command: extend osd-overlay command with bounds reporting

This is more or less a minimal hack to make _some_ text measurement
functionality available to scripts. Since libass does not support such a
thing, this simply uses the bounding box of the rendered text.

This is far from ideal. Problems include:
- using a bitmap bounding box
- additional memory waste and/or flushing caches
- dependency on window size
- odd small deviations with different window sizes (run osd-test.lua and
  resize the window after each timer update; the bounding boxes aren't
  adjusted in an overly useful way)
- inability to query the size _after_ actual rendering

But I guess it's a start. Since I'm aware that it's crap, add a threat
to the manpage that this may be changed/removed again. For now, I'm
interested whether anyone will have use for it in its current form, as
it's an often requested feature.

1 files changed, 1 insertions, 0 deletions

diff --git a/DOCS/man/lua.rst b/DOCS/man/lua.rst
index a9fc02ed44..92debe8a75 100644
--- a/DOCS/man/lua.rst
+++ b/DOCS/man/lua.rst
@@ -599,6 +599,7 @@ are useful only in special situations.
     ``update()``
         Commit the OSD overlay to the screen, or in other words, run the
         ``osd-overlay`` command with the current fields of the overlay table.
+        Returns the result of the ``osd-overlay`` command itself.
 
     ``remove()``
         Remove the overlay from the screen. A ``update()`` call will add it