draw line

[Jonas Bernoulli]

I would like to draw a one-pixel line. I have tried quite a few things
by now but none of them works.

Here are two ways I have tried. Evaluating them should draw a red line
on the next line, which is only one pixel high.

(insert (concat "\n" (propertize "\n" 'face '(:background "red")
'display '(space :height (1)))))

(insert (concat "\n" (propertize "\n" 'face '(:background "red")
'line-height 1)))

This doesn't sound very promissing:

38.11 Line Height
... However, no matter what you specify, the actual line height can
never be less than the default. ...

But I know that some time ago I managed to draw a one-pixel line. I
just don't remember how I did it. So I don't know if I just can't come
up with the proper way of doing it anymore or if this is just not
possible anymore in 23.0. I have tried the expressions above with 22.1
without success also. But I don't know if I used 21 or 22 back when I
managed to draw a one-pixel line.

Anyways, does anyone know of a way to draw a line?

-- Jonas