xcb-studies/xcb_read/Understanding_XRandr.md

# Understanding XRandR

XRandR (X Rotate and Resize) controls the visible aspects of what is shown on a
screen, but to do so it has a rather maddening collection of inter-related
components that help it make sense of the X Server's responsbilities.

The purpose of the X Windows System is to display _windows_, rectangular regions
on a human-visible display. In much the same way that every process on a
computer is nested in a hierarchy of parents and children all the way up to the
root process, in X every window is nested in a hierachy of parent and child
windows and atomic components all the way up to the `root` window. The root
window, in turn, belongs to a `screen`, which is the total addressable
collection of pixels for which an X11 instance is responsible.

That screen and its window are typically singular-- the screen you see before
you. But X11 is infinitely malleable. It is possible for X11 to have multiple
screens, or to have a single screen that spans multiple monitors. And it is
possible for X11 to drive those multiple monitors from one graphics card with
multiple outputs, or from multiple graphics cards installed on the same
computer.

The following objects need to be understood:

- Server: The server that you'll be communicating with.
- Connection: The connection your client has with that server.
- Screen: A virtualized collection of pixels that the server is responsible for
- CRCT: Cathode Ray Tube Controller, what we now call a 'graphics card', that
  the server uses to show a portion (possibly a portion as large as 100%) of the
  screen on a monitor.
- Output: The physical connection between a CRTC and a monitor. Depending on the
  XRandR protocol and the modernity of the monitor, XRandR can probably extract
  information about the monitor from that monitor.  

And the following facts:

- A screen has both CRTCs and Outputs.
- Although a CRTC can have an array of Outputs, at the moment each CRTC supports
  only one at a time.  If a graphics card has multiple (phyisical) connectors,
  each connector has its own CRTC.  As [How Video Cards
  Work](https://www.x.org/wiki/Development/Documentation/HowVideoCardsWork/)... [TK]
- An output can have multiple CRTCs... but usually has only one.
Moving the 'learning xcb reading' into its own folder. This matches the learning process that I describe in rigged_regex. Step by step, recording everything multiple times and in multiple ways, so that all the learning that I care about is preserved. There's XCB in here, and some C++ (mostly around `unique_ptr`). 2022-04-15 21:41:03 +00:00			`# Understanding XRandR`

			`XRandR (X Rotate and Resize) controls the visible aspects of what is shown on a`
			`screen, but to do so it has a rather maddening collection of inter-related`
			`components that help it make sense of the X Server's responsbilities.`

			`The purpose of the X Windows System is to display _windows_, rectangular regions`
			`on a human-visible display. In much the same way that every process on a`
			`computer is nested in a hierarchy of parents and children all the way up to the`
			`root process, in X every window is nested in a hierachy of parent and child`
			windows and atomic components all the way up to the `root` window. The root
			window, in turn, belongs to a `screen`, which is the total addressable
			`collection of pixels for which an X11 instance is responsible.`

			`That screen and its window are typically singular-- the screen you see before`
			`you. But X11 is infinitely malleable. It is possible for X11 to have multiple`
			`screens, or to have a single screen that spans multiple monitors. And it is`
			`possible for X11 to drive those multiple monitors from one graphics card with`
			`multiple outputs, or from multiple graphics cards installed on the same`
			`computer.`

			`The following objects need to be understood:`

			`- Server: The server that you'll be communicating with.`
			`- Connection: The connection your client has with that server.`
			`- Screen: A virtualized collection of pixels that the server is responsible for`
			`- CRCT: Cathode Ray Tube Controller, what we now call a 'graphics card', that`
			`the server uses to show a portion (possibly a portion as large as 100%) of the`
			`screen on a monitor.`
			`- Output: The physical connection between a CRTC and a monitor. Depending on the`
			`XRandR protocol and the modernity of the monitor, XRandR can probably extract`
			`information about the monitor from that monitor.`

			`And the following facts:`

			`- A screen has both CRTCs and Outputs.`
			`- Although a CRTC can have an array of Outputs, at the moment each CRTC supports`
			`only one at a time. If a graphics card has multiple (phyisical) connectors,`
			`each connector has its own CRTC. As [How Video Cards`
			`Work](https://www.x.org/wiki/Development/Documentation/HowVideoCardsWork/)... [TK]`
			`- An output can have multiple CRTCs... but usually has only one.`