InteropGrabBag in LibreOffice Writer

FOSDEM 2014 (https://fosdem.org/2014/schedule/event/interopgrabbag_in_libreoffice_writer/), Brussels

Transcript

1. InteropGrabBag in
   LibreOffice Writer
   Miklos Vajna
   2014­02­01
   

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2. Filter problems
   

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3. 3 / 15
   FOSDEM 2014 | Miklos Vajna
   What is a filter problem?
   ● Filters map between an input/output
   stream and the document model
   ● A given filter: given file format
   ● If a feature in a file format is not
   roundtripped perfectly through the
   document model
   

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4. 4 / 15
   FOSDEM 2014 | Miklos Vajna
   Case #0: feature is already in core
   ● RTF import,
   groupshape support
   

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5. 5 / 15
   FOSDEM 2014 | Miklos Vajna
   Case #1: Implement the feature in
   core
   

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6. 6 / 15
   FOSDEM 2014 | Miklos Vajna
   Case #2: Import the result of the
   feature in the filter
   ● E.g. Table styles, document themes
   ● SmartArt import
   ● On import, apply the result of that as
   direct formatting
   ● Better, than nothing, but no real editing
   can be performed
   

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7. InteropGrabBag
   

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8. 8 / 15
   FOSDEM 2014 | Miklos Vajna
   Case #3: Just preserve it
   ● If a feature is completely unsupported by
   core, it makes sense to first just preserve it
   ● Use case:
   ● Long document
   ● Full of complicated features
   ● Just want to correct a typo
   

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9. 9 / 15
   FOSDEM 2014 | Miklos Vajna
   We do it for ODF already
   ● css::xml::ParaUserDefinedAttributesSupplier
   ● css::xml::TextUserDefinedAttributesSupplier
   ● css::xml::UserDefinedAttributesSupplier
   ● “The idea behind this property is that a
   parser can throw away all attributes that it
   cannot handle by itself […] can be written
   back without loss.”
   ● WW8 as well:
   SwTOXBase::maMSTOCExpression
   

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10. 10 / 15
    FOSDEM 2014 | Miklos Vajna
    Why a new API?
    ● Need separate storage
    ● ODF foreign format
    →
    – Would need manual mapping anyway
    ● Need a more flexible data structure
    ● UserDefinedAttributes is just a string­string map
    ● We want to store nested structures as well
    

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11. 11 / 15
    FOSDEM 2014 | Miklos Vajna
    The InteropGrabBag API
    ● New SfxPoolItem: SfxGrabBagItem
    ● Writer: RES_{CHR,PAR}ATR_GRABBAG, etc.
    ● UNO: InteropGrabBag property
    ● Type: css::beans::PropertyValues
    – Effectively a string­any map
    

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12. 12 / 15
    FOSDEM 2014 | Miklos Vajna
    A set of bags
    ● Each UNO object may implement it,
    currently supported:
    ● css::document::OfficeDocument
    ● css::drawing::Shape
    ● css::style::CharacterProperties
    ● css::style::ParagraphProperties
    ● css::style::Style
    ● css::text::BaseFrameProperties
    

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13. 13 / 15
    FOSDEM 2014 | Miklos Vajna
    The danger of hidden properties
    ● Problem: e.g. paragraph border is not
    supported, hidden “big black border”
    property
    ● User copy&pastes it elsewhere
    ● Result: pasted paragraph still has that
    property, probably not wanted
    ● Solution: clear InteropGrabBag on
    copying / when object is altered
    

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14. 14 / 15
    FOSDEM 2014 | Miklos Vajna
    Just for Writer?
    ● The API is generic to be used in Calc,
    Impress, etc.
    ● Currently mostly implemented for Writer
    only
    ● Just for OOXML?
    ● It's the only user ATM
    ● Different properties can happy co­exist
    – Most of current keys are prefixed with OOX anyway
    

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15. 15 / 15
    FOSDEM 2014 | Miklos Vajna
    Conclusions
    ● The end result: much improved OOXML
    roundtrip
    ● Now perfect roundtrip examples
    (incomplete list):
    ● Document themes
    ● SmartArt
    ● Table styles
    

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