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devguide-21.html
Plugin Configuration
devguide-20.html
Plugins
devguide-23.html
Export Filters
Import Filters
Skencil uses import filters to read vector drawings from files.
Configuration Variables
For import filter configuration, Skencil uses the following variables:
type
The type must be
Import
. This identifier is defined in the
globals() dictionary.
class_name
A string containing the name of a Python class defined in the
module. See below for the interface this class has to provide.
rx_magic
A string containing a regular expression suitable for the re
module. This regular expression is matched against the first
line of the file. if it matches, the import mechanism assumes
that the filter understands the file's format and then procedes
to use that filter to load the file. So, if possible, this
regular expression should match those files the filter can
handle and only those.
While this method of identifying files is not really sufficient
to handle all file types, it works well enough for now. In the
future we will probably have to extend this mechanism.
tk_file_type
A tuple containing two elements. The first is the name of the
file format presented to the user in the file open dialog. The
second element is eithe a string or a tuple of strings. Each of
the strings defines a file name extension used for that
filename.
Examples:
#tk_file_type = ('Skencil Document', '.sk')
#tk_file_type = ('PostScript file', ('.ps', '.eps'))
unload
(optional)
A boolean. True means that the filter module should be unloaded
after use, false means that it shouldn't be unloaded. If the
module is unloaded it will be imported again the next time the
filter is needed. Infrequently used filters should set this to
true, frequently used filters (like the filter for Skencil's own
format) should set it to true.
If omitted, it defaults to false.
It's a good idea to set this variable to true at least while
developing a filter because that way the filter will be
automatically reloaded when the source file changes.
format_name
The name of the format as a string. This name is currently used
internally to find out whether a document was loaded from a file
in Skencil's format or from a different format (in the latter
case `Save' is treated like `Save As...', i.e. the user has to
provide a filename).
standard_messages
(optional)
A boolean indicating whether the messages in the plugin are
standard messages that are defined in Skencil's message catalogs.
For third-party plugins this should be omitted.
The Class Interface
External Interface
The interface a loader class presents to the document loading mechanism
is quite simple. The loading mechanism works roughly as follows:
Read the first line of the file
Match it in turn against all the regular expressions
defined for import filter plugins (defined by the
#N4
rx_magic variable
).
If a match is found, instantiate the plugin's class
(defined by the
#N3
class_name variable
) with
three positional parameters
file
,
filename
and
match
.
file
is the open input file object, positioned just after
the first line.
filename
is the name of the file.
match
is the match-object returned from regular expression
match.
If possible, filters should read the input file sequentially and
not use seeks. Skencil automatically pipes gzipped files
through gzip and in that case the file object is actually a
pipe, so seeks would be impossible. If a filter needs to access
the first line it can do so by using
match
.string or by
defing suitable groups in the regular expression.
Call the instance's Load() method (without arguments).
This method does the actual work and returns an instance of the
document class.
Call the instance's Messages() method without arguments.
The return value is expected to be a list of strings with
messages that are usually presented to the user by the UI.
If the
#N5
unload configuration
variable
is true, unload the plugin's module.
Common Base Classes
To make things easier, Skencil defines some base classes that plugins
can inherit,
LoaderWithComposites
and, derived from
that,
#N10
GenericLoader
and
SimplifiedLoader
, derived in turn from
GenericLoader
.
GenericLoader
The class
GenericLoader
provides a default implementation of the
constructor, a mechanism for warning and error messages and methods to
easily create standard objects like rectangles, ellipses and groups.
GenericLoader
defines these methods:
__init__(
file
,
filename
,
match
)
Assign the arguments to
self.file
,
self.filename
and
self.match
respectively.
document()
Start the construction of a document. This method must be called
before any other of the object creation methods are called.
layer([
name
])
Start a new layer. This method must be called after calling
#N12
document
and before any of the other object
creation methods.
name
is the name of the layer. If omitted, it defaults to
"Layer 1".
begin_group()
Start a new group. Groups can be arbitrarily nested. Each call
to
begin_group
must have a corresponding call to
#N15
end_group
.
end_group()
End the current group.
rectangle(
m11
,
m21
,
m12
,
m22
,
v1
,
v2
[,
radius1
= 0][,
radius2
=
0])
Create a new rectangle object and append it to the current
compound object.
The first six positional parameters (
m11
,
m21
,
m12
,
m22
,
v1
,
v2
) define a
transformation matrix that transforms the unit square (opposite
corners (0,0) and (1,1)) onto the rectangle.
radius1
and
radius2
define the rounded corners.
For more details see the documentation for the class
devguide-18.html#N2
Rectangle
ellipse(
m11
,
m21
,
m12
,
m22
,
v1
,
v2
[,
start_angle
= 0.0][,
end_angle
= 0.0][,
arc_type
= ArcPieSlice])
Create a new ellipse object and append it to the current
compound object.
The first six positional parameters (
m11
,
m21
,
m12
,
m22
,
v1
,
v2
) define a
transformation matrix that transforms the unit circle (center
(0,0) and radius 1) onto the ellipse.
start_angle
and
end_angle
, if given, define the
start end end angles for pie slices, arc and chords.
arc_type
defines whether and how the arc of an incomplete
ellipse is closed. Valid values are
ArcArc
,
ArcPieSlice
and
ArcChord
. These constants are defined
in
Sketch.const
For more details see the documentation for the class
Ellipse
bezier(
paths
)
Create a new bézier object in the current compound object.
paths
must be a tuple of
devguide-8.html
curve
objects
.
devguide-21.html
Plugin Configuration
devguide-20.html
Plugins
devguide-23.html
Export Filters
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