libvo --- the library to handle video output    by A'rpi, 2002.04
============================================

Note: before start on this, read colorspaces.txt !

The constants for different pixelformats are defined in img_format.h,
their usage is mandatory.

WARNING: Please keep in mind that some of this information may be out-dated,
so if you are working on a new vo, consider submitting preliminary patches
very early on. Currently vo_gl is one of the more up-to-date VOs to use
as reference if you are unsure about something and do not want to ask on the
list.
vo_vdpau and vo_direct3d may be a good choice, too, they use different
approaches closer to the sometimes convoluted way DirectX works.

Each vo driver _has_ to implement these:

   preinit():
       init the video system (to support querying for supported formats)

   uninit():
     Uninit the whole system, this is on the same "level" as preinit.

   control():
     Current controls (VOCTRL_QUERY_FORMAT must be implemented,
     VOCTRL_DRAW_IMAGE, VOCTRL_FULLSCREEN, VOCTRL_UPDATE_SCREENINFO
     should be implemented):
        VOCTRL_QUERY_FORMAT  -  queries if a given pixelformat is supported.
               It also returns various flags decsirbing the capabilities
               of the driver with teh given mode. for the flags, see
               file vfcaps.h !
               the most important flags, every driver must properly report
               these:
                   0x1  -  supported (with or without conversion)
                   0x2  -  supported without conversion (define 0x1 too!)
                   0x100  -  driver/hardware handles timing (blocking)
               also SET sw/hw scaling and osd support flags, and flip,
               and accept_stride if you implement VOCTRL_DRAW_IMAGE (see bellow)
               NOTE: VOCTRL_QUERY_FORMAT may be called _before_ first config()
               but is always called between preinit() and uninit()
        VOCTRL_GET_IMAGE
               libmpcodecs Direct Rendering interface
               You need to update mpi (mp_image.h) structure, for example,
               look at vo_x11, vo_sdl, vo_xv or mga_common.
        VOCTRL_DRAW_IMAGE
               replacement for the current draw_slice/draw_frame way of
               passing video frames. by implementing SET_IMAGE, you'll get
               image in mp_image struct instead of by calling draw_*.
               unless you return VO_TRUE for VOCTRL_DRAW_IMAGE call, the
               old-style draw_* functils will be called!
               Note: draw_slice is still mandatory, for per-slice rendering!
        VOCTRL_RESET  -  reset the video device
               This is sent on seeking and similar and is useful if you are
               using a device which prebuffers frames that need to flush them
               before refilling audio/video buffers.
        VOCTRL_PAUSE
        VOCTRL_RESUME
        VOCTRL_GUISUPPORT
               return true only if driver supports co-operation with
               MPlayer's GUI (not yet used by GUI)
        VOCTRL_SET_EQUALIZER
               set the video equalizer to the given values
               two arguments are provided: item and value
               item is a string, the possible values are (currently):
                   brightness, contrast, saturation, hue
        VOCTRL_GET_EQUALIZER
               get the current video equalizer values
               two arguments are provided: item and value
               item is a string, the possible values are (currently):
                   brightness, contrast, saturation, hue
        VOCTRL_ONTOP
               Makes the player window stay-on-top. Only supported (currently)
               by drivers which use X11, except SDL, as well as directx and
               gl2 under Windows.
        VOCTRL_BORDER
               Makes the player window borderless.
        VOCTRL_FULLSCREEN
               Switch from and to fullscreen mode
        VOCTRL_GET_PANSCAN
        VOCTRL_SET_PANSCAN
               Needed to implement pan-scan support ('w' and 'e' keys during
               playback in fullscreen mode)
        VOCTRL_START_SLICE
               Called before the first draw_slice of each frame, useful if
               you need to do some set-up work.
        VOCTRL_DRAW_EOSD
               Required for EOSD (ASS subtitle) support. Provides all
               information necessary to draw the EOSD for the current video
               frame.
        VOCTRL_GET_EOSD_RES
               Required for EOSD (ASS subtitle) support. Informs the ASS
               renderer about the properties of the drawing area (size,
               borders).
        VOCTRL_SET_DEINTERLACE
        VOCTRL_GET_DEINTERLACE
               Get or set deinterlacing status for VOs that support some kind
               of deinterlacing.
        VOCTRL_UPDATE_SCREENINFO
               Should set the xinerama_x, xinerama_y, vo_screenwidth and
               vo_screenheight appropriately for the currently used
               monitor and -xineramascreen option.
               Usually should simply call the w32_update_xinerama_info or
               update_xinerama_info function.
               By supporting this, the VO also requests the newer API
               that sets vo_dx, vo_dy etc. appropriately before config()
               is called.

