
The old calculation was introduced to improve the precision with commit c16a5ec1cf14d67ee8100afd31a2e85e7003f9a8. Here, I call the calculation as "revision 2", and the calculation even older as "revision 1", and the new calculation introduced with this commit as "reivion 3". Revision 2 has two problems: 1. The calculation is mixed with fixed-point numbers and floating-point numbers. To overcome the precision loss of fixed-point numbers division, it first "calculates refresh rate in milliHz first for extra precision", but this requires converting the value back to Hz. An extra calculation has performance and precision costs. It is also hard to understand for programmers. 2. The calculation has a bias. In the process, it does: refresh += (drm_mode->vtotal / 2); It prevents the value from being rounded to a smaller value in a fixed-point integer arithmetics, but it only adds a small bias (0.0005) and consumes some fraction bits for floating point arithmetic. Revision 3, introduced with this commit always uses double-precision floating-point values for true precision and to ease understanding of this code. It also removes the bias. Another change is that it now has two internal values, numerator and denominator. Revision 1 also calculated those two values first, and later performed a division with them, which minimizes the precision loss caused by divisions. This method has risks of overflowing the two values and revision 1 caused problems due to that, but revision 3 won't thanks to double-precision. Therefore, revision 3 will theoretically have the result identical with the calculation with infinite-precision. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1737>
Mutter
Mutter is a Wayland display server and X11 window manager and compositor library.
When used as a Wayland display server, it runs on top of KMS and libinput. It implements the compositor side of the Wayland core protocol as well as various protocol extensions. It also has functionality related to running X11 applications using Xwayland.
When used on top of Xorg it acts as a X11 window manager and compositing manager.
It contains functionality related to, among other things, window management, window compositing, focus tracking, workspace management, keybindings and monitor configuration.
Internally it uses a fork of Cogl, a hardware acceleration abstraction library used to simplify usage of OpenGL pipelines, as well as a fork af Clutter, a scene graph and user interface toolkit.
Mutter is used by, for example, GNOME Shell, the GNOME core user interface, and by Gala, elementary OS's window manager. It can also be run standalone, using the command "mutter", but just running plain mutter is only intended for debugging purposes.
Contributing
To contribute, open merge requests at https://gitlab.gnome.org/GNOME/mutter.
It can be useful to look at the documentation available at the Wiki.
Coding style and conventions
The coding style used is primarily the GNU flavor of the GNOME coding style with some additions:
-
Use regular C types and
stdint.h
types instead of GLib fundamental types, except forgboolean
, andguint
/gulong
for GSource ids and signal handler ids. That means e.g.uint64_t
instead ofguint64
,int
instead ofgint
,unsigned int
instead ofguint
if unsignedness is of importance,uint8_t
instead ofguchar
, and so on. -
Try to to limit line length to 80 characters, although it's not a strict limit.
-
Usage of g_autofree and g_autoptr are encouraged. The style used is
g_autofree char *text = NULL;
g_autoptr (MetaSomeThing) thing = NULL;
text = g_strdup_printf ("The text: %d", a_number);
thing = g_object_new (META_TYPE_SOME_THING,
"text", text,
NULL);
thinger_use_thing (rocket, thing);
-
Declare variables at the top of the block they are used, but avoid non-trivial logic among variable declarations. Non-trivial logic can be getting a pointer that may be
NULL
, any kind of math, or anything that may have side effects. -
Instead of boolean arguments in functions, prefer enums or flags when they're more expressive.
-
Use
g_new0()
etc instead ofg_slice_new0()
. -
Initialize and assign floating point variables (i.e.
float
ordouble
) using the formfloating_point = 3.14159
orratio = 2.0
.
Git messages
Commit messages should follow the GNOME commit message
guidelines. We require an URL
to either an issue or a merge request in each commit. Try to always prefix
commit subjects with a relevant topic, such as compositor:
or
clutter/actor:
, and it's always better to write too much in the commit
message body than too little.
License
Mutter is distributed under the terms of the GNU General Public License, version 2 or later. See the COPYING file for detalis.