El proceso de trabajo en la esquila de lana

The Black Hole is the interface element for deletion – similar in function to the Trash or Recycle Bin on modern computing desktops. In our interface for manipulating digital photographs, we wished to support a reversible deletion method that provided continuous feedback, rather than having objects simply disappear. In addition, clutter is of particular concern for tabletop interfaces, and the Black Hole is one of our techniques for dealing with it.

The Black Hole is a semi-translucent image with swirls as shown in Figure 4.3. It is always shown in front of other photos and can be manipulated as a regular photo – it may be moved and resized – but some operations are restricted. For example, the Black Hole cannot be duplicated or be moved into any private area.

The Black Hole is an object with a sphere of influence, that affects the size of photos within and around it (i.e. that overlap the Black Hole photo). This notion is inspired by analogy with astronomical phenomenon. Photos closer to the centre of the Black Hole are proportionally smaller than photos on the fringes. Very close to the centre, the photo is hidden. Figure4.3 shows a user moving a photo into the Black Hole. As the photo is

moved from the right to left, the photo gets smaller as it moves closer to the centre. This

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Figure 4.3: Putting an image into the Black Hole

Note that, as for rosize, we do not want the point of contact on the image to slip. An additional mathematical step means that the decrease in size as an object is moved towards the Black Hole occurs centred on the point of contact, rather than the centre of the image, as for rosize.

The Black Hole helps support the ability to free screen space and dispose of unwanted images. This is somewhat like the Trash can on many desktop user interfaces, but the Black Hole also satisfies a number of natural interaction rules that improve its usefulness for collaborative interaction, while satisfying our design drivers:

• photos placed in or near the Black Hole can be recovered (photos are not deleted permanently),

• photos can be partially removed (i.e. out of the way, but easily retrieved),

• photos maintain a physical-virtual coupling as they progress from normal 7→ partially hidden 7→ hidden 7→ retrieved (i.e. giving continuous feedback),

• photos influenced by the Black Hole do not suddenly appear or disappear,

• photos placed in or near the Black Hole remain bound to it (e.g. when the Black Hole is moved), and

• as the Black Hole is resized, the photos within its sphere of influence change their size accordingly (the photos are not moved, but the amount of image within the Black Hole will change, resulting in a change of size).

An object placed partially in a Black Hole can be seen in Figure 4.2, indicated À.

There are a number of techniques to recover objects from the Black Hole. If the object is still on the fringe, it may simply be be moved out, provided some of the photo pokes

out from underneath the Black Hole. If no part of the image is selectable, the Black Hole

fringe become larger; it can then be moved away. However, the Black Hole cannot be made arbitrarily small, or it would be too hard to re-select, so we have explored other techniques.

When private spaces are enabled, a user can also attempt to move the Black Hole into their personal space. The latter technique is based on the premise that, while the Black Hole cannot be moved into your personal space, the photos within it can. Thus the Black Hole gets stuck on the border of your personal space, while the photos within it gradually come out.

A third technique to retrieve objects from the Black Hole does not rely on private spaces – it uses flick and is described below. The Black Hole can also be flipped. A planned feature for future work is to perform a layout of objects inside the Black Hole when it is flipped over, allowing them to be removed.

Implementation details for the Black Hole are in Section5.2.4.4. 4.3.1.1 Moving the Black Hole

If a user wishes to move the Black Hole, they do this simply by dragging it. The Black Hole and all its contents (including items on its fringes, which may still be visible) are moved to the new location, maintaining their relative positions. As the Black Hole moves, photos it comes near are affected by the Black Hole, if the centres of those photos enter the fringe. If the Black Hole is then released, those objects are captured, allowing the Black Hole to be used something like a vacuum cleaner on the virtual environment.

4.3.1.2 Dwelling on the Black Hole

We noted in Section4.2.6that objects may provide their own actions when they are dwelled upon. Dwelling on the Black Hole initially causes all images in (or partially within) the Black Hole to be deleted permanently, so that they cannot be retrieved. This allows the system resources (e.g. memory) used for those images to be reclaimed. However, this is not usually required for regular photo browsing: Cruiser has other, automatic strategies to conserve and reuse system resources. Also note that the original files on disk are never deleted – such a level of file management is not a focus at this stage of our interface development.

