Actual Window Manager [new] -

| System | What You Call It | What It Actually Is | |--------|------------------|----------------------| | Windows 11 | Desktop Window Manager (DWM) | A compositor + policy engine + input router, tightly coupled to the graphics kernel | | macOS | Quartz Compositor (part of WindowServer) | A userspace compositor + event manager + window database | | Linux (GNOME) | Mutter | A Wayland compositor + window manager + input manager | | Linux (KDE) | KWin | The same, but with pluggable window decoration and tiling scripts | | Linux (i3/sway) | i3 or Sway | A tiling window manager that is also a compositor (Sway) or relies on X11 (i3) |

Notice a pattern: the window manager is never just a manager. It is a compositor, an input router, a focus policy arbiter, and often a renderer for window borders and decorations. The pure, Platonic "window manager"—a module that only manages rectangles—exists only in textbooks and minimalist X11 setups from 1998. Part IV: The Input Gap Let us perform a small experiment in your mind. actual window manager

The answer is stranger, more fragile, and more philosophical than you think. There is no such thing as an "actual window manager"—only a series of elaborate deceptions that, when woven together, become the single most intimate piece of software you never think about. Let us begin with a technical truth: your screen has no windows. | System | What You Call It |

The window manager is the cartographer of this empty territory. It draws lines where none exist, declaring: "From pixel 320 to pixel 960, this region belongs to Firefox. From pixel 0 to pixel 320, this region belongs to your terminal." Part IV: The Input Gap Let us perform

Physically, your monitor is a grid of pixels—millions of tiny lights turning on and off. The graphics card sends a frame buffer: a rectangular array of RGB values. That buffer has no concept of a "window." It has no concept of a "taskbar," a "close button," or a "border."

This is the first deception we accept: that we are clicking "on" a window. In reality, we are clicking on the window manager's map, and the window manager is whispering to each application, "Psst—someone touched your territory." To understand the gap between "window manager" and "actual window manager," we must discuss the compositor .

The actual handoff is precise: the window manager routes the event to the correct process based on its internal map. But the map is always slightly out of date. Because your input arrives asynchronously—interrupts, device drivers, kernel queues, compositor scheduling—the window manager must guess which window is actually under the cursor at the moment of click, not when the event was recorded.