xorg-xorgproto/protocol.txt

	The X Resize, Rotate and Reflect Extension
		     Version 1.2
		       2006-4-13

		      Jim Gettys
	          Jim.Gettys@hp.com
	     Cambridge Research Laboratory
		        HP Labs
	        Hewlett Packard Company

	             Keith Packard
	         keith.packard@intel.com
	      Open Source Technology Center
		   Intel Corporation

1. Introduction

The X Resize, Rotate and Reflect Extension, called RandR for short,
brings the ability to resize, rotate and reflect the root window of a
screen.  It is based on the X Resize and Rotate Extension as specified
in the Proceedings of the 2001 Usenix Technical Conference [RANDR].

RandR as implemented and integrated into the X server differs in
one substantial fashion from the design discussed in that paper: that
is, RandR 1.0 does not implement the depth switching described in that
document, and the support described for that in the protocol in that
document and in the implementation has been removed from the
protocol described here, as it has been overtaken by events.

These events include:
      o Modern toolkits (in this case, GTK+ 2.x) have progressed to the point
        of implementing migration between screens of arbitrary depths
      o The continued advance of Moore's law has made limited amounts of VRAM
        less of an issue, reducing the pressure to implement depth switching
	on laptops or desktop systems
      o The continued decline of legacy toolkits whose design would have
        required depth switching to support migration
      o The lack of depth switchin implementation experience in the 
        intervening time, due to events beyond our control

Additionally, the requirement to support depth switching might
complicate other re-engineering of the device independent part of the
X server that is currently being contemplated.
	
Rather than further delaying RandR's widespread deployment for a feature
long wanted by the community (resizing of screens, particularly on laptops),
or the deployment of a protocol design that might be flawed due to lack of
implementation experience, we decided to remove depth switching from the
protocol.  It may be implementated at a later time if resources and
interests permit as a revision to the protocol described here, which will
remain a stable base for applications.  The protocol described here has been
implemented in the main X.org server, and more fully in the hw/kdrive
implementation in the distribution, which fully implements resizing,
rotation and reflection.

1.2 Introduction to version 1.2 of the extension

One of the significant limitations found in version 1.1 of the RandR
protocol was the inability to deal with the Xinerama model where multiple
monitors display portions of a common underlying screen. In this environment,
the size of the 'porthole' shown by each monitor is independent of the
overall size of the screen, and the porthole may be located anywhere within
the screen.

The effect is to decouple the reported size of the screen from the size
presented by each monitor, and to permit multiple monitors to present
information for a single screen.

To extend RandR for this model, we separate out the monitor and screen
configuration information and permit them to be configured separately. For
compatibility with the 1.1 version of the protocol, we make the 1.1 requests
simultaneously affect both the screen and the (presumably sole) monitor.

Additional requests and events are provided for this new functionality.

2. Acknowlegements

Our thanks to the contributors to the design found on the xpert mailing
list, in particular:

Alan Hourihane for work on the early implementation
Andrew C. Aitchison for help with the XFree86 DDX implementation
Andy Ritger for early questions about how mergefb/Xinerama work with RandR
Carl Worth for editing the specification and Usenix paper
David Dawes for XFree86 DDX integration work
Thomas Winischhofer for the hardware-accelerated SiS rotation implementation

2. Screen change model

Screens may change dynamically, either under control of this
extension, or due to external events. Examples include: monitors being
swapped, you pressing a button to switch from internal display to an
external monitor on a laptop, or, eventually, the hotplug of a display
card entirely on busses such as Cardbus which permit hot-swap (which
will require other work in addition to this extension).

Since the screen configuration is dynamic and asynchronous to the
client and may change at any time RandR provides mechanisms to ensure
that your clients view is up to date with the configuration
possibilities of the moment and enforces applications that wish to
control the configuration to prove that their information is up to
date before honoring requests to change the screen configuration (by
requiring a timestamp on the request).

Interested applications are notified whenever the screen configuration
changes, providing the current size of the screen and subpixel order
(see the Render extension [RENDER]), to enabel proper rendering of
subpixel decimated client text to continue, along with a time stamp of
the configuration change.  A client must refresh its knowledge of the
screen configuration before attempting to change the configuration
after a notification, or the request will fail.

To avoid multiplicative explosion between orientation, reflection
and sizes, the sizes are only those sizes in the normal (0) rotation.