A dwell on the Black Hole also affects all images on the interface, by gravitating them towards the Black Hole – each object will begin to move along a straight line towards the centre of the Black Hole. The speed of movement accelerates – increasing in speed the longer the Black Hole is dwelled upon. This is a significant global action to perform, but as it begins small and gives very obvious feedback, it is easily stopped simply by releasing the Black Hole.

4.3.1.3 Flicking around the Black Hole

We want to allow users to put objects into the Black Hole, even when the Black Hole is not easily within reach. A flick gesture that started moving an object towards the Black Hole could allow objects to be quickly deleted without requiring the full move operation to be performed.

To achieve this, around the Black Hole, flicked images (§4.2.3– i.e. those with a current momentum) are subject to a gravitational force that causes them to accelerate towards the centre of the Black Hole. This has the result one might expect of orbiting astronomical bodies in the physical world.

We continue to apply the wormhole effect (reducing the size of the image), and maintain the incident momentum as it approaches the Black Hole. But, as we wish to avoid a perpetual orbit in most cases, when the component-wise change in velocity is in the opposite direction to the current velocity, the acceleration towards the centre of the Black Hole is

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increased. This will cause the path of object to favour spiralling in to the centre of the Black Hole (when not aimed directly towards it).

We also capture objects when they enter the centre region of the Black Hole. Thus, while objects with large momenta may sling shot out of the Black Hole, images aimed directly at the centre of the Black Hole, will be caught. The analogy here is that an object has collided with the body at the centre of the Block Hole’s sphere of influence.

Images with momentum may be flicked to the Black Hole, whereupon they can be

sucked in. This would allow, for example, a user to delete an object even if the Black Hole

is not in reach. The manner is modelled on gravity and physics so we maintain feedback while the image is deleted. Thus, an object does not just disappear when it hits any part of the Black Hole, and neither does the flick need to be accurate – any flick that would cause the image to pass though any region of the screen occupied by the Black Hole will be influenced. If the flick is too hard, however, it will continue past the Black Hole, rather than being sucked in.

Combined with flicking, a new technique for removing items from the Black Hole is possible. A quirk of the caching techniques used to optimise performance means that objects can also fall out of the Black Hole if it is flicked. The Black Hole does not gain momentum. Instead, if it is moved quickly and released, some of the objects within it are “left behind” and move to the Black Hole fringes, allowing them to be removed. Usually

multiple flicks are required to get images all the way out.

4.3.1.4 Black Hole Example

Consider the following scenario, a user plugs their digital camera into our interface. It holds a large number of photos taken from a recent holiday, so we load an object containing thumbnails for those photos. Sometimes, the thumbnail is insufficient quality to judge whether an image is the one desired to discuss, or to decide between two closely related photos. Dragging a thumbnail off the object causes a higher-quality copy of the thumbnail to be created. However, the user decides that they no longer need this copy, so they wish to delete it.

On a traditional computing interface, the user might drag the icon to Trash, but in a virtual environment, this has a number of problems. The Trash is usually located at a fixed position on the display; on a physically large virtual interface a user might not be able to reach this object, and so they may wish to flick it in the direction of the Trash. Alternatively, they may wish to move the trash object around the environment. There may be multiple users and the Trash may only be oriented or easily accessible by a single user. Opening the Trash to retrieve something might be impractical. Offering a confirmation dialogue to confirm deletion, or a context menu to move an item to Trash might be impractical. The Trash may be obscured and a user might inadvertently move an item over the Trash, accidentally deleting it. An object may be displayed on screen much larger than the Trash object, and without a mouse cursor, it might not be clear how to indicate that something should be moved to the Trash. We may also wish to support the user in partially hiding the image – this can be accomplished by moving the object onto the edge of the Black Hole.

To delete the photo using the Black Hole, the user drags the virtual object (e.g. with a finger or stylus) towards the Black Hole. Once the user’s finger (i.e. not the centre of the image; regardless of where it was touched) is within the influence of the Black Hole it begins to reduce in size. As the user’s finger gets closer to the centre of the Black Hole, the image gets smaller, until it can no longer be seen; at the centre of the Black Hole. Alternatively, if the user notices the reduction in size, and decides they do not actually want to delete/hide the image, they can take it back out immediately.

The Frame, selected, has been just been “dwelled” upon, and the new image can be seen expanding from the centre of the Frame. Hand icon indicates touch point – it does not appear in the interface.

Figure 4.4: The Frame, as it copies a photo