Linux 图形子系统
My old posts:
- http://fkpwolf.net/2012/11/03/framebuffer-on-raspberry-pi/
- http://fkpwolf.net/2012/12/28/light-weight-window-for-raspberry-pi/
Gnome 3 has include clutter https://wiki.gnome.org/Projects/Clutter
ldd /usr/bin/gnome-shell | grep -i clutter
libclutter-1.0.so.0 => /usr/lib/x86_64-linux-gnu/libclutter-1.0.so.0
http://www.tuxradar.com/content/clutter-beginners-tutorial It will distort screen to low screen resolution in hiDPI mode.
debug Gnome : You currently run it by pressing Alt-F2, typing lg, then Return. https://wiki.gnome.org/Projects/GnomeShell/LookingGlass
Gnome Shell use Mutter as window manager. Mutter is a Wayland compositor like Weston. Mutter use Clutter as graphics library. A new era for Linux’s low-level graphics - Part 1
How to know whether Wayland or X11 is being used. https://unix.stackexchange.com/questions/202891/how-to-know-whether-wayland-or-x11-is-being-used
Does your application run on Wayland natively, or uses XWayland (X11 compatibility layer)? https://fedoraproject.org/wiki/How_to_debug_Wayland_problems#Does_your_application_run_on_Wayland_natively.2C_or_uses_XWayland_.28X11_compatibility_layer.29.3F
https://www.phoronix.com/scan.php?page=news_item&px=GTK-Vulkan-Wayladdnd-Setup
Programming Wayland Clients，这本书不错，很多 hello world 的代码。
https://jan.newmarch.name/Wayland/EGL/ 编译方法 cc -o egl egl.c -lwayland-client -lEGL -lwayland-egl
编译好的程序如果在 text mode 下运行，会报 can’t connect display 的错误，但是如何在运行完 mutter 后运行程序呢？可能这里的方法会有作用。
Free and open-source graphics device driver lists some useful overview information.
From https://wayland.freedesktop.org/architecture.html
From https://en.wikipedia.org/wiki/Wayland_(display_server_protocol) 为什么要单独出 KMS 呢？全部给 DRM 不好？ Wayland compositor and its clients use EGL to draw directly into the framebuffer. 既然如此，wayland就做很少事情了？但是 wayland 应该还是封装了 EGL，比如上面的 W2EGL glue code。上面的 2，3是消息。 https://en.wikipedia.org/wiki/Evdev Linux kernel → libevdev → libinput → Weston → Wayland client, xorg 也用了 libevdev，所以输入子系统这块基本是相同的。
[fan@intelway ~]$ lsof /usr/lib/libevdev.so
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
gnome-she 1205 fan mem REG 8,1 105520 3439743 /usr/lib/libevdev.so.2.1.21
DRM 允许多个程序使用统一的接口来同时使用 GPU。DRM 获得对 Video Card 的独占访问权限，它负责初始化和维护命令队列、Video RAM 以及其他相关的硬件资源。https://book.iyounix.com/device-porting/drm/linux-drm-1-display-server-history.html. amd-gpu 是AMD显卡的内核驱动模块，”One of the key interfaces used by the amdgpu module is the Direct Rendering Manager (DRM) subsystem, which provides a standardized interface for user-space applications to access the GPU hardware. The amdgpu driver registers itself as a DRM driver, which allows it to handle requests from user-space applications that use the OpenGL or Vulkan APIs for 3D graphics rendering.” by ChatGPT. I can see drm_buddy and drm_display_helper modules depend on amd_gpu module. For Intel graphic device like Arc A750, the driver is i915.
DRI 似乎只有 X 才会使用
https://en.wikipedia.org/wiki/Framebuffer这个是显卡的设备
https://en.wikipedia.org/wiki/Mesa_(computer_graphics) 开源的显卡驱动，是OpenGL, ES, EGL, Vulkan的软件实现。运行 glxinfo 可以得到： OpenGL vendor string: Intel Open Source Technology Center OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Server EGL 是 OpenGL ES 渲染 API 和本地窗口系统(native platform window system)之间的一个中间接口层，通过调用 eglCreateWindowSurface 提供给 OpenGL 一个 surface / 画布，还做 front buffer 和 back buffer 之间的切换 eglSwapBuffer。如此看来 EGL 做了相当多的事情了，而 Wayland 只是处理了鼠标键盘事件？
Compositor
https://en.wikipedia.org/wiki/Compositing_window_manager A compositing window manager, or compositor, is a window manager that provides applications with an off-screen buffer for each window. The window manager composites the window buffers into an image representing the screen and writes the result into the display memory. 对于 EGL 部分，就交给 libGL 了。https://en.wikipedia.org/wiki/Mutter_(software) Gnome3 默认的管理器。 总的来说，compositor 就是支持多窗口界面了。Now there is no X daemon running. No C-S stuff. But how to make sure Mutter running/working? “lsof | grep mutter” say mutter used by gnome-shell as library. So just directly run gnome-shell (if installed GDM, GDM will start gnome-shell)? Even the libwayland-server is a library! All direct call, no message? input event is still sent by IPC as C-S style as X, but rendering is directly: application directly call EGL. There is command ‘mutter’. Why it exit after Gnome startup? In text mode, can run ‘mutter –wayland’. Just a blank window. To enter text mode, first temporary stop GDM, then ctl+alt+f2. Plasma uses KWin(https://community.kde.org/KWin/Wayland).
