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86 lines
3.5 KiB
Markdown
86 lines
3.5 KiB
Markdown
# Architecture
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This document describes the high-level design of wlroots. wlroots is modular:
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each module can be used mostly independently from the rest of wlroots. For
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instance, some wlroots-based compositors only use its backends, some only use
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its protocol implementations.
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## Backends
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Backends are responsible for exposing input devices and output devices.
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wlroots provides DRM and libinput backends to directly drive physical
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devices, Wayland and X11 backends to run nested inside another compositor,
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and a headless backend. A special "multi" backend is used to combine together
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multiple backends, for instance DRM and libinput. Compositors can also
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implement their own custom backends if they have special needs.
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Input devices such as pointers, keyboards, touch screens, tablets, switches
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are supported. They emit input events (e.g. a keyboard key is pressed) which
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compositors can handle and forward to Wayland clients.
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Output devices are tasked with presenting buffers to the user. They also
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provide feedback, for instance presentation timestamps. Some backends support
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more advanced functionality, such as displaying multiple buffers (e.g. for the
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cursor image) or basic 2D transformations (e.g. rotation, clipping, scaling).
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## Renderers
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Renderers provide utilities to import buffers submitted by Wayland clients,
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and a basic 2D drawing API suitable for simple compositors. wlroots provides
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renderer implementations based on OpenGL ES 2, Vulkan and Pixman. Just like
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backends, compositors can implement their own renderers, or use the graphics
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APIs directly.
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To draw an image onto a buffer, compositors will first need to create a
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texture, representing a source of pixels the renderer can sample from. This can
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be done either by uploading pixels from CPU memory, or by importing already
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existing GPU memory via DMA-BUFs. Compositors can then create a render pass
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and submit drawing operations. Once they are done drawing, compositors can
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submit the rendered buffer to an output.
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## Protocol implementations
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A number of Wayland interface implementations are provided.
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### Plumbing protocols
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wlroots ships unopinionated implementations of core plumbing interfaces, for
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instance:
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- `wl_compositor` and `wl_surface`
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- `wl_seat` and all input-related interfaces
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- Buffer factories such as `wl_shm` and linux-dmabuf
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- Additional protocols such as viewporter and presentation-time
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### Shells
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Shells give a meaning to surfaces. There are many kinds of surfaces:
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application windows, tooltips, right-click menus, desktop panels, wallpapers,
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lock screens, on-screen keyboards, and so on. Each of these use-cases is
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fulfilled with a shell. wlroots supports xdg-shell for regular windows and
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popups, Xwayland for interoperability with X11 applications, layer-shell for
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desktop UI elements, and more.
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### Other protocols
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Many other protocol implementations are included, for instance:
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- xdg-activation for raising application windows
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- idle-inhibit for preventing the screen from blanking when the user is
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watching a video
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- ext-idle-notify for notifying when the user is idle
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## Helpers
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wlroots provides additional helpers which can make it easier for compositors to
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tie everything together:
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- `wlr_output_layout` organises output devices in the physical space
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- `wlr_cursor` stores the current position and image of the cursor
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- `wlr_scene` provides a declarative way to display surfaces
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## tinywl
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tinywl is a minimal wlroots compositor. It implements basic stacking window
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management and only supports xdg-shell. It's extensively commented and is a
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good learning resource for developers new to wlroots.
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