Support for Cooperatively Controlled Objects in Multimedia Applications

ABSTRACT

Keywords

© 1997 Copyright on this material is held by the authors.

INTRODUCTION

There are a number of collaborative systems which encourage communication through common objects[5], tasks[4] or physical situations[1]. Groupkit[5] and Turbo Turtle[3], in particular, use telepointers and other "awareness widgets" to indicate to others where a user is working in the system. These systems do assist collaboration, but in many cases users still may work independently on a task, communicating infrequently to exchange files or merge objects.

We believe that there are some situations in which a common focus and close communication facilitate the learning process. We are developing a library of "cooperatively controlled objects" which are designed to encourage synchronous, complex, and collaborative interactions. The state of a Cooperatively Controlled Object (CCO) may be simultaneously manipulated, perhaps in complicated ways, by multiple users. Thus, a computer system which supports CCOs must provide input devices that are each controlled by a different user.

The components or "properties" of a CCO may be manipulated using general methods, such as constraints between user inputs and application objects. Fine-grain sharing, studied by Shen[6], is one method to implement an object shared in terms of its parts such that each part may be controlled by a different user. Although fine-grain sharing can offer users a clear delineation of responsibility and control for shared objects, it does not necessarily enforce synchronous manipulation by multiple users.

For example, a point may be controlled by decomposing it into its x and y coordinates which are modified by separate users as shown in Figure 1. The cooperatively controlled point in Figure 2 involves four users simultaneously altering the location and slope of two intersecting line segments using the endpoints. The location of the cooperatively controlled point is determined by the intersection of the two lines.

Figure 2. Cooperative control of the location of a point by four users

COIMAGE: Three Collaborative activities

Figure 3. The Collaborative Image Warper

The collaborative image warping activity, shown in Figure 3, charges the users to draw and manipulate warping-control line segments on the source or destination image. The segments are drawn individually, but they may be altered by one or both users simultaneously. Segments are translated by clicking and dragging on the middle of the line and are rotated by manipulating the location of the endpoints. When all the lines are in place, either user may begin the warping of the image. While the lines are controlled through a fine-grain sharing mechanism, we could easily modify this activity so that lines may only be rotated when both users are manipulating distinct endpoints, guaranteeing a simultaneous interaction.

Figure 4. The Collaborative Jigsaw Puzzle

In the collaborative jigsaw puzzle activity shown in Figure 4, the CCOs are the puzzle pieces. Each piece is controlled by a line segment. The centroid of the puzzle piece is constrained to the midpoint of a line segment. Two users adjust the location and rotation of each piece by manipulating endpoints of the segment.

Figure 5. A Collaborative Etch-A-Sketch Activity

What we call the Etch-A-Sketch™ activity allows the users to draw with one of three different cooperatively controlled pens. The simplest control, shown in Figure 5, allows each user to manipulate a slider, each of which corresponds to either the x or the y coordinate of the pen. A more difficult control constrains the location of the pen to be the midpoint of a line segment. This line may be manipulated in the same manner as in the two activities described previously. The most difficult control involves four users manipulating the pen as in Figure 2. This activity also may be timed. Once the clock begins, the users must keep the pen within the boundaries of a background object or time gets added to their total.

FUTURE WORK

CONCLUSIONS

REFERENCES

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