))    MovePlayer(D3DXVECTOR3(0, 0, -1.0f));
    if( KEY_DOWN(VK_DOWN))  MovePlayer(D3DXVECTOR3(0, 0, 1.0f));

    switch( msg )
    {
        case WM_MOUSEMOVE:
        ProcessMouseInput();
    }
}

void  MovePlayer( D3DXVECTOR3 in_vec )
{
    D3DXMATRIX CameraRot; 
    D3DXMatrixRotationY(&CameraRot,D3DXToRadian(AngleY));
    D3DXVECTOR3 CameraRotTarget;
    D3DXVec3TransformNormal(&CameraRotTarget,&in_vec,&CameraRot);
    CameraPos +=  (m_timeElapsed * CameraRotTarget);
}


void ProcessMouseInput()
{
    GetCursorPos( &CurrentMouseState );

    if ((CurrentMouseState.x != GameMouseState.x) || (CurrentMouseState.y != GameMouseState.y))        
    {
        int dx = CurrentMouseState.x - GameMouseState.x;                
        int dy = CurrentMouseState.y - GameMouseState.y;   
        AngleY+=m_timeElapsed*dx*7.0f;        
    }
    GameMouseState = CurrentMouseState;
    // Set back to window center in Render function
}

VOID UpdateCamera()
{ 
    D3DXVECTOR3 CameraOrigTarget(0, 0, -1); 
    D3DXVECTOR3 CameraOrigUp(0, 1, 0);

    D3DXMATRIX CameraRot; 
    D3DXMATRIX CameraRotX; 
    D3DXMatrixRotationX(&CameraRotX,D3DXToRadian(AngleX));
    D3DXMATRIX CameraRotY; 
    D3DXMatrixRotationY(&CameraRotY,D3DXToRadian(AngleY)); 
    CameraRot = CameraRotX * CameraRotY;
    D3DXVECTOR3 CameraRotTarget;
    D3DXVec3TransformNormal(&CameraRotTarget,&CameraOrigTarget,&CameraRot);

    D3DXVECTOR3 CameraTarget;
    CameraTarget = CameraPos + CameraRotTarget;  

    D3DXVECTOR3 vUpVec( 0.0f, 1.0f, 0.0f );
    D3DXMatrixLookAtLH( &matView, &CameraPos, &CameraTarget, &vUpVec );
    g_pd3dDevice->SetTransform( D3DTS_VIEW, &matView );

    D3DXMatrixPerspectiveFovLH( &matProj, D3DX_PI / 4, 1.0f, 1.0f, 100.0f );
    g_pd3dDevice->SetTransform( D3DTS_PROJECTION, &matProj );
}