Programming with DirectX : View Transformations

The view transformation matrix is a matrix that represents the viewer. The viewer is commonly known as the game’s camera. A camera is represented by a position and a direction in which it is pointing. In OpenGL and Direct3D, camera matrices are often known as look-at matrices. In Direct3D a look-at matrix can be created using either a left- or right-handed function much like the projection matrix. These functions are called D3DXMatrixLookAtLH() and D3DXMatrixLookAtRH() and have the following prototypes.

D3DXMATRIX * D3DXMatrixLookAtLH(
   D3DXMATRIX *pOut,
   CONST D3DXVECTOR3 *pEye,
   CONST D3DXVECTOR3 *pAt,
   CONST D3DXVECTOR3 *pUp
);

D3DXMATRIX * D3DXMatrixLookAtRH(
   D3DXMATRIX *pOut,
   CONST D3DXVECTOR3 *pEye,
   CONST D3DXVECTOR3 *pAt,
   CONST D3DXVECTOR3 *pUp
);

The eye vector is the 3D position of the camera. The look-at vector is the position in 3D space at which you are looking. The position you are located at and the position you are looking at define the view’s direction. The up vector is a vector that represents which direction is up. The up vector can be used to allow the camera to be rotated. In a first-person camera, this can be used to rotate the position you are looking at (look-at point) around the up vector to look around you from left to right.

We’ll hold off on discussing the details about views, as well as matrices in general. The purpose of this demo is to see how to transform vectors in a vertex shader; the details and math behind it beyond what was discussed in this chapter come later.

The concatenation of the projection, world, and view matrices forms the model-view projection matrix. This is also known as the MVP matrix.