[RFC PATCH v1] libcamera: controls: Generate macro for each control

[Laurent Pinchart]

On Tue, Mar 18, 2025 at 09:11:27AM +0100, Jacopo Mondi wrote:
> On Mon, Mar 17, 2025 at 10:00:20PM +0100, Barnabás Pőcze wrote:
> > 2025. 03. 17. 19:54 keltezéssel, Jacopo Mondi írta:
> > > On Mon, Mar 17, 2025 at 07:11:46PM +0100, Barnabás Pőcze wrote:
> > > > Generate a macro in the form of LIBCAMERA_HAS_$VENDOR_$MODE_$NAME
> > > > for each control so that its existence can be checked easily
> > > > and without extra version checks.
> > > >
> > > > Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
> > >
> > > Do we really want this ?
> >
> > Good question, hence the RFC; I don't think there is a very nice
> > way to discover (and use) controls at comptime/runtime. Also note
> 
> What would the use case be ?
> 
> > that the control namespaces already have their own existence macros
> > (e.g. `LIBCAMERA_HAS_RPI_VENDOR_CONTROLS`).
> 
> >
> > > Applications should discover controls
> > > programmatically.
> >
> > What do you have in mind? Looking up the numeric id in the appropriate
> > `ControlIdMap` by the (namespace, name) pair?
> 
> If you mean Camera::controls() and Camera::properties() then yes, I
> think applications should enumerate the supported controls from there
> and not rely on compile-time defines, as even if a control is defined
> it doesn't mean it is supported by the camera.

True, but an application that would check if Camera::controls()
contains, for instance, controls::AE_ENABLE with

	if (camera->controls().count(controls::AE_ENABLE))

will not compile if the libcamera version it compiles against does not
define the AeEnable control. Barnabás' patch allows fixing that with
conditional compilation.

> > > Or is this useful for ABI compliance validation ?
> > >
> > > > ---
> > > >   include/libcamera/control_ids.h.in | 1 +
> > > >   1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/include/libcamera/control_ids.h.in b/include/libcamera/control_ids.h.in
> > > > index 5d0594c68..8f037589d 100644
> > > > --- a/include/libcamera/control_ids.h.in
> > > > +++ b/include/libcamera/control_ids.h.in
> > > > @@ -49,6 +49,7 @@ extern const std::array<const ControlValue, {{ctrl.enum_values_count}}> {{ctrl.n
> > > >   extern const std::map<std::string, {{ctrl.type}}> {{ctrl.name}}NameValueMap;
> > > >   {% endif -%}
> > > >   extern const Control<{{ctrl.type}}> {{ctrl.name}};
> > > > +#define LIBCAMERA_HAS_{{vendor|upper}}_{{mode|upper}}_{{ctrl.name|snake_case|upper}}
> > > >   {% endfor -%}
> > > >
> > > >   {% if vendor != 'libcamera' %}

-- 
Regards,

Laurent Pinchart