This specification defines an API that provides scripted access to raw
mouse movement data while locking the target of mouse events to a single
element and removing the cursor from view. This is an essential input
mode for certain classes of applications, especially first person
perspective 3D applications and 3D modeling software.
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The Pointer Lock API provides applications the ability to directly
interpret mouse movements as an input method, rather than being limited
to only read the position of the mouse cursor. A popular example is
that of first person movement controls in three dimensional graphics
applications such as games: movement of the mouse is interpreted to
control the rotation/direction of the player's camera; no mouse cursor
is displayed, and the movement is not limited to the traditional
boundaries (such as the user agent's window, or the overall screen)
that the mouse cursor is usually subject to, meaning that any mouse
movements can be tracked indefinitely in any direction.
Pointer Lock is related to Mouse Capture [MSDN-SETCAPTURE]
[MDN-SETCAPTURE] (Mouse Capture is unspecified: bug 14600).
Capture provides continued event delivery to a target element while a
mouse is being dragged, but ceases when the mouse button is released.
Pointer Lock differs by being persistent, not limited by screen
boundaries, sending events regardless of mouse button state, hiding the
cursor, and not releasing until an API call or specific default
unlock gesture by the user.
Pointer Lock deals with capturing a single resource and relating it to
a single element. This is similar to the Fullscreen API [FULLSCREEN],
which promotes a single element to be full screen. The Pointer Lock API
chooses to pattern the resource capture, state change, and release API
as closely as possible after the Fullscreen API.
The Pointer Lock interaction mode was previously referred to as mouse
lock. The name was changed as many different controller types besides
mice can manipulate the on screen pointing cursor, and they are all
impacted.
2.
Glossary
Engagement gesture
An event generated by the user agent as a result of user interaction
processed by the user agent to interact with the page. e.g.
click, but not mousemove. Engagement
gestures are any events included in the definition of being
triggered by user activation with the addition of
keypress and keyup. Note that operating
system level accessibility and internationalization features may
intercept gestures before the user agent processes them for
interaction with a page. E.g. multiple key press codes used to enter
an extended international character.
3.
pointerlockchange and pointerlockerror Events
Two events are used to communicate pointer lock state change or an
error in changing state. They are named pointerlockchange
and pointerlockerror. If pointer lock is entered or exited
for any reason a pointerlockchange event must be sent.
Magnification software increases the size of content on the screen. It
uses the mouse to move the magnified point of focus around. When a
pointer lock is initiated, the magnification software needs to switch
to using the keyboard to move the magnified point of focus around
instead. When a pointerlockchange event is fired, web browsers
therefore need to make sure the event is communicated to assistive
technologies like screen magnifiers.
4.
Extensions to the Element Interface
The Element interface is extended to provide the ability to
request the the pointer be locked.
Requests that the pointer be locked to a DOM element
target. The user agent determines if pointer lock
state will be entered and upon lock state change or error must send
either a pointerlockchange or pointerlockerror event
respectively.
If a user has exited pointer lock via the default unlock
gesture, or pointer lock has not previously been entered for
this document, an event generated as a result of an engagement
gesture must be received by the document before
requestPointerLock() will succeed.
Once in the locked state the user agent must fire all
relevant user generated MouseEvent events (for example:
mousemove, mousedown, mouseup, click, and wheel)
[ui-events] to the target of pointer lock, and not fire
mouse events to other elements. Events that require the concept of
a mouse cursor must not be dispatched (for example: mouseover,
mouseout, drag, and drop).
In the locked state the system mouse cursor must be hidden.
Movement and button presses of the mouse must not cause the window
to lose focus.
Synthetic mouse events created by application script act the same
regardless of lock state.
Initiates an exit from pointer lock state if currently locked to a
target whose shadow-including root is this document, and
sends a pointerlockchange event when the lock state has been
exited.
The system mouse cursor must be displayed again and positioned at
the same location that it was when pointer lock was entered (the
same location that is reported in screenX,
screenY, when the pointer is locked).
While the pointer is locked, returns the result of
retargeting the element, which is the target for mouse
events, against the context object if the result and the
context object are in the same tree, otherwise returns null.
Returns null if lock is pending or if pointer is unlocked.
Note: the example uses fictional shadow-root element
to denote a shadow root instance.
If #canvas1 is the target,
document.pointerLockElement returns
#host1, and root1.pointerLockElement
returns #canvas1. The result of retargeting#canvas1 against #root2 is
#host1, but as #host1 is not in the same
tree as #root2, null will be returned for
root2.pointerLockElement.
