[libcamera-devel] [RFC PATCH 0/5] Libcamera Controls

[Kieran Bingham]

I've been sketching out these controls for a bit, and I wanted to get them on
the list as a refernce point for some furthur discussions.

The patches are based on top of a combination of both Jacopo's V4L2 Control
series, and Niklas' enum series.

I am still undecided as to whether the best route forwards is to keep the
controls as a std::set <Control> with the Control class handling the ID and
type checking, or if a std::map<ControlID, ControlValue> might be more
flexible.

With a control class, I can make sure the construction logic is contained, but
I lose the ease of 'mapping' an ID to the control value within the std::set.
I've implemented a comparator, which allows the use of .find(), but I'm not
sure I'm fond of that yet, especially in the pain points of handling searching
for an ID which isn't in the set.

I'd love to be able to make a set operate more like a map using the internal
key, or perhaps make a map look more like a set, so that the ID and Value are
more closely associated.


I have also considered that I could update Jacopo's V4L2 controls to utilise
the ControlValue type, which would then allow for any controls which want to
map directly to a V4L2 control - the ControlValue itself could be passed to the
V4L2 layer and populated there. However this would only then push the
requirement to 'find' the appropriate ControlValue object down to the V4L2
layer.

Anyway, there's a lovely demo at the end which shows setting the Brightness
control from the qcam application as a sine wave which makes for a visual
clarification that the controls are successfully being set.

As noted there, We will likely want to extend controls such that a particular
control knows about it's max/min/default values. And that then (to me) provides
another argument to use the class Control with a set over a map.

Anyway, any thoughts on a postcard sized reply. Please don't focus on typos' or
grammar, as this is an RFC about the usage and API more than the patches
themselves.


Kieran Bingham (5):
  libcamera: Add control handling
  libcamera: request: add a control set
  libcamera: pipeline: Add readControls(), writeControl() interfaces
  QCam: Set a read control on each request to get Gain value
  [PoC] QCam: Control demo: A SineWave Brightness

 include/libcamera/controls.h             | 106 ++++++++
 include/libcamera/meson.build            |   1 +
 include/libcamera/request.h              |   4 +
 src/libcamera/controls.cpp               | 310 +++++++++++++++++++++++
 src/libcamera/include/pipeline_handler.h |   3 +
 src/libcamera/meson.build                |   1 +
 src/libcamera/pipeline/ipu3/ipu3.cpp     |  19 ++
 src/libcamera/pipeline/raspberrypi.cpp   | 108 +++++++-
 src/libcamera/pipeline/rkisp1/rkisp1.cpp |  19 ++
 src/libcamera/pipeline/uvcvideo.cpp      | 127 +++++++++-
 src/libcamera/pipeline/vimc.cpp          |  19 ++
 src/qcam/main_window.cpp                 |  24 ++
 12 files changed, 739 insertions(+), 2 deletions(-)
 create mode 100644 include/libcamera/controls.h
 create mode 100644 src/libcamera/controls.cpp

-- 
2.20.1