Rotation and reflection and how they interact can be confusing.  In
Randr, the coordinate system is rotated in a counter-clockwise
direction relative to the normal orientation.  Reflection is along the
window system coordinate system, not the physical screen X and Y axis,
so that rotation and reflection do not interact.  The other way to
consider reflection is to is specified in the "normal" orientation,
before rotation, if you find the other way confusing.

We expect that most clients and toolkits will be oblivious to changes
to the screen stucture, as they generally use the values in the
connections Display structure directly.  By toolkits updating the
values on the fly, we believe pop-up menus and other pop up windows
will position themselves correctly in the face of screen configuration
changes (the issue is ensuring that pop-ups are visible on the
reconfigured screen).

3. Data Types

The subpixel order is shared with the Render extension, and is
documented there.  The only datatype defined is the screen size,
defined in the normal (0 degree) orientation.

4. Errors

There are no new error types defined by this extension.

5. Protocol Types

RRCONFIGSTATUS {
	Success
	InvalidConfigTime
	InvalidTime
	Failed }
ROTATION {
	 Rotate_0
	 Rotate_90
	 Rotate_180
	 Rotate_270
	 Reflect_X
	 Reflect_Y }

RRSELECTMASK { RRScreenChangeNotifyMask }

SIZEID { CARD16 }

SUBPIXELORDER { SubPixelUnknown		The subpixel order uses the Render
	      SubPixelHorizontalRGB	extensions definitions; they are here
	      SubPixelHorizontalBGR	only for convenience.
	      SubPixelVerticalRGB
	      SubPixelVerticalBGR
	      SubPixelNone }

SCREENSIZE {    
	widthInPixels, heightInPixels: CARD16
	widthInMillimeters, heightInMillimeters: CARD16 }

REFRESH {
	rates: LISTofCARD16 }

6. Extension Initialization

The name of this extension is "RANDR".

RRQueryVersion
	client-major-version:	CARD32
	client-minor-version:	CARD32
	->
	major-version:		CARD32
	minor-version:		CARD32

	The client sends the highest supported version to the server
	and the server sends the highest version it supports, but no
	higher than the requested version.  Major versions changes can
	introduce incompatibilities in existing functionality, minor
	version changes introduce only backward compatible changes.
	It is the clients responsibility to ensure that the server
	supports a version which is compatible with its expectations.

7. Extension Requests

RRSelectInput
	window: WINDOW
	enable: SETofRRSELECTMASK

	Errors: Window, Value

	If 'enable' is RRScreenChangeNotifyMask, RRScreenChangeNotify events
	will be sent anytime the screen configuration changes, either from
	this protocol extension, or due to detected external screen
	configuration changes. RRScreenChangeNotify may also be sent when
	this request executes if the screen configuration has changed since
	the client connected, to avoid race conditions.

RRSetScreenConfig
	drawable: DRAWABLE
	timestamp: TIMESTAMP
	config-timestamp: TIMESTAMP
	sizeID: SIZEID
	rotation: ROTATION
	rate: CARD16

	->

	status: RRCONFIGSTATUS
	new-timestamp: TIMESTAMP
	config-timestamp: TIMESTAMP
	root: WINDOW
	subpixelOrder: SUBPIXELORDER

	Errors: Value, Match

	If 'timestamp' is less than the time when the configuration was last
	successfully set, the request is ignored and InvalidTime returned in
	status.
	
	If 'config-timestamp' is not equal to when the server's screen
	configurations last changed, the request is ignored and
	InvalidConfigTime returned in status.  This could occur if the
	screen changed since you last made a RRGetScreenInfo request,
	perhaps by a different piece of display hardware being installed.
	Rather than allowing an incorrect call to be executed based on stale
	data, the server will ignore the request.

	'rate' contains the desired refresh rate. If it is zero, the server
	selects an appropriate rate.

	This request may fail for other indeterminate reasons, in which case
	'status' will be set to Failed and no configuration change will be
	made.
	
	This request sets the screen to the specified size, rate, rotation
	and reflection.

	When this request succeeds, 'status' contains Success and the
	requested changes to configuration will have been made.
	
	'new-time-stamp' contains the time at which this request was
	executed.
	
	'config-timestamp' contains the time when the possible screen
	configurations were last changed.
	
	'root' contains the root window for the screen indicated by the
	drawable.

	'subpixelOrder' contains the resulting subpixel order of the screen
	to allow correct subpixel rendering.

	Value errors are generated when 'rotation', 'rate' or 'sizeID' are
	invalid.