The attributes movementXmovementY must provide the change
in position of the pointer, as if the values of
screenX, screenY, were stored between two
subsequent mousemove events eNow and
ePrevious and the difference taken movementX =
eNow.screenX-ePrevious.screenX.
movementX/movementY must be zero for all mouse events
except mousemove. All motion data must be delivered
via mousemove events such that between any two mouse
events earlierEvent and currentEvent the
value of currentEvent.screenX-earlierEvent.screenX is
equivalent to the sum of all movementXmovementY/code>
events after earlierEvent, with the exception of when
screenX can not be updated because the pointer is clipped by the
user agent screen boundaries.
When unlocked, the system cursor can exit and re-enter the user
agent window. If it does so and the user agent was not
the target of operating system mouse move events then the most
recent pointer position will be unknown to the user agent
and movementX/movementY can not be computed and must be set
to zero.
When pointer lock is enabled clientX,
clientY, screenX, and
screenY must hold constant values as if the pointer
did not move at all once pointer lock was entered. But
movementX/movementY must continue to provide the change in
position of the pointer as when the pointer is unlocked. There will
be no limit to movementX/movementY values if the mouse is
continuously moved in a single direction. The concept of the mouse
cursor will have been removed, and it will not move off the window
or be clamped by a screen edge.
Large movement values must not appear in situations when mouse
input is interupted, such as the mouse cursor leaving the window
and then re-entering at another location. If a User agent
experiences a gap in receiving mouse input data from the operating
system then the next generated mousemove event must
have movementX/movementY set to 0. These gaps
may appear for example when the User agent receives a mouse
leaving event at the window system API. As an exception mouse
capture may allow the User agent to continue receiving mouse
events when the cursor moves outside the window.
A default unlock gesture must always be available that will
exit pointer lock.
Note
Pointer lock must be exited if the targetbecomes disconnected, or the user
agent, window, or tab loses focus. Moving focus between elements of
active documents, including between browsing
contexts , does not exit pointer lock. E.g. using the keyboard to
move focus between contents of frames or iframes will not exit.
Pointer lock must not be exited when fullscreen [FULLSCREEN] is
entered or exited unless the pointer is required to enable interaction
with the user agent graphical user interface, the default
unlock gesture was used to exit both fullscreen and pointer lock,
or window or tab focus was lost.
10.
Use Cases
This section is non-normative.
10.1
Relative view-port rotation of free moving virtual actors
A player on a first/third person game will need to control the
view-port orientation. A widely used method is the use of mouse
movements to control the viewing angle. This kind of application can
use the Pointer Lock API to allow a complete freedom of control over
the viewport's yaw and pitch even when the user is not pressing mouse
buttons. Those buttons can be used for other actions while constantly
providing navigation via mouse movement.
10.2
Free rotation of 3D models or panning of 2D layers
Users of a three dimensional modeling application will need to rotate
models. A application can use the Pointer Lock API to enable the
author to rotate the model freely in a drag operation without
limiting motion. Without pointer lock a drag would stop providing
motion data when the mouse cursor is limited by the edge of the
screen.
Similarly, absolute motion panning of a large two dimensional image
could be permitted in a single drag operation without cursor / screen
limits.
10.3
Relative movement of actors
A player on a fast reflexes game controls a paddle to bounce back a
ball to the opponent, while allowing the same paddle to execute
actions based on different mouse buttons being pressed. The
application can use the Pointer Lock API to allow the player to react
quickly without being concerned about the mouse cursor leaving the
game play area and clicking another system application, thus breaking
the game flow.
10.4
Jog movement over spinner controls
When modifying numerically magnitudes in applications sometimes the
user will prefer to "drag" a numeric control by its button handles to
increment or decrement the numeric value. E.g. a spinner with a
number entry text box and arrows pointing up and down that can be
clicked or dragged on to change the value. An application could use
the Pointer Lock API to allow modifying the numeric values beyond
what the logical screen bounds allow. The same could apply for a
control that fast forwards or rewinds a video or audio stream like a
"jog".
10.5
Synthetic cursor interaction with HTML DOM UI
Some games use a classical cursor, however they want it to be limited
or controlled in some manner. E.g. limited to the bounds of the game,
or movable by the game. Locking the pointer enables this if the
application creates their own cursor. However HTML and DOM should
still be available to use for user interface. Synthetic mouse events
should be permitted to allow an application defined cursor to
interact with DOM. E.g. the following code should permit a custom
cursor to send click events while the pointer is locked:
document.addEventListener("click", function (e) {
if (e._isSynthetic)
return;
// send a synthetic clickvar ee = document.createEvent("MouseEvents");
ee._isSynthetic = true;
x = myCursor.x;
y = myCursor.y;
ee.initMouseEvent("click", true, true, null, 1,
x + e.screenX - e.clientX,
y + e.screenY - e.clientY,
x,
y);
var target = document.elementFromPoint(x, y);
if (target)
target.dispatchEvent(ee);
});
Note that synthetic clicks may not be permitted by a user
agent to produce the same default action as a non-synthetic
click. However, application handlers can still take action and
provide user interface with existing HTML & DOM mechanisms.
