8.3 PSEUDO-TACTILE FEEDBACK
PTF is the combination of sight, sound, and control movement effects that serve as a
substitute for the sense of touch. This is useful in manipulating real-world objects.
The simplest form of substitution is to use sight for touch. For example, a tic mark
might appear or an object face might highlight when the user drags the target object
into some desired position. This is simply relational feedback, which was already
discussed above. A more sophisticated approach, which gets to the heart of PTF,
tightly couples control dynamics with sight and sound cues to impart a stronger suggestion
of natural feel. For instance, in the furniture layout example, a user might
drag a desk that is in some arbitrary orientation toward a wall. When the desk hits the
wall, the desk highlights and a soft "collision" sound effect plays. As the user continues
to drag the mouse toward the wall, the desk begins to turn, as would a real desk if
dragged in a similar fashion, while an undertone of "scraping" is heard. If the user
persists with the drag, the desk will eventually turn flush with the wall and stop, at
which point the desk highlight flashes once, returns to normal, and a gentle sound
effect of finality plays. The intent of these effects is to evoke in the user impressions
that the objects and their interactions are real— or at least as real as they might seem if
used in a movie— with visual and audio feedback providing idioms that reinforce a
sense of feel.
This section covers these and other variations on PTF techniques, which are summarized
in table 8. 3, and illustrated in figure 8. 13. Some emphasize visual and sound
effects; others emphasize object and control dynamics. As with many of the other techniques
presented throughout this part of the book, you can mix and match the PTF
variations as you see fit.
Table 8. 3 Summary of PTF drags and grips
| Marked drag |
- Sight and sound feedback only; no change in control dynamics.
- Weak tactile effect; relational feedback indicates proximity or alignment.
|
| Sticky drag |
- During drag, object stutters to indicate proximity and to help alignment.
- Strong tactile effect; object stays where left; can require forced cursor movement; can interfere with precise adjustments.
|
| Snap drag |
- At drag end, object jumps into alignment.
- Weak tactile effect; unexpected object jump; can interfere with precise adjustments.
|
| Solid drag |
- Dragged objects are solid.
- Prevents confusion of objects intersecting; can interfere with object layout.
|
| Strong grip |
- During drag, no slippage or twisting of object upon collision.
- No real-world dynamics.
|
| Weak grip |
- During drag, object is allowed to slip and twist upon collision.
- Effect can be unexpected and unappreciated.
|
8.3.1 Marked drag
Starting with the simplest form of PTF, marked drag relies on sight and sound effects
only, with no change in control dynamics. While the user is dragging an object, relational
feedback such as tic marks might appear alongside the target object and its
Figure 8. 13 Examples of PTF drags and grips
neighbors as alignment of various sorts occurs. Variations might use outline feedback
to highlight the matching objects and object parts (vertex, edge, and face). Information
feedback, like callouts, might appear to provide further detail about the type and
location of the relationship achieved. In addition to its normal supporting role, sound
might help to differentiate the type of relationship achieved, with variations on the
basic "alignment achieved" sound effect indicating different types of alignments, such
as edge, face, or midpoint.
Variations on marked drag might also include feedback regarding spatial proximity.
For example, skirts and rulers might appear on the target object when near other
objects, which serve both as a forewarning of collision and as assistance in performing
precision object placement. In these situations, sound effects can reinforce warnings
of imminent and actual collision. Additionally, the pitch of a mild tone or the frequency
of a soft click could indicate the target's proximity to alignment or collision.
8.3.2 Sticky drag
People are naturally sensitive to discontinuities between what the hand does and what
the eye sees. Taking advantage of this sensitivity is what really sets PTF apart from simple
relational feedback. Sticky drag is one of the simpler PTF techniques that benefits
from such eye-hand control effects. With sticky drag, while the user is dragging an
object, it will seem to stutter or stick slightly when it reaches some predefined position,
or aligns or collides with another object. The effect is not unlike a detent in a multipostion
knob. For example, to help the user during layout, an alignment grid might be
defined for position, and angular graduations might be defined for rotation. Objects
would slide and rotate smoothly until they reached a grid line or an angular detent.
The movement sticks there until the user overdrags the object or starts a new drag.
The degree of stickiness might vary depending on the situation. A small overdrag
might be needed for a graduation detent, a large one for object-to-object alignment,
and a new drag might be required after a collision. A variation on simple overdrag is
to use a more pronounced gesture, such as a flick or jerk, to resume object movement.
As with marked drag, sound effects can reinforce the tactile sensation and provide a
feeling of proximity. Outline feedback can highlight the aligned or colliding objects
and object parts.
The tactile effect of sticky drag is more pronounced than that of marked drag
because marked drag relies solely on sight and sound whereas sticky drag also affects
eye-hand coordination. This can be good, but it can also be bad. Techniques that
affect the drag dynamics can seem unexpected to users if they are not familiar with the
effect. Like any good idiom, this one can be quickly learned by the user. Another draw-back
of sticky drag is that the mouse cursor must be forcibly moved by the system to
affect the stutter. Some designers reject such forced cursor movement on principle.
A more serious problem is that sticky drag can interfere with precise object placement
when the object is near a sticky point. One possible remedy is to introduce hysteresis
into the stickiness so that the drag doesn't immediately stick to the same point.
A simpler but more direct way around this problem is to allow the user to momentarily
disable the stickiness, such as by pressing a modifier key during a drag. Another possibility
is to let the user perform fine adjustments with the arrow keys, which are not
subject to the sticky effect. Although such keyboard-based alternatives sound good and
can be effective, trying to let the user know they exist and how to use them is another
matter, which is often the problem when keyboard controls are used.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
|