RRGetScreenInfo
	window: WINDOW

	->	

	rotations: SETofROTATION
	root: WINDOW
	timestamp: TIMESTAMP
	config-timestamp: TIMESTAMP
	sizeID: SIZEID
	rotation: ROTATION
	rate: CARD16
	sizes: LISTofSCREENSIZE
	refresh: LISTofREFRESH

	where:

	Errors: Window

	RRGetScreenInfo returns information about the current and available
	configurations for the screen associated with 'window'.

	'rotations' contains the set of rotations and reflections supported
	by the screen.

	'root' is the root window of the screen.
	
	'config-timestamp' indicates when the screen configuration
	information last changed: requests to set the screen will fail
	unless the timestamp indicates that the information the client
	is using is up to date, to ensure clients can be well behaved
	in the face of race conditions. 
	
	'timestamp' indicates when the configuration was last set.
	
	'sizeID' indicates which size is active.

	'rate' is the current refresh rate.  This is zero when the refresh
	rate is unknown or on devices for which refresh is not relevant.

	'sizes' is the list of possible frame buffer sizes (at the normal
	orientation. Each size indicates both the linear physical size of
	the screen and the pixel size.

	'refresh' is the list of refresh rates for each size. Each element
	of 'sizes' has a cooresponding element in 'refresh'.  An empty list
	indicates no known rates, or a device for which refresh is not
	relevant.

	The default size of the screen (the size that would become the
	current size when the server resets) is the first size in the
	list.

7.1. Extension Requests added in version 1.2 of the extension

As introduced above, version 1.2 of the extension splits the screen size
from the monitor configuration, permitting the subset of the screen
presented by multiple monitors to be configured. As a separate notion, the
size of the screen itself may be arbitrarily configured within a defined
range.

RRGetScreenSizeRange
	drawable: DRAWABLE
	
	->

	CARD16	minWidth, minHeight
	CARD16	maxWidth, maxHeight

	Errors: Drawable

	Returns the range of possible screen sizes. The screen may be set to
	any size within this range.

RRSetScreenSize
	drawable: DRAWABLE
	timestamp: TIMESTAMP
	config-timestamp: TIMESTAMP
	width: CARD16
	height: CARD16

	Errors: Drawable, Match, Value

	Sets the screen to the specified size. 'width' and 'height' must be
	within the range allowed by GetScreenSizeRanges, otherwise a Value
	error results. All active monitors must be configured to display a
	subset of the specified size, else a Match error results.

RRGetMonitorInfo
	drawable: DRAWABLE

	->

	root: WINDOW
	monitors: LISTofMONITOR

	where:

	MONITOR {
		name: STRING
		timestamp: TIMESTAMP
		config-timestamp: TIMESTAMP
		x, y: INT16
		sizeID: SIZEID or Disabled
		rotation: ROTATION
		rate: CARD16
		rotations: SETofROTATION
		defaultSizeID: SIZEID or Disabled
		sizes: LISTofSCREENSIZE
		refresh: LISTofREFRESH
	}

	Errors: Drawable

	RRGetMonitorInfo returns information about the current and available
	configurations for all monitors connected to the screen associated
	with 'window'.

	'root' is the root window of the screen.
	
	'timestamp' indicates when the configuration was last set.
	
	'config-timestamp' indicates when the screen configuration
	information last changed: requests to set the screen will fail
	unless the timestamp indicates that the information the client
	is using is up to date, to ensure clients can be well behaved
	in the face of race conditions. 
	
	'x' and 'y' indicate the position of this monitor within the screen
	region. They will be set to 0 when the monitor is disabled.
	
	'sizeID' indicates which size is active, or 'Disabled' indicating
	that the monitor has been disabled and is not displaying the screen
	contents.

	'rotation' indicates the active rotation. It is set to Rotate_0
	when the monitor is disabled.
	
	'rate' is the current refresh rate.  This is zero when monitor is
	disabled, when the refresh rate is unknown or on devices for which
	refresh is not relevant.

	'rotations' contains the set of rotations and reflections supported
	by the monitor.

	'defaultSizeID' is the size the monitor is set to at server reset
	time.

	'sizes' is the list of possible displayed sizes (with rotation set
	to Rotate_0). Each size indicates both the linear physical size of
	the monitor and the pixel size of the displayed area.

