Applications Area Working Group F. Echtler
Internet-Draft Munich Univ. of Applied Sciences
Intended status: Informational March 7, 2011
Expires: September 8, 2011
GISpL: Gestural Interface Specification Language
draft-echtler-gispl-specification-00
Abstract
This document introduces GISpL, the Gestural Interface Specification
Language. GISpL enables the unambiguous description of gestures used
in human-computer interfaces. This includes gestures on touch and
multi-touch screens, with digital pens, with hand-held controllers or
in free air. A matching engine analyzes motion data produced by the
input device(s) and triggers registered gestures.
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described in the Simplified BSD License.
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1. Introduction
This document describes GISpL (Gestural Interface Specification
Language), a formal language for describing human-computer interfaces
which use gestures. The term "gesture" is used in a very wide sense
here, meaning any motion of the user which can be captured by an
input device.
1.1. Motivation
As novel types of human-computer interfaces such as multi-touch
screens, digital pens, hand-held controllers or even free-air
gestures become more and more common, so does the number of special-
purpose applications built to interact with these devices.
Using a dedicated formal language to describe the various types of
gestural interaction which are possible with an application has
advantages for various distinct groups:
Users End users of gestural applications benefit in two ways: the
behavior of such applications becomes more consistent across
different platforms and the users are given the option to
modify the behavior to suit their needs.
Researchers When the behavior of a gestural interface is specified
formally, it is easier for user interface researchers to
compare different interfaces. Also, prototypical
implementations of such interfaces are easier to modify and
adapt during the design, development and evaluation cycle.
Developers Since the formal specification enables a dedicated
matching engine to perform the actual detection and matching
of gestures, developers are spared tedious tasks such as
constant reimplementation of basic gesture matching
algorithms.
1.2. Design Considerations
GISpL serves two purposes:
o describe what motions the users have to execute in order to
trigger a certain response
o deliver information about the actual execution of these motions to
the application
Moreover, GISpL should be usable across a very wide range of
platforms, even unconventional ones. One important example is the
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Firefox web browser which has recently acquired the capability to
deliver multi-touch events to web applications.
Consequently, the requirements regarding GISpL are:
o must be human-readable
o must be machine-readable
o must be supported on a wide range of platforms
o must be lightweight for low-latency network transmission
Therefore, the decision was made to base GISpL on JSON [RFC4627].
Compared to XML, JSON gives a better balance between readability for
humans and code size. It is supported in nearly all programming
languages and platforms.
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2. Specification
GISpL consists of three core elements: regions, gestures and
features.
For the full formal ABNF specifictation, please see the appendix.
This section will use a relaxed syntax for easier readability, with
rule names enclosed by angle braces < >. JSON-related markup ( { } ,
[ ] "" ) will be reproduced verbatim.
2.1. Definitions
In the context of GISpL, the terms _input object_ and _input event_
will be used. An _input object_ is any physical object which is
detectable by the input hardware, such as a mouse, a Wiimote or the
user's hand. Input objects are classified into one of 32 categories
as given in the appendix. Every input object is given a unique ID
number according to the capabilities of the hardware. I.e., a
uniquely identifiable tangible object always has the same ID, while
anonymous touch points on an interactive surface will have IDs so
that each touch point is uniquely identifiable during the duration of
the touch. An _input event_ is a single spatial measurement
regarding the position (and optionally, orientation, dimensions etc.)
of an input object as captured by one or more of the sensors used.
2.2. Region
Regions define spatial areas in which a certain set of gestures is
valid and which capture motion data that falls within their
boundaries. Regions are defined in one of two reference coordinate
systems:
o A 2D screen coordinate system where the x and y coordinates range
from 0.0 to 1.0 across the physical extension of the user's
screen, with the origin being in the lower left corner. This is
indicated by the region flag "poly". The list of boundary points
is interpreted as a closed polygon in the x-y plane. The z
coordinate is not used.
o A 3D metric coordinate system with an arbitrary reference point as
origin (usually defined by the input device). This is indicated
by the region flag "hull". The list of boundary points is
interpreted as defining the convex hull of the region.
