Hi Laurent, Mauro,
We currently have two competing utilities for controlling media devices:
media-ctl and mc_nextgen_test, each with features that the other doesn't
have. That's obviously not good.
I would like to work on adding the missing pieces for the new G_TOPOLOGY
API to media-ctl. As part of that I would really like to turn media-ctl
into C++ (like the other V4L2/CEC utilities) so I can use the v4l2-info.cpp
and media-info.cpp helpers. This will ensure consistent naming conventions
throughout our utilities, which I think is a good thing. With C++ you can
also use the standard STL maps, lists, vectors, etc. which are ideal for
processing a media topology.
One thing that I really dislike about the media-ctl syntax is the use of
characters that require quotes ('->' being the main offender). I would like
to add an alternative syntax that avoids this.
I'm thinking that ' to ' (note the spaces) is a good alternative to '->'.
Question: does '->' already require spaces? Or is 'pad1->pad2' equivalent
to 'pad1 -> pad2'? I haven't dug into the parsing code yet.
I'm a bit confused by this syntax:
entity = entity-number | ( '"' entity-name '"' ) ;
Shouldn't this be:
entity = entity-number | entity-name ;
The first syntax suggests that all entity-names must be written as "name",
and that can't be right. Just checking if the entity string starts with
0-9 is enough. If you want to allow entity names to start with 0-9 as
well (a bad idea IMHO), then you can be fancier and check if the entity
string matches either [0-9]+ or 0[xX][0-9]+.
Assuming that brackets around the entity name are indeed not needed, then
the only other annoying syntax is for rectangles: (left,top)/wxh.
The () also need to be quoted. I was wondering if the () around left,top are
needed at all. Wouldn't left,top/WxH be sufficient? Rectangles are prefixed by
crop: or compose:, so it's easy to know when you have to parse a rectangle.
I think that with these changes in place you can setup pipelines without
having to care about escaping or quoting special characters.
My plan is to first convert media-ctl to C++ (with minimum changes) and
start using v4l2-info.cpp and media-info.cpp to ensure consistent naming.
The next step is to support an easier alternative syntax, and finally
G_TOPOLOGY support will be added to media-ctl so it has the same feature
set as mc_nextgen_test.
Hopefully by the time that's done we'll also have properties, so that will
be added as well.
I am uncertain what to do with libmediactl.c. It is only used by media-ctl,
and it is never installed either. I am inclined to first make something
that works, and then think about creating a proper library. Splitting off
the parsing in a separate source is a good idea regardless, so I was
planning to do that anyway.
Any objections? Ideas? Comments?
Regards,
Hans
