bug#23806: 24.5; can not set line height

[Eli Zaretskii <eliz@gnu.org>]

tags 23806 + notabug
thanks

> From: ynyaaa@gmail.com
> Date: Mon, 20 Jun 2016 11:15:11 +0900
> 
> `line-height' property is effective only at the newlines,
> so there are no chances to set line height
>   (1) when the line is wrapped
>   (2) when the line is truncated
>   (3) when the line is at the bottom of a buffer
>         and not terminated by newline

Yes.  As clearly documented in the ELisp manual:

     A newline can have a ‘line-height’ text or overlay property that
  controls the total height of the display line ending in that newline.

It talks about "display lines", not physical lines.

The line-height property you put on a newline is designed and
implemented to cater to a specific use case: to allow control of the
effect the newline itself has on the line height.  Since the newline
only affects the height of the display line that ends in that newline,
this is what this feature supports.  It is not a general-purpose way
of controlling the vertical spacing of lines on display.

The node "Line Height" in the ELisp manual describes the line-spacing
variable and frame parameter, which are more general-purpose ways of
controlling vertical layout of text.