Regions are managed in an ordered list. Arriving input events are
checked against this list, starting from the first element. If the
position of the input event falls within the boundaries of the region
_and_ if the bit in the filter bitmask which corresponds to the
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category of the input event is set, the the input event is captured
by the region. Captured events and their history are subsequently
used to check whether one or more of the gestures attached to this
region have been triggered.
point = [ <number>, <number>, <number> ]
pointlist = [ null/<point> *( , <point> ) ]
regionflags = "poly" / "hull"
region = {
"id":<string>,
"flags":<regionflags>,
"filters":<number>,
"points":<pointlist>,
"gestures":<gesturelist>
}
2.3. Gesture
Gestures appear in two variants: either as gesture specifications
(describing what motions the user has to execute for a certain
effect) or as gesture events (describing a) the fact that a matching
motion event just took place and b) the motion data which triggered
the event).
Whether a gesture object is a gesture event can be determined from
looking at the flags. Should they contain the string "result", then
it is a gesture event and the features composing this gesture will
contain valid data in their "result" array. Otherwise, the object is
a gesture specification and the features will contain valid data in
their "constraints" array.
When a gesture has the "oneshot" flag, then it can only be triggered
once by a given set of input IDs. Repeated triggering is only
possible when the set of IDs captured by the containing region
changes.
When a gesture has the "default" flag set, it is added to a pool of
default gestures. When a gesture specification with an empty feature
list is encountered, then the name is looked up in the default
gesture pool and if a match is found, the feature list is copied from
the default gesture. Otherwise, the empty gesture is ignored.
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gesturelist = [ null/<gesture> *( , <gesture> ) ]
gestureflag = "oneshot" / "default" / "result"
gestureflags = [ null/<gestureflag> (* , <gestureflag> ) ]
gesture = {
"name":<string>,
"flags":<gestureflags>,
"features":<featurelist>
}
2.4. Feature
are the building blocks of gestures and are atomic mathematical
properties of the raw motion data, such as the average motion vector
or the diameter of the convex hull of all motion points.
featurelist = [ null/<feature> *( , <feature> ) ]
featureitem = <point>/<number>
itemlist = [ null/<featureitem> *( , <featureitem> ) ]
feature = {
"type":<string>,
"filters":<number>,
"constraints":<itemlist>,
"result":<itemlist>
}
A feature is classified by its type, a filter bitmask for input
events as described in Section 2.2, a type-specific list of
constraints and a type-specific list of results. Depending on
whether the containing gesture is a "result" gesture or not (see
Section 2.3), either the constraint list or the result list will be
empty. All temporal relations (such as motion vector) are expressed
relative to a time unit of one sensor frame, i.e. for a sensor setup
running at 60 Hz, the temporal unit will be 16.66 ms.
Features are divided into two groups. The first one are _single-
match_ features, which will only generate a single result instance
regardless of the number of input objects.
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+----------+-------------+----------+-------------------------------+
| Feature | Constraint | Result | Description |
| Type | Types | Types | |
+----------+-------------+----------+-------------------------------+
| Motion | <point>, | <point> | Average motion vector, lower |
| | <point> | | and upper limits per |
| | | | component |
| | | | |
| Rotation | <number>, | <number> | Relative rotation angle in |
| | <number> | | rad, lower and upper limits |
| | | | |
| Scale | <number>, | <number> | Relative size change, lower |
| | <number> | | and upper limits |
| | | | |
| Path | <point> *(, | <number> | Match for template path |
| | <point>) | | |
| | | | |
| Count | <number>, | <number> | Number of input objects, |
| | <number> | | lower and upper limits |
| | | | |
| Delay | <number>, | <number> | Number of frames since first |
| | <number> | | object entered, lower and |
| | | | upper limits |
+----------+-------------+----------+-------------------------------+
Single-Match Features
Table 1
The second group of features are _multi-match_ features, which will
potentially generate one result instance for each input object
(depending on the constraint values).
