@c -*-texinfo-*-
@node HOWTO Camera Movement, Space Warping, Cameras and Matrices, Engine
@subsection Camera Movement
@cindex movement, camera
@cindex moving, camera
@cindex @code{LookAt}
@cindex @code{csOrthoTransform}
@cindex @code{csReversibleTransform}
@cindex @code{iCamera}
@cindex world space
@cindex camera space

This section describes how to move the camera.

@subsubheading The Camera is a Transform

Internally in the engine the @samp{csCamera} class inherits
directly from @samp{csOrthoTransform} which inherits from
@samp{csReversibleTransform}. If you work with @samp{iCamera} then you
can get the reference to this transform with @code{camera->GetTransform()}.
In addition to the transformation a camera also holds a pointer to the
current sector.

This means that all operations you have in @samp{csOrthoTransform} can
be used on the camera. One of the most useful functions there is
@code{LookAt()} with which you can make the camera point to some spot.
Using @code{LookAt()} it is very easy to make a 3rd person view.

In addition to the standard functions from @samp{csOrthoTransform} there
are a number of other functions that you can use. The most interesting
are @code{MoveWorld()} and @code{Move()}. These functions will move
the camera and make sure that it cannot walk through a wall and also make
sure that walking through portals will work. Both functions move the
camera a relative amount. The difference between @code{MoveWorld()} and
@code{Move()} is that the latter will move the camera in camera space.
For example, take the following code:

@example
iCamera* camera;
camera->GetTransform ().Move (csVector3 (0, 0, 1));
@end example

This will move the camera forward in camera space. This means that the
camera will walk 'forward' :-) On the other hand:

@example
iCamera* camera;
camera->GetTransform ().MoveWorld (csVector3 (0, 0, 1));
@end example

This will move the camera in the world so that it goes one unit in
the positive Z direction. This will happen independently of the orientation
of the camera.

Here is another example which demonstrates how to use the @code{LookAt()}
function. The following example will set a camera at location @samp{3,5,1}
and let it look at @samp{3,5,10}. The up vector of the camera will be
@samp{0,1,0} (which is default):

@example
csVector3 camera_pos (3, 5, 1);
csVector3 look_at_pos (3, 5, 10);
csVector3 up (0, 1, 0);
camera->GetTransform ().Move (camera_pos);
camera->GetTransform ().LookAt (camera_pos - look_at_pos, up);
@end example

@subsubheading Include Files

The include files useful for this section are:

@example
#include <iengine/camera.h>
#include <csgeom/transfrm.h>
@end example
