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Laurent Pinchart 581bb27495 libcamera: controls: Disable ControlValue<T> construction from unsupported T
The ControlValue<T> constructor for non-array values is a template
function that participates in overload resolution for all T types that
are not Span or std::string. Other T types that are not supported then
result in a compilation error.

This causes issues when calling an overloaded function that can accept
both a ControlValue and a Span with an std::array<U> parameter. The
first overload will be resolved using implicit construction of a
ControlValue from the std::array<U>, while the second overload will be
resolved using implicit construction of a Span<U> from the
std::array<U>. This results in a compilation error due to an ambiguous
function call.

The first overload is invalid, selecting it would result in a
compilation error in the ControlValue constructor, as the
ControlValue<T> constructor doesn't support std::array<U> for type T.
The compiler can't know about that, as overload resolution happens
earlier.

To fix it, we can disable the ControlValue<T> constructor for
unsupported types T, moving the type check from compilation of the
function to overload resolution. The constructor will not participate in
overload resolution, and the call won't be ambiguous. The end result is
the same for unsupported types, compilation will fail.

Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
2020-10-26 17:51:32 +01:00
.reuse qcam: Specify Feather icons license in DEP5 2020-06-09 23:26:13 +03:00
Documentation libcamera: Omit extra semicolons 2020-10-20 13:15:52 +03:00
include libcamera: controls: Disable ControlValue<T> construction from unsupported T 2020-10-26 17:51:32 +01:00
LICENSES licenses: License all meson files under CC0-1.0 2020-05-13 16:46:24 +03:00
package/gentoo/media-libs/libcamera licenses: Add SPDX headers to Gentoo ebuild 2020-04-15 19:51:56 +03:00
src android: jpeg: encoder: Use pass-by-value for Exif parameter 2020-10-23 22:53:17 +03:00
test libcamera: Drop unneeded empty default constructors and destructors 2020-10-23 22:48:17 +03:00
utils utils: hooks: pre-push: Accept Acked-by in addition to Reviewed-by 2020-10-02 15:30:14 +03:00
.clang-format licenses: Replace deprecated GPL-2.0 with GPL-2.0-only 2020-04-15 19:51:56 +03:00
.gitignore libcamera: Add missing SPDX headers to miscellaneous small files 2020-06-09 23:26:13 +03:00
COPYING.rst libcamera: Summarize licensing terms in COPYING.rst 2020-06-26 15:18:25 +03:00
meson.build meson: Enable shadowed variable warning 2020-10-21 17:18:49 +01:00
meson_options.txt Documentation: Move all dependencies into features 2020-09-24 21:08:30 +03:00
README.rst meson: Bump meson version to 0.51 2020-09-24 21:08:34 +03:00

.. SPDX-License-Identifier: CC-BY-SA-4.0

.. section-begin-libcamera

===========
 libcamera
===========

**A complex camera support library for Linux, Android, and ChromeOS**

Cameras are complex devices that need heavy hardware image processing
operations. Control of the processing is based on advanced algorithms that must
run on a programmable processor. This has traditionally been implemented in a
dedicated MCU in the camera, but in embedded devices algorithms have been moved
to the main CPU to save cost. Blurring the boundary between camera devices and
Linux often left the user with no other option than a vendor-specific
closed-source solution.

To address this problem the Linux media community has very recently started
collaboration with the industry to develop a camera stack that will be
open-source-friendly while still protecting vendor core IP. libcamera was born
out of that collaboration and will offer modern camera support to Linux-based
systems, including traditional Linux distributions, ChromeOS and Android.

.. section-end-libcamera
.. section-begin-getting-started

Getting Started
---------------

To fetch the sources, build and install:

::

  git clone git://linuxtv.org/libcamera.git
  cd libcamera
  meson build
  ninja -C build install

Dependencies
~~~~~~~~~~~~

The following Debian/Ubuntu packages are required for building libcamera.
Other distributions may have differing package names:

A C++ toolchain: [required]
	Either {g++, clang}

Meson Build system: [required]
        meson (>= 0.51) ninja-build pkg-config

        If your distribution doesn't provide a recent enough version of meson,
        you can install or upgrade it using pip3.

        .. code::

            pip3 install --user meson
            pip3 install --user --upgrade meson

for the libcamera core: [required]
        python3-yaml

for IPA module signing: [required]
        libgnutls28-dev openssl

for the Raspberry Pi IPA: [optional]
        libboost-dev

        Support for Raspberry Pi can be disabled through the meson
         'pipelines' option to avoid this dependency.

for device hotplug enumeration: [optional]
	libudev-dev

for documentation: [optional]
	python3-sphinx doxygen graphviz

for gstreamer: [optional]
	libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev

for qcam: [optional]
	qtbase5-dev libqt5core5a libqt5gui5 libqt5widgets5 qttools5-dev-tools libtiff-dev

Using GStreamer plugin
~~~~~~~~~~~~~~~~~~~~~~

To use GStreamer plugin from source tree, set the following environment so that
GStreamer can find it.

  export GST_PLUGIN_PATH=$(pwd)/build/src/gstreamer

The debugging tool `gst-launch-1.0` can be used to construct and pipeline and test
it. The following pipeline will stream from the camera named "Camera 1" onto the
default video display element on your system.

.. code::

  gst-launch-1.0 libcamerasrc camera-name="Camera 1" ! videoconvert ! autovideosink

.. section-end-getting-started