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+-----------------+--------------+-----------+----------------------+
| Feature Type | Constraint | Result | Description |
| | Types | Types | |
+-----------------+--------------+-----------+----------------------+
| ObjectID | <number>, | <number> | Match range of |
| | <number> | | unique IDs (e.g. for |
| | | | tangible objects) |
| | | | |
| ObjectParent | <number>, | <number> | Match range of |
| | <number> | | unique parent IDs |
| | | | (e.g. for fingers |
| | | | belonging to |
| | | | specific user) |
| | | | |
| ObjectPosition | <point>, | <point> | Position, lower and |
| | <point> | | upper limits per |
| | | | component |
| | | | |
| ObjectDimension | <point>, | <point>, | Object dimensions, |
| | <point>, | <point>, | lower and upper |
| | <point>, | <number> | limits per component |
| | <point>, | | (major axis, minor |
| | <number>, | | axis, size) |
| | <number> | | |
| | | | |
| ObjectGroup | <number>, | <number>, | Match group of input |
| | <number>, | <point> | objects (min. count, |
| | <number> | | max. count, max. |
| | | | radius). Result = |
| | | | count/centroid |
+-----------------+--------------+-----------+----------------------+
Multi-Match Features
Table 2
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3. Runtime Behavior
This section details the behavior of the gesture matching engine.
The following steps are performed every time an input event has been
received:
1. ...
2. ...
The following steps are performed every time after a full set of
input events has been received:
1. ...
2. ...
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4. Examples
For illustration purposes, this section gives some usage examples of
GISpL.
TBD
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5. Security Considerations
Gesture events, if intercepted while in transit over the network, may
disclose private data about the users' actions. Consequently, they
should preferably be transmitted over secure channels such as private
networks, VPNs or SSL-encrypted links.
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6. IANA Considerations
This document has no actions for IANA.
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7. References
7.1. Normative References
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
7.2. Informative References
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
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Appendix A. Formal GISpL Specification
The following formal specification of GISpL is given in ABNF
[RFC5234]. JSON-related rule definitions (e.g. <number>, <string>
...) are to be found in [RFC4627].
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quote = quotation-mark
point = begin-array
number value-separator number value-separator number
end-array
item = point / number
itemlist = begin-array item *( value-separator item ) end-array
pointlist = begin-array point *( value-separator point ) end-array
gesturelist = begin-array gesture *( value-separator gesture ) end-array
featurelist = begin-array feature *( value-separator feature ) end-array
filters = quote "filter" quote name-separator number value-separator
regionid = quote "id" quote name-separator string value-separator
regionflags = quote "flags" quote name-separator
( ( quote "poly" quote ) / ( quote "hull" quote ) )
value-separator
gesturename = quote "name" quote name-separator string value-separator
gestureflag = ( quote "oneshot" quote ) / ( quote "default" quote )
gestureflags = quote "flags" quote name-separator
begin-array gestureflag
*( value-separator gestureflag )
end-array value-separator
featuretype = quote "type" quote name-separator string value-separator
results = quote "result" quote name-separator itemlist
constraints = quote "constraints" quote name-separator
itemlist value-separator
feature = begin-object
featuretype constraints results
end-object
gesture = begin-object
gesturename gestureflags featurelist
end-object
region = begin-object
regionid regionflags filters
pointlist value-separator gesturelist
end-object
Figure 1
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Appendix B. Input Event Types
TBD - see TUIO 2.0 spec
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Author's Address
Florian Echtler
Munich Univ. of Applied Sciences
Lothstr. 64
Munich 80336
Germany
Phone: +49 89 1265 3736
Email: floe@butterbrot.org
URI: http://floe.butterbrot.org/
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