add multimonitor

README.md

@@ -6,7 +6,8 @@ river 0.4 is *non-monolithic*: it ships no window management policy of its own
 `riverctl`, no `rivertile` — and instead hands the entire job to a single external
 client speaking `river-window-management-v1`. att_wm is that client. It gives you
 dwm's model on top of river: nine tags, a master/stack layout, monocle and tabbed
-layouts, and keybindings compiled into the binary.
+layouts, and keybindings compiled into the binary. On more than one monitor the
+tags are split across the screens, so every tag lives on exactly one of them.
 
 Tag and window state is published as JSON lines on a unix socket so bars such as
 [quickshell](https://quickshell.org) can render it, and `att_wmctl` drives the same
@@ -22,6 +23,9 @@ Verified working against river 0.4.5 / Zig 0.16 / quickshell 0.3.0:
 
 - tags, master / monocle / tabbed layouts, floating and fullscreen windows
 - focus cycling, `zoom`, stack reordering, per-tag layout state
+- multiple monitors, with the tag set split across them: verified on a headless
+  river with two outputs, driven over IPC — the split, moving between screens,
+  windows following their tags across, and views clamped to the screen's own tags
 - the IPC socket, `att_wmctl`, and a quickshell bar that maps as a layer surface
   and whose exclusive zone correctly shrinks the tiling area
 
@@ -149,7 +153,7 @@ if you would rather not compete with applications that bind Alt themselves.
 | `Mod+j` / `Mod+k` | Focus next / previous window |
 | `Mod+Shift+j` / `Mod+Shift+k` | Move focused window down / up the stack |
 | `Mod+Return` | Zoom — promote focused window to master |
-| `Mod+h` / `Mod+l` | Shrink / grow the master area |
+| `Mod+,` / `Mod+.` | Shrink / grow the master area |
 | `Mod+i` / `Mod+d` | Increase / decrease windows in master |
 | `Mod+t` / `Mod+m` / `Mod+u` | Master / monocle / tabbed layout |
 | `Mod+space` | Toggle between current and previous layout |
@@ -161,8 +165,8 @@ if you would rather not compete with applications that bind Alt themselves.
 | `Mod+Ctrl+Shift+1..9` | Toggle tag on focused window |
 | `Mod+0` / `Mod+Shift+0` | View all tags / put window on all tags |
 | `Mod+Tab` / `Mod+Esc` | Back to previously viewed tags |
-| `Mod+,` / `Mod+.` | Focus previous / next output |
-| `Mod+Shift+,` / `Mod+Shift+.` | Send window to previous / next output |
+| `Mod+h` / `Mod+l` | Focus the screen to the left / right |
+| `Mod+Shift+h` / `Mod+Shift+l` | Send window to the screen left / right |
 | `Mod+Left drag` | Move window (floats it) |
 | `Mod+Right drag` | Resize window |
 
@@ -212,6 +216,48 @@ keep theirs for the way back.
 
