Development: Design Principles

General principles

These are some of the general principles that I try to follow throughout niri. They can be sidestepped in specific circumstances if there's a good reason.

Opening a new window should not affect the sizes of any existing windows.

This is the main annoyance with traditional tiling: you want to open a new window, but it messes with your existing window sizes. Especially when you're looking at a big window like a browser or an image editor, want to open a quick terminal for something, and it makes the big window unusably small, or reflows the content, or clips part of the window.

The usual workaround in tiling WMs is to use more workspaces: when you need a new window, you go to an empty workspace and open it there (this way, you also get your entire screen for the new window, rather than a smaller part of it).

Scrollable tiling offers an alternative: for temporary windows, you can just open them, do what you need, and close, all without messing up the other windows or having to go to a new workspace. It also lets you group together more related windows on the same workspace by having less frequently used ones scrolled out of the view.

The focused window should not move around on its own.

In particular: windows opening, closing, and resizing to the left of the focused window should not cause it to visually move.

The focused window is the window you're working in. And stuff happening outside the view shouldn't mess with what you're focused on.

Actions should apply immediately.

This is important both for compositor responsiveness and predictability, and for keeping the code sane and free of edge cases and unnecessary asynchrony.

• Things like resizing or consuming into column take effect immediately, even if the window needs time to catch up.
• An animated workspace switch makes your input go to the final workspace and window instantly, without waiting for the animation.
• Opening the overview (which has a zoom-out animation) lets you grab windows right away, and closing the overview makes your input immediately go back to the windows, without waiting for the zoom back in.

When disabled, eye-candy features should not affect the performance.

Things like animations and custom shaders do not run and are not present in the render tree when disabled. Extra offscreen rendering is avoided.

Animations specifically are still "started" even when disabled, but with a duration of 0 (this way, they end as soon as the time is advanced). This does not impact performance, but helps avoid a lot of edge cases in the code.

Eye-candy features should not cause unreasonable excessive rendering.

• For example, clip-to-geometry will prevent direct scanout in many cases (since the window surface is not completely visible). But in the cases where the surface or the subsurface is completely visible (fully within the clipped region), it will still allow for direct scanout.
• For example, animations can cause damage and even draw to an offscreen every frame, because they are expected to be short (and can be disabled). However, something like the rounded corners shader should not offscreen or cause excessive damage every frame, because it is long-running and constantly active.

Be mindful of invisible state.

This is niri state that is not immediately apparent from looking at the screen. This is not bad per se, but you should carefully consider how to reduce the surprise factor.

• For example, when a monitor disconnects, all its workspaces move to another connected monitor. In order to be able to restore these workspaces when the first monitor connects again, these workspaces keep the knowledge of which was their original monitor—this is an example of invisible state, since you can't tell it in any way by looking at the screen. This can have surprising consequences: imagine disconnecting a monitor at home, going to work, completely rearranging the windows there, then coming back home, and suddenly some random workspaces end up on your home monitor. In order to reduce this surprise factor, whenever a new window appears on a workspace, that workspace resets its original monitor to its current monitor. This way, the workspaces you actively worked on remain where they were.
• For example, niri preserves the view position whenever a window appears, or whenever a window goes full-screen, to restore it afterward. This way, dealing with temporary things like dialogs opening and closing, or toggling full-screen, becomes less annoying, since it doesn't mess up the view position. This is also invisible state, as you cannot tell by looking at the screen where closing a window will restore the view position. If taken to the extreme (previous view position saved forever for every open window), this can be surprising, as closing long-running windows would result in the view shifting around pretty much randomly. To reduce this surprise factor, niri remembers only one last view position per workspace, and forgets this stored view position upon window focus change.

Window layout

Here are some design considerations for the window layout logic.

1. If a window or popup is larger than the screen, it should be aligned in the top left corner.

   The top left area of a window is more likely to contain something important, so it should always be visible.

2. Setting window width or height to a fixed pixel size (e.g. set-column-width 1280 or default-column-width { fixed 1280; }) will set the size of the window itself, however setting to a proportional size (e.g. set-column-width 50%) will set the size of the tile, including the border added by niri.

   • With proportions, the user is looking to tile multiple windows on the screen, so they should include borders.
   • With fixed sizes, the user wants to test a specific client size or take a specifically sized screenshot, so they should affect the window directly.
   • After the size is set, it is always converted to a value that includes the borders, to make the code sane. That is, set-column-width 1000 followed by changing the niri border width will resize the window accordingly.

3. Fullscreen windows are a normal part of the scrolling layout.

   This is a cool idea that scrollable tiling is uniquely positioned to implement. Fullscreen windows aren't on some "special" layer that covers everything; instead, they are normal tiles that you can switch away from, without disturbing the fullscreen status.

   Of course, you do want to cover your entire monitor when focused on a fullscreen window. This is specifically hardcoded into the logic: when the view is stationary on a focused fullscreen window, the top layer-shell layer and the floating windows hide away.

   This is also why fullscreening a floating window makes it go into the scrolling layout.

Default config

The default config is intended to give a familiar, helpful, and not too jarring experience to new niri users. Importantly, it is not a "suggested rice config"; we don't want to startle people with full-on rainbow borders and crazy shaders.

Since we're not a complete desktop environment (and don't have the contributor base to become one), we cannot provide a fully integrated experience—distro spins are better positioned to do this. As such, new niri users are expected to read through and tinker with the default niri config.

The default config is therefore thoroughly commented with links to the relevant wiki sections. We don't include every possible option in the default config to avoid overwhelming users too much; anything overly specific or uncommon can stay on the wiki. The general rule is to include things that users are reasonably expected to want to change or know how to do. We do also advertise our more unique features though like screencast block-out-from.

We default to CSD (prefer-no-csd is commented out). This gives new users easy and familiar way to move and close windows via their titlebars, especially considering that niri doesn't have serverside titlebars (so far at least).

Focus rings are drawn fully behind windows by default. While this unfortunately messes with window transparency, which is a common source of confusion, defaulting to drawing focus rings only around windows would be even worse because it has holes inside clientside rounded corners. The ideal solution here would be to propose a Wayland protocol for windows to report their corner radius to the compositor (which would generally help for serverside decorations in different compositors).

The default focus ring is quite thick at 4 px to look well with clientside-decorated windows and be obviously noticeable, and the default gaps are also quite big at 16 px to look well with the default focus ring width.

The default input settings like touchpad tap and natural-scroll are how I believe most people want to use their computers.

Shadows default to off because they are a fairly performance-intensive shader, and because many clientside-decorated windows already draw their own shadows.

The default screenshot-path matches GNOME Shell.

Default window rules are limited to fixing known severe issues (WezTerm) and doing something the absolute majority likely wants (make Firefox Picture-in-Picture player floating—it can't do that on its own currently, maybe the pip protocol will change that).

The default binds largely come from my own experience using PaperWM, and from other compositors. They assume QWERTY. The binds are ordered in a way to gradually introduce you to different bind configuration concepts.

The general system is: if a hotkey switches somewhere, then adding Ctrl will move the focused window or column there. Adding Shift does an alternative action: for focus and movement it starts going across monitors, for resizes it starts acting on window height rather than width, etc. Workspace switching on ModU/I is one key up from ModJ/K used for window switching.

Since Alt is a modifier in nested niri, binds with explicit Alt are mainly the ones only useful on the host, for example spawning a screen locker.