这个IPC应该需要有个常驻的server进程吧？还是全部是callback钩子？
On Ubuntu 17.10,
fan@fan-APLD-MINI:~$ dpkg-query -L libmutter-1-0
/.
/usr
/usr/lib
/usr/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu/libmutter-1.so.0.0.0
/usr/lib/x86_64-linux-gnu/mutter
/usr/lib/x86_64-linux-gnu/mutter/libmutter-clutter-1.so
/usr/lib/x86_64-linux-gnu/mutter/libmutter-cogl-1.so
/usr/lib/x86_64-linux-gnu/mutter/libmutter-cogl-pango-1.so
/usr/lib/x86_64-linux-gnu/mutter/libmutter-cogl-path-1.so
/usr/share
/usr/share/doc
/usr/share/doc/libmutter-1-0
/usr/share/doc/libmutter-1-0/changelog.Debian.gz
/usr/share/doc/libmutter-1-0/copyright
/usr/lib/x86_64-linux-gnu/libmutter-1.so.0
fan@fan-APLD-MINI:~$ lsof /usr/lib/x86_64-linux-gnu/libmutter-1.so.0
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
Output information may be incomplete.
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
gnome-she 1092 fan mem REG 179,2 1366928 1182432 /usr/lib/x86_64-linux-gnu/libmutter-1.so.0.0.0
GNOME Shell is written in C and JavaScript as a plugin for Mutter.
fan@fan-APLD-MINI:~$ apt-cache search libwayland
libwayland-bin - wayland compositor infrastructure - binary utilities
libwayland-client0 - wayland compositor infrastructure - client library
libwayland-cursor0 - wayland compositor infrastructure - cursor library
libwayland-dev - wayland compositor infrastructure - development files
libwayland-doc - wayland compositor infrastructure - documentation files
libwayland-egl1-mesa - implementation of the Wayland EGL platform -- runtime
libwayland-server0 - wayland compositor infrastructure - server library
fan@fan-APLD-MINI:~$ apt-cache search libgl|grep mesa
libgl1-mesa-dev - free implementation of the OpenGL API -- GLX development files
libgl1-mesa-dri - free implementation of the OpenGL API -- DRI modules
libgl1-mesa-glx - free implementation of the OpenGL API -- GLX runtime
libglapi-mesa - free implementation of the GL API -- shared library
libgles2-mesa - free implementation of the OpenGL|ES 2.x API -- runtime
libgles2-mesa-dev - free implementation of the OpenGL|ES 2.x API -- development files
libglu1-mesa - Mesa OpenGL utility library (GLU)
libglu1-mesa-dev - Mesa OpenGL utility library -- development files
libglw1-mesa - GL widget library for Athena and Motif -- runtime
libglw1-mesa-dev - GL widget library for Athena and Motif -- development files
有了 DRM 之后，x client 可以直接访问 drm，这样一来 x windows 似乎和 wayland 差不多了。
这个对比更为清楚。主要是对于普通 X11 application，所有的渲染操作都是 server 完成，client 只发送消息，这属于典型 C/S 模式，性能会有额外开销。Wayland 则是自己直接通过调用EGL来渲染，渲染完成后用wayland protocal通知compositor特定区域已经被更新。所以Wayland protocol 只是high-level API，用来处理显示和用户输入。
https://wiki.archlinux.org/title/wayland list of different Compositors: Tiling and Stacking. What are the best Wayland compositors? shows the best one is Sway.
树莓派
https://github.com/anholt/mesa/wiki/VC4 Enabling the driver is controlled using raspi-config. Select Advanced Options option and then GL Driver. Raspbian only supports vc4 on the Raspberry PI 2 and later. The driver supports Raspberry Pi 1, but raspi-config refuses to do it.
Raspberry Pi OS now uses Wayland (instead of X11) with Wayfire (instead of Mutter) by default on Raspberry Pi 4 and Raspberry Pi 5. https://wayfire.org/
https://www.collabora.com/news-and-blog/blog/2016/06/03/running-weston-on-a-raspbian/ 只有少量程序可以运行
Evolution in Flatpak https://wiki.gnome.org/Apps/Evolution/Flatpak As of Evolution release 3.30.0, users can build the latest stable (or development) version of Evolution using Flatpak.As of Evolution release 3.30.0, users can build the latest stable (or development) version of Evolution using Flatpak. 沙箱运行环境，桌面这么大的也可以运行在沙箱里面？用来做开发测试倒是蛮好的。
postmarketOS，专门为老手机提供最新 Linux 系统，User-Interfaces，其使用的默认窗口管理系统是 Weston。有些驱动比如无线和蓝牙是闭源的，不知道图像驱动是不是也是。
Pure Wayland toolkit prototype supports in OpenJDK