[FFmpeg-user] drawbox: text subpixel rendering

[Nikita Zlobin]

By some reason text is rendered grayscale, despite horizontal rgb is
default x11 settings, and drawtext uses libfreetype.

Shell command:

stdbuf -o0 yes | SDL_AUDIODRIVER=alsa \
ffplay -v quiet -f rawvideo -pixel_format gray -video_size 1x1 -codec:v
rawvideo -framerate 20000 \ -vf "
    nullsink, nullsrc = 128x32, scale = flags = bicubic, format = gray,
    drawtext = text=Example : x=3 : y=3 : font=serif : fontsize=14 :
fontcolor=white " -

Result: https://imgur.com/JAHZ6Wh.png

ffmpeg version: from gentoo portage, 4.4.1-r2

If it's misconfiguration - would be great to know, how to configure.
Also, if it's fixed in upstream.