bug#21835: 25.0.50; cursor height wrong when line-spacing is used

[Eli Zaretskii]

> From: David Reitter <david.reitter@gmail.com>
> Date: Thu, 5 Nov 2015 22:12:03 -0500
> Cc: 21835@debbugs.gnu.org
> 
> One could default to the height of the last glyph of the line. Normally, we 
> would expect the size of the cursor to indicate the general height of the 
> text that would be inserted there, and the last glyph is the best guess.

I tried that, and it was worse.  The problem is, the last glyph could
have very small height, at least with some fonts.  Then you have a
very small cursor at the end.  What's more, as you type at EOL, the
cursor height will constantly change.

> Alternatively, use the line height for all cursor positions in that line.  In 
> that case, things would still need to be adjusted for `line-spacing’, and 
> based on what you wrote, I think that’s less preferable.

Indeed.  Our cursor, when it is drawn on a character, shows the
dimensions of that character, both horizontal and vertical.  Losing
that, even only for the vertical dimension, would be a step backward,
I think.

There are also differences in how we draw the hollow cursor (in
non-selected windows) vs the cursor in selected windows.  They should
have the same dimensions, or else it will look like a bug.  The
solution I coded solves this problem as well (some other ideas
didn't).

So once again, I don't know of any better way of solving this.