vo_vdpau and vo_gl cache the last subtitle bitmaps uploaded to video
card in case they stay the same over multiple frames. Detecting
whether the bitmaps have changed and should be re-uploaded was
somewhat fragile. Change the VO API to provide a bitmap ID which can
be compared with what the VO has to determine whether a new upload of
the bitmaps is needed.
Conflicts:
libvo/vo_gl.c
Note: the changes for vo_gl.c were not merged. Instead, eosd_packer is
modified to use the new way of detecting EOSD changes. This takes care
of vo_gl, vo_gl3 and vo_direct3d, which all render EOSD. They don't
need to be updated in turn.
The code in eosd_packer.c/.h is taken from vo_vdpau.c and has been made
independent from vdpau API specifics. This allows other VOs, which need
to pack the small EOSD images into a large surface for efficiency, to use
this code.