Re: Layered display API

[Bo Lin <bo@dreamsphere.org>]

Hi,

Eli Zaretskii <eliz@gnu.org> writes:

>> > What I meant is this: if you need to display below the last line of
>> > the buffer text, put the overlay at EOB, and include newlines in the
>> > overlay string when you need to move to the next screen line.  To
>> > align text horizontally you could use spaces or align-to display
>> > properties in the string.
>> 
>> Yes, I might try this, as soon as there's some suggestion how to handle 
>> the problem of `line-prefix' in this multi-overlay approach.
>
> Find the longest prefix and align everything so that the left edge
> keeps clear of that?

Zero length overlays don't get displayed so this won't work when the
buffer is empty. Not a game breaker of course, but for a completion
tooltip it's still an undesirable defect.

>> >>      This is indeed a missing feature.  It should be easy enough to provide
>> >>      some special kind of display property that would overlay any other
>> >>      displayed content
>> >>
>> >>
>> >> That would leave a question where will it have to be set on.
>> >> Would that new kind of overlay be able to be displayed far
>> >> from the position it's set on?
>> >
>> > No, I meant conceal the text produced by other display properties, and
>> > display your overlay string instead.
>> 
>> It doesn't seem to be solving much: if I want to display something in 
>> the middle of, say, large `display' text, there's no specific span of 
>> text to set that new property on.
>
> You'd put it on the overlay string.

Ideally, for a popup tooltip, it should cover only the small
rectangular area that is the tooltip, while leaving everything else
intact to minimize visual disturbances. This is, AFAICT, currently
impossible to achieve if you have to conceal anything with a
'display property, because: 1) in the simplest case the 'display is
a string, but you don't know the proper display width of each
character; and 2) the 'display can be not-strings.

-Bo