Re: CSS support in libsvgtiny

On 14/09/2023 14:43, Michael Drake wrote:
> Hi Michael,
>
> On Tue, 12 Sept 2023 at 23:45, Michael Orlitzky <michael@orlitzky.com> wrote:
>
>> I dumped the new properties into the default level, but this raises
>> a question: should libcss use a different CSS level for SVG?
>
> Good question. What do you think John-Mark?

I'm not sure it's necessary -- libcss will simply expose any and all
properties it knows about (and apply the cascade as appropriate).
However, it is not responsible for applying the resulting computed
styles to the document -- that is up to the client. A non-SVG-aware
client would never look at them and thus would be none the wiser as to
their existence. Obviously an SVG-aware client would look at them.

The only potentially difficult case would be an SVG-aware client that is
applying CSS to something that isn't an SVG. However, the client itself
would have to deal with that by ensuring it ignored these properties
when the document it's dealing with is not an SVG.

>>
>> 3. I copied the css_select_handler and css_unit_ctx from netsurf into
>> svgtiny.c. Thankfully, I didn't have to think about the unit
>> conversions at all because opacity is a float. The select handler
>> callbacks were tedious, but most of them can be copied from netsurf
>> with minimal changes, fudging interned string names and replacing
>> html-only function calls. I wound up copying the user data handler
>> too. Who knows if any of this stuff works, but it hasn't crashed.
>>
>> Ultimately, since netsurf uses libsvgtiny, copy-pasting the select
>> handler wouldn't be a great solution. I think it would make sense
>> to factor out the libdom/libcss integration into something like a
>> libdom-css that provides a generic css_select_handler
>> implementation.
>
> I agree, it would be better to have a shared implementation of the
> LibCSS/LibDOM integration. Either as a LibDOM-CSS or maybe as
> an optional LibDOM binding for LibCSS, a bit like LibDOM has
> the Hubbub/LibXML bindings. What do you think John-Mark?

I have no strong view, other than to observe that the code in NetSurf
itself is licensed under GPLv2, and not MIT/Expat (as used by most of
the libraries), so simply copying it probably isn't the right answer. I
don't recall who has contributed to that code, but any relicensing
thereof would need their permission.

Note also that, as with the SVG-specific properties, the expectation was
always that various parts of the selection handler would have to be
document-format aware (e.g. extracting the presentational hints from an
HTML document is not something that would be wanted when processing some
other document format).


John-Mark.
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