10.6
View-port panning by moving a mouse cursor against the bounds of a
view-port.
Real Time Strategy games often use this technique. When the player
moves the pointer to the view-port borders, if they "push" the border
with a mouse movement, the view-port is panned over the game area
according to how much they move the mouse. When moving the mouse
cursor within the bounds of the view port it acts at is typically
would on a system. Applications may choose to implement this using
pointer lock and the previous use case of "Synthetic cursor
interaction with HTML DOM UI" to bring cursor behavior completely
under their control.
10.7
Game Lobby, timer based pointer lock
Games that use pointer lock may desire a traditional UI and system
cursor while players prepare in a game lobby. Games usually start
after a short timer when all players are ready. Ideally the game
could then switch to pointer lock mode without requiring an
engagement gesture. Players should be able to seamlessly move
from the game lobby into game navigation.
10.8
Game Portal
Game portals, and other sites such as Facebook and Google Plus, host
games for users to play. These games may be hosted and served from a
different origin from that of the portal site. Embedded games should
be able to lock the pointer, even in non-full screen mode.
11.
Security
This section is non-normative.
Security Concerns:
User actions may be misdirected to elements the user did not intend
to interact with.
Pointer Lock will remove the ability of a user to interact with
user agent and operating system controls
Pointer Lock can be called repeated by script after user exits
pointer lock, blocking user from meaningful progress.
Full screen exit instructions are displayed in some user
agents when the pointer is moved to the top of the screen. During
pointer lock that gesture is not possible.
Responses:
User agents may limit what security origins may lock the
pointer.
User agents may prompt for confirmation before locking, this
preference may be saved as a content setting.
Persistent display of escape instructions can be provided.
Repeated escapes of pointer lock can signal user agent to
not re-lock the pointer without more specific engagement
gesture, e.g. similar to how Chrome suppresses repeated alert()
calls.
Changing to new tabs, windows, or any other action that causes a
page to lose focus will exit pointer lock.
Pointer lock can only be engaged when the window is in focus in the
user agent and operating system.
Recommendations:
Esc key should exit pointer lock.
Preferences per sub-domain can be used to allow or block pointer
lock, similar to pop-up, geolocation, and fullscreen.
Pointer lock is a required user interaction mode for certain
application types, but carries a usability concern if maliciously used.
An attacker could remove the ability for a user to control their mouse
cursor on their system. User agents will prevent this by always
providing a mechanism to exit pointer lock, by informing the user of
how, and by limiting how pointer lock can be entered.
User agents will determine their own appropriate policies, which
may be specialized per device or differ based on user options.
12.
Frequently Asked Questions
This section is non-normative.
12.1
Why not merge with Mouse Capture: setCapture()?
Mouse Capture [MDN-SETCAPTURE] handles low security risk mouse
event target lock for the duration of a mouse drag gesture. Pointer
lock removes the concept of the cursor and directs all events to a
given target. They are related, but different.
If a browser implemented both, it would be reasonable to support a
combination of traits: The security simplicity of "automatically
release lock when mouse up" and the increased functionality of total
control over mouse input and removal of the system cursor. The
security trait would allow more permissive use of the feature for
applications that only required a short burst of pointer lock during
a drag event.
This functionality is omitted from the initial version of this spec
because it helps the minor use cases in windowed mode but we still do
not have an implementation solving the major ones. And, to implement
this a browser must implement both, which none does yet. It is not
clear if this feature should live on .lock or on .setCapture. If both
were implemented, either API could be augmented fairly easily to
offer the hybrid functionality.
12.2
Why not repurpose MouseEvent's .clientX/Y .screenX/Y?
Even in non locked state, the delta values of mouse movement are
useful. Changing the meaning of .client or .screen based on lock
state would also cause easy errors in code not carefully monitoring
the lock state.
12.3
Why use .movementX/Y instead of .deltaX/Y?
When the pointer is locked 'wheel' events should be sent to the
pointer lock target element just as 'mousemove' events are.
There is a naming conflict with .deltaX/Y/Z as defined in
DOM 3 'wheel' event.