	'refresh' is the list of refresh rates for each size. Each element
	of 'sizes' has a cooresponding element in 'refresh'.  An empty list
	indicates no known rates, or a device for which refresh is not
	relevant.

RRSetMonitorConfig
	drawable: DRAWABLE
	monitor: CARD32
	timestamp: TIMESTAMP
	config-timestamp: TIMESTAMP
	x,y: INT16
	sizeID: SIZEID
	rotation: ROTATION
	rate: CARD16

	->

	status: RRStatus
	new-timestamp: TIMESTAMP
	config-timestamp: TIMESTAMP
	root: WINDOW
	subpixelOrder: SUBPIXELORDER

	Errors: Drawable, Value, Match

	If the timestamp in this request is less than the time when
	the configuration was last successfully set, the request is
	ignored and False returned in success.  If the
	config-timestamp in this request is not equal to when the
	server's screen configurations last changed, the request is
	ignored and False returned in success.  This could occur if
	the screen changed since you last made a RRGetScreenInfo
	request, perhaps by a different piece of display hardware
	being installed.  Rather than allowing an incorrect call to be
	executed based on stale data, the server will ignore the
	request.

	If rate is zero, the server selects an appropriate rate.

	If the request succeeds, this request sets the screen to the
	specified size, rate, rotation and reflection. If the requests
	succeeds, the new-time-stamp is returned containing the time
	when the screen configuration was changed and config-timestamp
	is returned to indicate when the possible screen
	configurations were last changed, and success is set to True.
	The root window for the screen indicated by the drawable
	argument is also returned, along with the subpixel order, to
	allow correct subpixel rendering.

	Value errors are generated if the rotation is not an
	allowed rotation. Value errors are generated, if, when the
	timestamps would allow the operation to succeed, or size-index
	are not possible (out of range).

8. Extension Events

Clients MAY select for ConfigureNotify on the root window to be
informed of screen changes.  This may be advantageous if all your
clients need to know is the size of the root window, as it avoids
round trips to set up the extension.

RRScreenChangeNotify is sent if RRSelectInput has requested it
whenever properties of the screen change, which may be due to external
factors, such as recabling a monitor, etc.

RRScreenChangeNotify

	rotation: ROTATION;		new rotation
	sequenceNumber: CARD16		low 16 bits of request's seq. number
	timestamp: TIMESTAMP		time screen was changed
	configTimestamp: TIMESTAMP	time config data was changed
	root: WINDOW			root window of screen
	window: WINDOW			window requesting notification
	sizeID: SIZEID			new ID of size
	subpixelOrder: SUBPIXELORDER	order of subpixels
	widthInPixels: INT16
	heightInPixels: INT16
	widthInMillimeters: INT16
	heightInMillimeters: INT16

	This event is generated whenever the screen configuration is changed
	and sent to requesting clients. 'timestamp' indicates when the
	screen configuration was changed.  'configTimestamp' says when the
	last time the configuration was changed. 'root' is the root of the
	screen the change occurred on, 'window' is window selecting for this
	event. 'sizeID' contains the index of the current size.

	This event is sent whenever the screen's configuration changes
	or if a new screen configuration becomes available that was
	not available in the past.  In this case (config-timestamp in
	the event not being equal to the config-timestamp returned in
	the last call to RRGetScreenInfo), the client MUST call
	RRGetScreenInfo to update its view of possible screen
	configurations to have a correct view of possible screen
	organizations.

	Clients which select screen change notification events may be
	sent an event immediately if the screen configuration was
	changed between when they connected to the X server and
	selected for notification.  This is to prevent a common race
	that might occur on log-in, where many applications start up
	just at the time when a display manager or log in script might
	be changing the screen size or configuration.

9. Extension Versioning

The RandR extension was developed in parallel with the implementation
to ensure the feasibility of various portions of the design.  As
portions of the extension are implemented, the version number of the
extension has changed to reflect the portions of the standard provied.
This document describes the version 1.0 of the specification, the
partial implementations have version numbers less than that.  Here's a
list of what each version before 1.0 implemented:

	0.0: This prototype implemented resize and rotation in the
	     TinyX server Used approximately the protocol described in
	     the Usenix paper.  Appeared in the TinyX server in
	     XFree86 4.2, but not in the XFree86 main server.

	0.1: Added subpixel order, added an event for subpixel order.
	     This version was never checked in to XFree86 CVS.