 ---
 
+## Multiple monitors
+
+The tag set is **split across the screens**: every tag lives on exactly one of
+them. With two monitors the left owns tags 1–5 and the right 6–9; with three
+they get 1–3, 4–6 and 7–9. Screens are ordered by where they sit in the output
+layout, left to right and then top to bottom — not by the order they were
+plugged in — so the arrangement follows the monitors on the desk rather than the
+cables behind it.
+
+| | |
+|---|---|
+| `Mod+h` / `Mod+l` | Move to the screen on the left / right |
+| `Mod+Shift+h` / `Mod+Shift+l` | Send the focused window there |
+| `Mod+7` | Go to the screen tag 7 lives on and show tag 7 |
+| `Mod+Shift+7` | Send the focused window to tag 7, wherever that is |
+
+Because a tag names a screen as well as a workspace, `Mod+7` and `Mod+h` are two
+ways of doing the same thing, and the tag keys alone are enough to drive the
+whole desk. Sending a window away leaves you where you are, as dwm's `tagmon`
+does; the keyboard goes to whatever is left on the screen you are still on.
+
+`Mod+0` means everything on *this* screen — a view is always clamped to the tags
+its screen owns, so no screen can be made to show another's tag.
+
+Unplugging a monitor hands its tags to the screens that remain, and the windows
+wearing those tags follow them there rather than being stranded on a tag nothing
+can show. Plug it back in and they go home. A laptop with nothing attached owns
+all nine tags and behaves exactly as it did before, which is why none of this is
+visible until there is a second screen.
+
+Set `split_tags = false` in `config.zig` for dwm's model instead: every screen
+gets a full set of nine tags of its own, and the tag keys never leave the screen
+you are on. `Mod+h`/`Mod+l` and `Mod+Shift+h`/`Mod+Shift+l` still move between
+screens and are then the only way to.
+
+Layer surfaces (bars) that do not name an output land on the focused screen.
+`warp_cursor` is worth turning on here: it pulls the pointer along when the
+keyboard moves to another screen, including onto an empty one, where there is no
+window to warp to and the cursor would otherwise be left behind.
+
+---
+
 ## Configuration
 
 att_wm is configured at compile time, like dwm. Edit `src/config.zig` and rebuild.
@@ -390,6 +436,7 @@ quickshell config uses one socket for both, avoiding a process spawn per click.
     "name": "DP-1",
     "focused": true,
     "tags": 1,
+    "owned_tags": 31,
     "occupied": 5,
     "layout": "master",
     "layout_symbol": "[]=",
@@ -411,8 +458,12 @@ quickshell config uses one socket for both, avoiding a process spawn per click.
 }
 ```
 
-`tags` and `occupied` are bitmasks — `occupied` is the set of tags holding at
-least one window, which is what dwm's bar draws its corner squares from.
+`tags`, `owned_tags` and `occupied` are bitmasks. `occupied` is the set of tags
+holding at least one window, which is what dwm's bar draws its corner squares
+from. `owned_tags` is the slice of the tag set this screen owns — see
+[Multiple monitors](#multiple-monitors) — so a bar can draw its own screen's
+tags and leave the rest to the bar on the screen they belong to. It is all nine
+when `split_tags` is off, so a bar that honours it works either way.
 `usable` is the area left after layer-shell exclusive zones, i.e. where windows
 are actually laid out.
 
@@ -464,9 +515,13 @@ quickshell -p /path/to/att_wm/quickshell
 ```
 
 `AttWm.qml` is a singleton wrapping the socket — reconnecting if att_wm restarts,
-exposing `outputs`, `focusedOutput`, `focusedTitle`, `tagActive()` and
-`tagOccupied()`, plus `send()` for commands. Reuse it in your own bar and ignore
-`shell.qml`.
+exposing `outputs`, `focusedOutput`, `focusedTitle`, `tagActive()`,
+`tagOccupied()` and `tagOwned()`, plus `send()` for commands. Reuse it in your
+own bar and ignore `shell.qml`.
+
+One bar is created per screen and each draws only the tags its screen owns, via
+`tagOwned()` — with the tag set split across monitors the other tags belong to
+the bar next door.
 
 Note that **a bar only works because att_wm binds `river_layer_shell_v1`**. river
 refuses to map layer surfaces at all unless the window manager declares support
@@ -489,7 +544,7 @@ river's identifier is shared between them.
 | --- | --- |
 | `src/Wm.zig` | Globals, the manage/render sequence state machine, actions, event loop |
 | `src/Window.zig` | Per-window state; handlers only mutate fields |
-| `src/Output.zig` | Output tags, the per-tag layout/nmaster/mfact, and the tab bar |
+| `src/Output.zig` | Output tags and which of them it owns, the per-tag layout/nmaster/mfact, and the tab bar |
 | `src/Seat.zig` | Focus, key and pointer bindings, interactive move/resize |
 | `src/InputManager.zig` | Input devices: keymaps, key repeat, libinput settings |
 | `src/layout.zig` | Pure tiling geometry — no Wayland, unit tested |