299e8ef563
A range-based for loop whose range expression is an array of char
pointers and range variable declaration is a const reference to a
std::string creates a temporary string from the char pointer and binds
the range variable reference to it. This creates a const reference to a
temporary, which is valid in C++, and extends the lifetime of the
temporary to the lifetime of the reference.
However, lifetime extension in range-based for loops is considered as a
sign of a potential issue, as a temporary is created for every
iteration, which can be costly, and the usage of a reference in the
range declaration doesn't make it obvious that the code isn't simply
binding a reference to an existing object. gcc 11, with the
-Wrange-loop-construct option, flags this:
uvcvideo.cpp:432:33: error: loop variable 'name' of type 'const string&' {aka 'const std::__cxx11::basic_string<cha
r>&'} binds to a temporary constructed from type 'const char* const' [-Werror=range-loop-construct]
| 432 | for (const std::string &name : { "idVendor", "idProduct" }) {
| | ^~~~
To please the compiler, make the range variable a const char *. This may
bring a tiny performance improvement, as the name is only used once, in
a location where the compiler can use
operator+(const std::string &, const char *)
instead of
operator+(const std::string &, const std::string &)
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Use a const char * type instead of auto, and update the commit message
accordingly.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
.. 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 (>= 0.55) 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 python3-ply python3-jinja2
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 cam: [optional]
libevent-dev
for qcam: [optional]
qtbase5-dev libqt5core5a libqt5gui5 libqt5widgets5 qttools5-dev-tools libtiff-dev
for tracing with lttng: [optional]
liblttng-ust-dev python3-jinja2 lttng-tools
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 a 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