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API improvements in LibreOffice

Estimated read time: 3 minutes

I worked on two small features to extend the public (UNO) API of LibreOffice. First, thanks to Vector for funding Collabora to make this possible.

Aliased paths and text in the PNG export for Draw

The UNO API of Draw allows you to build quite complex and custom shapes, but you may want to export the rendered result to a bitmap for testing purposes, so you can assert that the actual result matches a reference one.

One problem in this area is anti-aliasing, which can easily differ between machines. Given that normally aliased rendering is ugly, there is now a way to enable AA, but disable it just during a single invocation of the PNG exporter.

The above picture shows how the AA result looks like. You could write a Basic macro like this to trigger the PNG export from Draw:

xExporter = createUnoService("")
Dim aArgs(1) As new
aArgs(0).Name  = "URL"
aArgs(0).Value = "file:///tmp/debug/aa.png"
aArgs(1).Name  = "MediaType"
aArgs(1).Value = "image/png"

Let’s see how it looks like if you turn AA off:

You just need to specify a new Antialiasing key under FilterData:

Dim aFilterData(0) As new
aFilterData(0).Name = "AntiAliasing"
aFilterData(0).Value = False
xExporter = createUnoService("")
Dim aArgs(2) As new
aArgs(0).Name  = "URL"
aArgs(0).Value = "file:///tmp/debug/non-aa.png"
aArgs(1).Name  = "FilterData"
aArgs(1).Value = aFilterData()
aArgs(2).Name  = "MediaType"
aArgs(2).Value = "image/png"

You can imagine which rendering result is easier to debug when the reference and the actual bitmap doesn’t match. ;-)

This feature is available for other bitmap formats as well, PNG is only an example.

Default character style in Writer

In most cases you don’t really need a default character style: if you’re fine with a default, then the default paragraph style should be enough for your needs. In general, paragraph styles can contain character properties, so if the default is fine for you, you just don’t set a character style.

However, there is an exception to all rules. If you want to reset the current character style, it makes sense to just set the CharStyleName property to a default value, especially since this works with paragraph styles already.

Now you can write C++ code like this (see SwUnoWriter::testDefaultCharStyle() for a full example):

xCursorProps->setPropertyValue("CharStyleName", uno::makeAny(OUString("Standard")));

And it’ll be handled as Default Style in English builds, or their localized versions in a non-English UI.

All this is available in master (towards LibreOffice 6.2), or you can grab a daily build and try it out right now. :-)

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