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