Commit 287a0b4 introduced a segfault when validating the i3 config
as the root_screen will not be set in this case, causing a null
pointer dereference.
fixes#2144
Re-introduce fully-fledged get_colorpixel function, which enables arbitrary
color depths for the display. The previous code is kept as an optimization for
the case of a true color display, where a X11 roundtrip is unnecessary.
We pass alpha channel information to the current text drawing code
and use it if it is available. The previous behavior of using full
opacity for RGB format colors is preserved.
You need to specify the --enable-32bit-visual flag when starting i3. This is
done because everything feels sluggish on my system when using a 32 bit visual
instead of a 24 bit visual. Fast > fancy.
