directx c++ first person camera - c++

Question

im creating a 3d room which you can walk around with a first person camera
i have defined the position of the eyeX eyeY and eyeZ as shown below:
float eyeX = 0;
float eyeY = 100;
float eyeZ = 75;
here is my lookat code:
D3DXMatrixLookAtLH( &g_matView, &D3DXVECTOR3( eyeX, eyeY,eyeZ ),
&D3DXVECTOR3( LookatX, LookatY, LookatZ ),
&D3DXVECTOR3( 0.0f, 1.0f, 0.0f ) );
g_pd3dDevice->SetTransform( D3DTS_VIEW, &g_matView );
my code allows me to move the camera around but not like a first person camera and i am struggling to achieve this.
// forwards = UP ARROW
// Backwards = DOWN ARROW
// rotate left = LEFT ARROW
// rotate right = RIGHT ARROW
case WM_KEYDOWN:
{
// Handle any non-accelerated key commands
switch (wparam)
{
case VK_RIGHT:
if(eyeX >=-50)
{
--eyeX;
}
return (0);
case VK_LEFT:
if(eyeX <=50)
{
++eyeX;
}
return (0);
case VK_DOWN:
if(eyeZ >=-50)
{
--eyeZ;
}
return (0);
case VK_UP:
if(eyeZ <=50)
{
++eyeZ;
}
return (0);
case VK_SPACE:
if(eyeY >=-50)
{
--eyeY;
}
return (0);
case VK_SHIFT:
if(eyeY <=50)
{
++eyeY;
}
return (0);
}
break;
}
LookatX = eyeX + 5.0f;
LookatY = eyeY;
LookatZ = eyeZ;
case WM_DESTROY:
{
// kill the application
PostQuitMessage(0);
return(0);
}
default:
break;
} // end switch
could anyone suggest some changes which would allow me to move around my room like a first person camera?

Answer 1

Instead of using D3DXMatrixLookAtLH, you could keep a view matrix.
Set up
(Note that I am making up names of functions, you might have to create these yourself)
Start with something like
Matrix view = Matrices.createIdentity();
Then every frame, you set the view matrix(just like you are doing with the matrix you are getting from MatrixLookAtLH)
Moving around
Normally modifing a model matrix is like this.
model = Matrix.multiply(model,transformation).
However, you manipulate the camera backwards
view = Matrix.multiply(transformation, view)
Simply run your switch statement, generate a transformation and update the view matrix.
e.g:
if (key == 'w')
view = Matrix.multiply(Matrices.createTranslate(0,0,-5), view);
if (key = 'j') // Key to turn
view = Matrix.multiply(Matrices.createRotateY(.1), view);
Formulas for genereating these matrices can be found on wikipedia(or DirectX might give them on its own).
(This is all based off of a simple software renderer I made a while ago, but it should apply the same to DirectX)
EDIT:
Oh, it looks like DirectX has all of these functions for you already in http://msdn.microsoft.com/en-us/library/windows/desktop/bb281696(v=vs.85).aspx