Re: Question about display engine

[martin rudalics]

> Indeed, nothing is ever as simple in the display code, due to the
> sheer amount of different use cases.  I think at least one other face
> attribute that's special in this regard is :box, in particular (but
> not only) because extend_face_to_end_of_line is called from the
> function which redisplays the mode line and the header line.

Newlines within boxes are a pain.  Ideally, the entire text should be
enclosed within one single box.  Which obviously fails when the text
does not form a rectangular region on screen.  This is also evident
with buttons - you cannot draw a button with multiple lines of text.

As for the mode-/header-line or tooltip faces we'd probably have these
always extend to the end of line, overriding any extension property
specified for the underlying face.  There's also the case of remapped
backgrounds that IIRC cannot extend to the bottom edge of a window -
they stop with the last text line displayed (I have to look into this
matter again to say more).

martin