   config():
     Set up the video system. You get the dimensions and flags.
     width, height: size of the source image
     d_width, d_height: wanted scaled/display size (it's a hint)
     Flags:
       0x01    - force fullscreen (-fs)
       0x02    - allow mode switching (-vm)
       0x04    - allow software scaling (-zoom)
       0x08    - flipping (-flip)
     They're defined as VOFLAG_* (see libvo/video_out.h)

     IMPORTANT NOTE: config() may be called 0 (zero), 1 or more (2,3...)
     times between preinit() and uninit() calls. You MUST handle it, and
     you shouldn't crash at second config() call or at uninit() without
     any config() call! To make your life easier, vo_config_count is
     set to the number of previous config() call, counted from preinit().
     It's set by the caller (vf_vo.c), you don't have to increase it!
     So, you can check for vo_config_count>0 in uninit() when freeing
     resources allocated in config() to avoid crash!

     You should implement VOCTRL_UPDATE_SCREENINFO so that vo_dx, vo_dy,
     vo_dwidth and vo_dheight are already pre-set to values that take
     aspect and -geometry into account. It is also necessary to properly
     support multi-monitor setups (if based on x11_common, w32_common).

   draw_slice(): this displays YV12 pictures (3 planes, one full sized that
        contains brightness (Y), and 2 quarter-sized which the colour-info
        (U,V). MPEG codecs (libmpeg2, opendivx) use this. This doesn't have
        to display the whole frame, only update small parts of it.
        If this is not supported, it must be signaled in QUERY_FORMAT with
        VOCAP_NOSLICES.

   draw_frame(): this is the older interface, this displays only complete
        frames, and can do only packed format (YUY2, RGB/BGR).
        Win32 codecs use this (DivX, Indeo, etc).
        If you implement VOCTRL_DRAW_IMAGE, you do not need to implement draw_frame.

   draw_osd(): this displays subtitles and OSD.
        It's a bit tricky to use it, since it's a callback-style stuff.
        It should call vo_draw_text() with screen dimension and your
        draw_alpha implementation for the pixelformat (function pointer).
        The vo_draw_text() checks the characters to draw, and calls
        draw_alpha() for each. As a help, osd.c contains draw_alpha for
        each pixelformats, use this if possible!
        Note that if you do not draw directly onto the video you should
        use vo_draw_text_ext() which allows you to specify the border
        values etc. needed to draw DVD menu highlights at the correct place.
        If you do not want to implement this, you can still use -vf
        expand=osd=1 to draw the OSD, or even implement code to insert
        this filter automatically.
        Make sure you set VFCAP_OSD depending on whether you implemented it
        or not.

        NOTE: This one will be obsolete soon! But it's still useful when
        you want to do tricks, like rendering osd _after_ hardware scaling
        (tdfxfb) or render subtitles under of the image (vo_mpegpes, sdl)

        NOTE2: above NOTE is probably wrong, there are currently no plans to
        obsolete draw_osd, though there is the more advanced EOSD support for
        ASS subtitles.

   flip_page(): this is called after each frame, this displays the buffer for
        real. This is 'swapbuffers' when doublebuffering.
        Try to do as little work here as possible, since that affect jitter/
        A-V sync.

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