Re: Feature proposal/request: Indentation driven by display engine

[Stefan Monnier]

>> Can't you remove the display property when you fold to avoid the problem?
> I could, but then I would have to add and remove text properties during
> each fold/unfold, quite some unnecessary overhead.

Not sure how much of an overhead that would be.  Doesn't seem major.
It might be inconvenient to code, tho.  Is that what you meant?

>>> It then occurred to me that it might be useful to support
>>> such a feature directly in the display engine.
>>> For example, if the line contains text with an `indentation'
>>> property, the display engine would add this amount of white
>>> space to before the beginning of the line, maybe also a vertical
>>> line indicating the location of the margin.
>> 
>> This property would still need to be added to every line.  So basically
>> all you're asking is a "before-string" text-property, maybe?

> Hmm, nice translation of my request.  Yes, basically what I am
> asking for is a working before-string text property.  I know
> that adding the property sounds like a lot of effort, but I could
> use the font-lock/jit-lock setup to get this done efficiently,
> only for the pieces that actually get displayed.

The same has been requested for display properties (e.g. to put
something in the margin without hiding any of the current text, you
need an overlay).

A `before-string' text-property might be doable, but I couldn't tell you
how easy it'd be to add.  If someone wants to implement that, I might
accept it (e.g., as a form of `display' property), but if I were you
I wouldn't hold my breath (we have enough bugs to fix and are getting
close to feature freeze).

The best I can offer for now, is to use overlays which you add via
jit-lock and which you eagerly remove in the background (so they don't
accumulate).

>> How 'bout modifying the actual buffer text directly?

> Yes, this is in fact what I am doing now, I use TAB, and
> wrapping/paragraph-fill support to get fill prefixes.  I also modify
> indentation during promotion and demotion of entries.

> However, there are some disadvantages to this.  One obvious one is
> this:  Org contains a publishing part, and for publishing
> we allow examples like code snippets, where indentation might be
> important.  So the

> #+BEGIN_EXAMPLE

> #+END_EXAMPLE

> construct should be flush to the left margin.

I'm not sure I understand why that makes any difference.

> Are we going to get a before-string property?  WOuld be cool.

Well... patches welcome,


        Stefan