Graphics Reference
In-Depth Information
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Gravity (external effects on objects).
The velocity of a ball is con-
stantly changing due to the defined gravitational force.
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Status bar (application-state echo).
The user can monitor the appli-
cation state by examining the information in the status bar. In our
application, the number of balls currently on the screen is updated in
the status bar.
Our application starts with an empty screen. The user clicks and drags to
create new balls with different radii and velocities. Once a ball travels off of the
screen, it is removed. To avoid unnecessary details, we do not include the drawing
of the motion trajectories or the velocity vector in our solutions. Notice that a
slider bar communicates its current state to the user in two ways: the position of
the slider knob and the numeric echo (see
Figure I.2
)
.
We have now described the behavior of a simple interactive graphics appli-
cation. We can begin learning the concepts that support the implementation of
this type of application. We concentrate on issues concerned with interaction and
software engineering practices.
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