9a5df2f0db
Relaxed atomics really benefit from volatile access since otherwise
the compiler can hoist loads / stores out of loops. For example, in
the typical spin scenario:
while (!_cairo_atomic_int_get_relaxed (&done));
The optimizer can do:
val = _cairo_atomic_int_get_relaxed (&done);
if (!val) {
for (;;);
}
Unless told otherwise, e.g. with volatile or _Atomic, the optimizer
assumes that variables are only accessed by a single thread of execution.
That's also why data races are undefined behaviour in C11.
For GCC and CLang we use an intermediate volatile cast. This works
because GCC and CLang support the Linux Kernel Memory Model (LKMM) [1],
ensuring that:
1. volatile can be applied to single accesses and not necessarily
to the variable itself
2. volatile accesses are atomic for aligned and machine-word sized
variables
For MSVC we use the newer __iso_volatile intrinsics which are recommended
over volatile accesses [2].
Mutex-based fallbacks must all go under the mutex, even relaxed ones,
so we drop the ATOMIC_OP_NEEDS_MEMORY_BARRIER macro.
References:
1. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0124r6.html
2. https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-c4746
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| .gitlab-ci | ||
| boilerplate | ||
| doc | ||
| meson-cc-tests | ||
| perf | ||
| src | ||
| subprojects | ||
| test | ||
| util | ||
| .gitignore | ||
| .gitlab-ci.yml | ||
| AUTHORS | ||
| BUGS | ||
| CODING_STYLE | ||
| COPYING | ||
| COPYING-LGPL-2.1 | ||
| COPYING-MPL-1.1 | ||
| HACKING | ||
| INSTALL | ||
| meson.build | ||
| meson.options | ||
| NEWS | ||
| README.md | ||
| version.py | ||
Cairo: Multi-platform 2D graphics library
What is cairo
Cairo is a 2D graphics library with support for multiple output devices. Currently supported output targets include the X Window System (via both Xlib and XCB), quartz, win32, and image buffers, as well as PDF, PostScript, and SVG file output.
Cairo is designed to produce consistent output on all output media while taking advantage of display hardware acceleration when available (for example, through the X Render Extension).
The cairo API provides operations similar to the drawing operators of PostScript and PDF. Operations in cairo include stroking and filling cubic Bézier splines, transforming and compositing translucent images, and antialiased text rendering. All drawing operations can be transformed by any affine transformation (scale, rotation, shear, etc.).
Cairo has been designed to let you draw anything you want in a modern 2D graphical user interface. At the same time, the cairo API has been designed to be as fun and easy to learn as possible. If you're not having fun while programming with cairo, then we have failed somewhere---let us know and we'll try to fix it next time around.
Cairo is free software and is available to be redistributed and/or modified under the terms of either the GNU Lesser General Public License (LGPL) version 2.1 or the Mozilla Public License (MPL) version 1.1.
Where to get more information about cairo
The primary source of information about cairo is its website:
The latest versions of cairo can always be found at:
Documentation on using cairo and frequently-asked questions:
Mailing lists for contacting cairo users and developers:
Roadmap and unscheduled things to do, (please feel free to help out):
Dependencies
The set of libraries needed to compile cairo depends on which backends are enabled when cairo is configured. So look at the list below to determine which dependencies are needed for the backends of interest.
For the surface backends, we have both "supported" and "experimental" backends. Further, the supported backends can be divided into the "standard" backends which can be easily built on any platform, and the "platform" backends which depend on some underlying platform-specific system, (such as the X Window System or some other window system).
As an example, for a standard Linux build similar to what's shipped by your distro, (with image, png, pdf, PostScript, svg, and xlib surface backends, and the freetype font backend), the following sample commands will install necessary dependencies:
-
Debian (and similar):
apt-get build-dep cairo
-
Fedora (and similar):
dnf builddep cairo
Technically you probably don't need pixman from the distribution since if you're manually compiling Cairo you probably want an updated pixman as well. However, if you follow the default settings and install pixman to /usr/local, your Cairo build should properly use it in preference to the system pixman.
Supported, "standard" surface backends
image backend (required)
- pixman >= 0.30.0
PNG support (preferred)
PDF backend
PostScript backend
SVG backend
- none
Supported, "platform" surface backends
Xlib backend
xlib-xrender backend
- Xrender >= 0.6
Quartz backend
- macOS >= 10.4 with Xcode >= 2.5
Windows backend
- Microsoft Windows Vista or newer.
XCB backend
Font backends (required)
freetype font backend
- freetype >= 2.1.9
- fontconfig
Quartz-font backend
- MacOS X >= 10.4 with Xcode >= 2.5
Windows GDI font backend
- Microsoft Windows Vista or newer
Windows DirectWrite font backend
- Microsoft Windows 7 or newer
Compiling
See the INSTALL document for build instructions.
Licensing
Cairo is released under the terms of either the GNU Lesser General Public License version 2.1, or the terms of the Mozilla Public License version 1.1.
See the COPYING document for more information.
History
Cairo was originally developed by Carl Worth cworth@cworth.org and Keith Packard keithp@keithp.com. Many thanks are due to Lyle Ramshaw without whose patient help our ignorance would be much more apparent.
Since the original development, many more people have contributed to cairo.
See the AUTHORS document for as complete a list as we've been
able to compile so far.