19.2.3 IntuitiveDragMapper class
Conversion from 2D input space to 3D source space is performed by the Intuitive-DragMapper
class. It uses an IntuitiveDragMapperPlugin to handle the details of
translating between spatial coordinate systems and event types. Subclasses of this
plug-in are provided to support DRM and several flavors of WRM. Each handles
acquisition and use of source space reference nodes differently. Specifics will be covered
in later sections on DRM and WRM. The internal interface between the mapper
and its plug-in are similar to those between the InputDragMapper class and its plug-in,
the InputDragMapperPlugin.
By definition, input to source mapping is a point mapping, meaning that the
input position is mapped to a source position using a point transformation rather than
a vector transformation. The distinction is subtle, but important when setting up an
input drag filter chain to feed an intuitive Mapper. The mapper's input event interface
is InputDragTarget, and its output event interface is SourceDragTarget.
SourceDragTarget interface
The SourceDragTarget interface is essentially a 3D version of the 2D InputDragTarget
interface, including methods for drag start, drag continuation, and drag
stop. In place of a source display, the methods use a source scene graph node to define
the local source space. The corresponding event splitter is the SourceDragSplitter class.
19.2.4 SourceDragFilter class
Source drag filtering is quite similar in form and function to that of input drag filtering.
The SourceDragFilter class is the host for all filtering operations, with a plug-in
giving it a personality. The plug-in base class, SourceDragFilterPlugin, has the same
basic internal interface and is used the same way by its host as the InputDragFilterPlugin
described for basic control interpretation. It also has the same limitation of
being able to handle only the simplest forms of filtering, which do not involve state
or time-dependent processing.
SourceDragFilterPlugin subclasses
Although all the same filter operations could be provided as for input drag filtering,
the framework provides the two most common ones. The AbsoluteSourceDragPlugin
class provides absolute filtering, with a 3D point specifying the origin of the drag
operation The RelativeSourceDragPlugin class performs relative origin filtering, with
the 3D origin being determined by the starting point of the drag. No source drag
enable filter is provided because drag enabling can be handled from the input drag
space— in a POCS there is no 3D mouse sensor to directly generate source drag events.
19.2.5 SourceDragMapper class
The SourceDragMapper class handles the conversion from source space to actuation
space. Both the source-to-target and the target-to-actuation spatial conversions
are included in this Mapper. A method is provided to specify whether or not drags
are cumulative. Consistent with other mappers in the framework, a plug-in, the
SourceDragMapperPlugin class, handles the rest of the mapping details. The internal
interface between the mapper and the plug-in is similar to that in the InputDragMapper
class.
By definition, source-to-target mapping is a vector mapping, meaning that the
source position value is treated as a vector, with direction and magnitude being transformed
instead of position. As with intuitive mapping, the distinction is subtle but
important when building a source drag filter chain to feed a source Mapper. The
mapper's input event interface is SourceDragTarget, and its output event interface
is ActuationTarget.
DirectSourceDragPlugin class
The framework provides only for direct source mapping, with the DirectSourceDragPlugin
class. It includes methods for specifying source value scaling and target value
offset. All mapping is direct and by dimension, similar to that for input drag map-ping,
but here two separate mappings are used: one for source-to-source dimension
mapping, and the other for target-to-actuation dimension mapping. Mapping occurs
in three steps. First the source-to-source dimension mapping is applied to the source
value, then the source value is spatially transformed to the target space, and finally the
target-to-actuation dimension mapping is applied to the target value.
AxisAngleSourceDragPlugin class
To handle source drag rotations, the framework provides the AxisAngleSourceDragPlugin
subclass of DirectSourceDragPlugin. To accommodate the generalized map-ping
from source to target space, a simple fixed-axis rotation can not be used. Instead,
a fixed rotation axis is defined relative to the source space, and the axis is spatially
transformed as a vector to the target space. The angle of rotation defined by the
source value, however, is not spatially transformed as would normally be done in the
superclass. Instead, it is mapped directly, by dimension, from source to actuation
spacing using the combination of the source and target mappings.
Stop by in one week for the next installment!
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