12.4
Why bundle all functionality (hiding cursor, providing mouse deltas)
instead of using CSS to hide the cursor, always providing delta
values, and offering an API to restrict the cursor movement to a
portion of the web page?
There are good motivations to provide a more fine grained approach.
E.g. the use case "View-port panning by moving a mouse cursor against
the bounds of a view-port" doesn't require hiding the mouse cursor,
only bounding it and always having delta values available. Also, this
specification defines the movement deltas to be taken from how the
system mouse cursor moves, which incorporates operating system
filtering and acceleration of the mouse movement data. Applications
may desire access to a more raw form of movement data prior to
adjustments appropriate for a mouse cursor. Also, raw data may
provide better than pixel level accuracy for movement, as well as
higher frequency updates. Providing the raw delta movement would also
not require special permission or mode from a user, and for some set
of applications that do not require bounding the cursor may reduce
the security barriers and prompts needed.
There are two justifications for postponing this finer grained
approach. The first is a concern of specifying what units mouse
movement data are provided in. This specification defines
.movementX/Y precisely as the same values that could be recorded when
the mouse is not under lock by changes in .screenX/Y. Implementations
across multiple user agents and operating systems will easily
be able to meet that requirement and provide application developers
and users with a consistent experience. Further, users are expected
to have already configured the full system of hardware input and
operating system options resulting in a comfortable control the
system mouse cursor. By specifying .movementX/Y in the same units
mouse lock API applications will be instantly usable to all users
because they have already settled their preferences.
Secondly, the implementation of providing movement data and bounding
the mouse cursor is more difficult in the fine grained approach.
Bundling the features together gives implementations freedom to use a
variety of techniques as appropriate on each operating system and is
more practical to implement. Direct APIs do not exist on major
desktop platforms (Windows, Mac OS X, Linux) to bound the cursor to a
specific rectangle, and prototypes have not yet been developed to
demonstrate building that behavior by e.g. invisible
windows with Xlib
or manual cursor movement on Mac. Unaccelerated Delta values have
been proposed to be accessed by reading raw Human Interface Device
(HID) data. E.g. WM_INPUT messages on Windows, and USB device APIs on
Mac OS X / Linux. The challenge here is interpreting and normalizing
the units to some consistent and specifiable scale. Also, most APIs
considered to date are limited to USB devices.
It would be reasonable to consider adding these capabilities in the
future, as the currently specified pointer lock API would be easy to
continue to support if the finer grained delta and confinement
features were implemented.
The bundled API is selected for implementation practicality, because
the desired use cases are supported, and because it will not conflict
with future improvements as discussed here.
12.5
High resolution deltas / High frequency updates?
12.6
Why modify MouseEvent and reuse existing mouse events instead of
creating a mouse delta event?
When under pointer lock many mouse events remain relevant, e.g.
click, mousedown, etc. These all share the same event data structure
MouseEvent. If movement data were reported via a new data structure
then a new event would be needed for reporting delta movement. The
new data structure would have many parallels to MouseEvent to offer
the same conveniences, e.g. button and modifier key states. When
handling click, down, and up events would the existing mousedown,
mouseup be used? If so, they would provide .clientX/Y and .screenX/Y
with no useful data, but would lack the convenience of containing the
current movement data. Or, new events would also be required for when
the mouse is locked.
Also, movementX/Y are convenient even when the mouse is not locked.
This spec requires movement members to always be valid, even when the
mouse cursor exists. This reduces code required to track the last
cursor state and mouseover/mouseout transitions if applications wish
to make use of delta motion of the mouse.
The only negative of adding movementX/Y to MouseEvent appears to be
the unused values in clientX/Y and screenX/Y when under pointer lock.
This does not seem to be a significant problem.
Therefore the minimal change to add movementX/Y to MouseEvent is
selected to reduce API and implementation complexity.
12.7
Why separate targets for mouse events under pointer lock and keyboard
input focus?
Consider a game with a 3D view controlled by moving the mouse cursor,
while the user may still chat with other users via a text console. It
is reasonable for the application to accept text input to an element
that is different than where mouse events are being dispatched. This
is similar to pre-existing behavior of receiving mousemove events
over any element while typing into a form on a page.
13. Conformance
As well as sections marked as non-normative, all authoring guidelines,
diagrams, examples, and notes in this specification are non-normative.
Everything else in this specification is normative.
This specification defines conformance criteria that apply to a single
product: the user agent that implements the interfaces that
it contains.
A.
Acknowledgments
This section is non-normative.
Many thanks to lots of people who made contributions to the discussions of this specification: