Is there a way to Union?

[williamsokol]

Hi, I was trying to union 2 rect's with this extension and I don't see any command for that.

I know I can do it manually selecting both objects and going Path->union. Is that something we can do with the extension right now?

[spakin]

Unfortunately, the inkex library, on which Simple Inkscape Scripting is based, does not provide a path-union function. Fortunately, there is an alternative: the non-destructive Boolean live path effect (Path → Path Effects… → Boolean operation in the Inkscape GUI).

It takes quite a bit of code to instantiate a non-destructive Boolean live path effect, but at least it can be done:

# Define a filter to make the target of the Boolean union invisible.  As
# far as I can tell, this *has* to have the ID "selectable_hidder_filter".
invisible = filter_effect(name='Visibility',
                          pt1=(-0.005, -0.005),
                          pt2=(1.005, 1.005),
                          color_interpolation_filters='sRGB')
invisible.add('Composite',
              src1='BackgroundImage',
              src2='SourceGraphic',
              operator='arithmetic')
invisible.get_inkex_object().set_id('selectable_hidder_filter')

# Create the target object, marking it invisible.
b = rect((50, 50), (150, 150),
         stroke='black',
         fill='cyan',
         filter=invisible)

# Instantiate a live path effect for Boolean union.  We use keyword
# arguments to preserve hyphens in key names.
b_ref = '#' + b.get_inkex_object().get_id()
union_args = {
    'operation': 'union',
    'operand-path': b_ref,
}
union = path_effect('bool_op', **union_args)

# Create the source object (which must be a path) and apply the live path
# effect to it.
a = rect((0, 0), (100, 100),
         stroke='black',
         fill='green').to_path()
a.apply_path_effect(union)

I hope you find that helpful.

[williamsokol]

Thank you very much! I was looking for a way to do this and was going down the route of using inkex.command.inkscape to call a union from the command line. It was looking impossible.

I can turn this code into a function and It will act effectively the same as a traditional union. Awesome

[williamsokol]

After working with it some, It seems like you cannot union multiple shapes together with the live path effect. If one is unioned the others will break off.

[spakin]

I just did a quick test in the Inkscape GUI, and I was able to union multiple shapes by chaining the Boolean operation. That is, I assigned a Boolean-union path effect to object A, pointing to object B. Then, I assigned a Boolean-union path effect to object B, pointing to object C. And likewise for a few more objects. Although I haven't yet tried this with Simple Inkscape Scripting, there's at least some hope you may be able to union multiple shapes together programmatically.