[vlc-devel] [PATCH] dvbsub.c : Don't fill region if page_state == 0

simon h btsimonh at googlemail.com
Fri Jun 18 23:13:43 CEST 2010

Björn wrote:

> You can look at region_fill_flag as either a function call or a style indicator. If you see it as a function call, the> decoder should fill the region every time it sees the flag. However, paragraph "5.3.4 Region fill" says:
>  Where the region fill flag is set, the region fill in the subtitle decoder

>  model happens before any objects are rendered into the region.
> This suggests that the decoder should not fill a region after it has had objects rendered onto it. Alternatively, that> if you refill the region you must re-render the objects.

> And this fits rather well with viewing the flag as a style indicator instead, meaning "this region should have a fille> d background." Any subsequent "normal case" packets hence naturally have the flag set too, since the style has not cha> nged.

from 5.1.5 Region composition:
"The value of the
region_n-bit_pixel_code shall not change in RCS where the region_fill_flag
is not set. This allows decoders that have
already acquired the subtitling service to ignore the
region_n-bit_pixel_code when the region_fill_flag is not set. A
decoder in the process of acquiring the service can rely on the
region_n-bit_pixel_code being the current region fill
colour regardless of the state of region_fill_flag."

This indicates that the fill flag is designed to be set once to cause a
fill, and then cleared.  If a decoder acquires the service and a region is
'new' to the decoder, it should fill with the existing colour.  This
indicates that a regions is ALWAYS filled when first encountered (used,
actually) (i.e. if you want it transparent, set a transparent colour...),
and the fill flag is used to indicate the packet in which it is wished for
this to occur.  All regions have a 'style' of 'filled' :)
Since regions can be removed from display, filled, and then re-revealed,
then the ability to clear them on demand is essential.
'5.4.3 Region Fill' also states:
"Setting the region fill flag instructs that the region is to be completely
re-drawn with the defined fill colour."
Again, this indicates the 'command' interpretation rather than the 'style
indicator' interpretation.

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