	1.0: Implements resize, rotation, and reflection.  Implemented
	     both in the XFree86 main server (size change only at this
	     date), and fully (size change, rotation, and reflection)
	     in XFree86's TinyX server.

	1.1: Added refresh rates

	1.2: Separate out screens from monitors

Compatibility between 0.0 and 1.0 was *NOT* preserved, and 0.0 clients
will fail against 1.0 servers.  The wire encoding op-codes were
changed for GetScreenInfo to ensure this failure in a relatively
graceful way.  Version 1.1 servers and clients are cross compatible with
1.0.  Version 1.1 is considered to be stable and we intend upward
compatibility from this point.

Appendix A. Protocol Encoding

Syntactic Conventions

This document uses the same syntactic conventions as the core X
protocol encoding document.


A.1 Common Types

	SETofROTATION

	0x0001	Rotate_0
	0x0002	Rotate_90
	0x0004	Rotate_180
	0x0008	Rotate_270
	0x0010	Reflect_X
	0x0020	Reflect_Y


	SETofRRSELECTMASK

	0x0001	RRScreenChangeNotifyMask


A.2 Protocol Requests


Opcodes 0x1 and 0x3 were used in the 0.0 protocols, and will return
errors if used in version 1.0.

	RRQueryVersion

	1	CARD8			major opcode
	1	0x01			RandR opcode
	2	3			length
	4	CARD32			major version
	4	CARD32			minor version
	->
	1	1			Reply
        1				unused
	2	CARD16			sequence number
	4	0			reply length
	1	CARD32			major version
        1	CARD32			minor version

	RRSetScreenConfig

	1	CARD8			major opcode
	1	0x02			RandR opcode
	2	5			length
	4	DRAWABLE		drawable on screen to be configured
	4	TIMESTAMP		timestamp
	2	SIZEID			size id
	2	ROTATION		rotation/reflection
	2	CARD16			refresh rate (1.1 only)
	2	CARD16			pad
	->
	1	1			Reply
	1	CARD8			status
		0x0 RRSetConfigSuccess
		0x1 RRSetConfigInvalidConfigTime
		0x2 RRSetConfigInvalidTime
		0x3 RRSetConfigFailed
	2	CARD16			sequence number
	4	0			reply length
	4	TIMESTAMP		new timestamp
	4	TIMESTAMP		new configuration timestamp
	4	WINDOW			root
	2	SUBPIXELORDER		subpixel order defined in Render
	2	CARD16			pad4
	4	CARD32			pad5
	4	CARD32			pad6

	
	RRSelectInput

	1	CARD8			major opcode
	1	0x04			RandR opcode
	2	3			length
	4	WINDOW			window
	2	SETofRRSELECTMASK	enable
	2	CARD16			pad


	RRGetScreenInfo

	1	CARD8			major opcode
	1	0x05			RandR opcode
	2	2			length
	4	WINDOW			window
	->
	1	1			Reply
	1	CARD8			set of Rotations
	2	CARD16			sequence number
	4	0			reply length
	4	WINDOW			root window
	4	TIMESTAMP		timestamp
	4	TIMESTAMP		config timestamp
	2	CARD16			number of SIZE following
	2	SIZEID			sizeID
	2	ROTATION		current rotation and reflection
	2	CARD16			rate (1.1)
	2	CARD16			length of rate info (number of CARD16s)
	2	CARD16			pad

	SIZE
	2	CARD16			width in pixels
	2	CARD16			height in pixels
	2	CARD16			width in millimeters
	2	CARD16			height in millimeters

	REFRESH
	2	CARD16			number of rates (n)
	2n	CARD16			rates

A.2 Protocol Event

	RRScreenChangeNotify

	1	Base + 0		code
	1	ROTATION		new rotation and reflection
	2	CARD16			sequence number
	4	TIMESTAMP		timestamp
	4	TIMESTAMP		configuration timestamp
	4	WINDOW			root window
	4	WINDOW			request window
	2	SIZEID			size ID
	2	SUBPIXELORDER		subpixel order defined in Render
	2	CARD16			width in pixels
	2	CARD16			height in pixels
	2	CARD16			width in millimeters
	2	CARD16			height in millimeters


Bibliography

[RANDR] Gettys, Jim and Keith Packard, "The X Resize and Rotate
	Extension - RandR", Proceedings of the 2001 USENIX Annual
	Technical Conference, Boston, MA

[RENDER] 
	Packard, Keith, "The X Rendering Extension", work in progress,
	documents found in xc/specs/Render.