Game Development Reference
In-Depth Information
F collision
of objects
X, F
X, F
Figure 16.1 Software architecture for haptic rendering
Tactile feedback recreating the haptic sensation felt on touching a surface (for
example, roughness). This sensation is felt by the user owing to the sensors in
the skin;
Thermal feedback i.e. the recreation of thermal exchanges that take place at the
time of contact between two materials (not covered in this chapter).
The calculation of such forces of interaction derives a lot from physical model-based
animation techniques. In fact, to animate virtual objects, the physical animation
engines calculate the acceleration of each virtual object, as per the external forces
and constraints which it faces, and integrates it twice to obtain the final position.
If there is contact, the forces of reaction are calculated on the basis of collision
parameters (non penetration constraints, restitution coefficient for impact, friction
coefficient, etc.) and the physical parameters intrinsic to the objects (mass, inertia,
dynamic equation, etc.). These reaction forces are added to the dynamics in the current
or the following step as external forces and so on. 2 Theoretically, no special treatment
should be required when a virtual object is manipulated. In fact, like others the avatar
is only an object with characteristics like position, speed and acceleration where a part
of the external forces is determined by the operator. Figure 16.1 shows the architecture
of a simulator controlling a haptic device. We can observe that the collision detection
module makes it possible to determine the collisions received by the avatar, whereas the
next module resolves the collision and calculates the position and force data necessary
for the simulation and the haptic interface. The external forces, i.e. all the actions
taken on the avatar are calculated after some simulation. They are modified by a
control loop in order to ensure that the device is transparent and passive (refer to
chapter 9 “Control of a force feedback interface'' of this topic), and then recreated for
the operator via the haptic interface. However, as a part of the state of the manipulated
2 The mathematical formula of these forces is derived from physics and mechanics, mainly
non-smooth, when the constraints are taken into account explicitly.
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