Game Development Reference
In-Depth Information
in grabbing the world around you by manipulating it like an object. Any point of the
world is attached to the hand and used as a pivot point for manipulating the world that
follows the movements of the hand. This solution is very well suited to manipulation
set-ups like the Virtual Work Plan where the size of the scene is often relatively limited
(small number of objects). For sets-ups dedicated to applications of navigation in big
spaces (museums ... ), it may be desirable to deactivate the rotations so that the view
is not turned. Moreover, the “Grab the air'' technique permits standardisation of tools
between manipulation of objects and movement. The techniques of manipulation of
remote objects like ray tracing or the Go-go method can be used (see the part on
selection and manipulation of objects).
Manipulation of fixed objects
An alternative to the previous technique consists in selecting an object of the scene,
freezing it in the world and manipulating the world by manipulating this object. Like
the previous solution, this technique has the advantage of permitting standardisation
of tools for manipulation and movement.
12.4.2.3 Movement of the viewpoint
In some cases, it is preferable to control its movement by moving the camera (i.e. the
viewpoint) In this case, the control of movement cannot be done in the user view. This
view does not permit the camera to be seen. We then resort to a second view that is
often much larger. Generally, we are talking about either a map that is displayed on
a secondary view, like a handheld PDA, or a miniature representation of the virtual
world referred to as “World in miniature'', WIM. The map makes it possible to move
the viewpoint in a horizontal plane. The user view constantly reflects the position (and
the orientation) of the camera on the map.
WIM is a technique proposed by Stoakley et al. (1995), it can also be used in an
identical manner for discrete control (see below). A miniature of the virtual world (a
model) is provided to the user. He generally holds it in his non-dominant hand and
moves the camera with the help of his dominating hand.
The advantage of the two solutions presented (map and WIM) is the presence of
a second enlarged view. These two solutions allow the user place himself better and to
direct his movement better (see the section on wayfinding). The disadvantage, however,
is the presence of a second view that shifts the user's view from the main view, which
may result in him missing something important on the main view. The WIM solution
offers the advantage of letting the viewpoint move in space.
The WIM technique is also proposed for selection/manipulation of objects (see
section 12.5 for more details).
12.4.3 Discrete control
When control of continuous movement is often the preferred approach, using discrete
control for it is preferred in certain cases. Discrete control illustrates situations where
the user has a well-defined “target'' and attaches little importance to the manner in
which to achieve it. In this case, he names his target which can be an object of the
scene that is displayed on his view, which he selects (for example, with a virtual ray),
or an object displayed on a secondary view, like WIM, for example. You can also, in a
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