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Re: Pointer lock spec

From: Florian Bösch <pyalot@gmail.com>
Date: Fri, 27 Feb 2015 09:22:58 +0100
Message-ID: <CAOK8ODgNO3wTPqA4Mqxuou_O35Dbw8wHbcqAHg3E1sUiorVoXg@mail.gmail.com>
To: Vincent Scheib <scheib@google.com>
Cc: Philip Jägenstedt <philipj@opera.com>, Webapps WG <public-webapps@w3.org>
I'd like to comment on the pointer lock functionality some.

12.4 notes that capturing a (a native) pointer inside of a rectangle is
difficult. I've done some research into this topic and I can attest that
it's not straightforward. Some platforms have support for this semantics,
others (I think it was OSX and Windows) would require repositioning the
pointer in an event loop which has some drawbacks.

12.5 states that there's difficulties in translation of
high-resolution/unaccelerated mouse pointer values to sensible units. While
I appreciate that concern, I don't think it matters nearly as much. The
first reason is that the user interaction with the pointing device isn't
aspect-distorted in the first place (that is a horizontal movement in the
pointing device covers the same distance on screen as a vertical movement).
What we're really discussing is mouse-sensitivity then, which could vary
greatly once mouse acceleration and sensitivity (by the OS) is taken out of
the picture. However, applications can (and will) provide their own
settings for these values. The reason to bypass acceleration/sensitivity of
the OS for a pointer is specifically because that treatment often doesn't
make sense (say for a camera control function in a 3D environment).

More general comments:

The specification does not discuss latency and pointer emulation. This is a
significant concern, as routinely native pointers have a latency of around
20-30ms, whereas the RTT for pointer-captured events and blit to display
have latencies between 70-150ms. This makes it difficult to use the pointer
lock API for emulating a mouse pointer (or indeed to use it for any kind of
pointing that requires accuracy and speed, like say FPS shooters).

A particular concern with a frequent usecase (3d interaction by mouse drag)
is the presence of pointerlock messages. Because we need native pointers
(in order to interact with DOM elements, to avoid high pointer input lag
and to allow a user to interact with things outside of the viewport (such
as tabs, file managers etc.)), it is desirable to stay out of a pointerlock
mode for general interaction. But when the application features a 3D
viewport (such as is found in CAD, 3D modelling etc.)  it is desirable to
enter pointer lock for mouse dragging in those viewports, as it avoids text
selection and screen border bump issues. A common way to do this is to
capture the mouse on mouse down, and release capture on mouse up. However,
this usecase faces some hurdles:

   1. If the user never entered pointerlock on the site, then pointerlock
   will not be entered until the user clicked "allow" in the confirmation
   dialog (this interaction is confusing to users)
   2. When he clicks allow, the mouse will be captured, but the release
   event might not have been dispatched, so that the event order suggests the
   pointer is captured, though that would run counter the semantic (I'm not
   sure what the current UA behavior there is, but this was the case in some
   UAs as of a year ago)
   3. Regardless of previous pointer capture confirmation, some UAs choose
   to display a popup with information everytime somebody enters pointerlock,
   which makes frequenty entry/exit fr

I'd also like to expand a bit on the topic of high resolution pointer
information, which means both high temporal and high spatial resolution.
For example The Razer Ouroboros mouse (
http://www.razerzone.com/gaming-mice/razer-ouroboros). It supports a
polling frequency of 1000hz and has a resolution of 8200dpi. OSes (after
they're done mangling pointers trough their machinery) clamp pointer
positions to pixels, and they clamp frequency of events at least to pixel
crossover of the pointer and to no more than 60hz or so. It would be highly
desirable to get sub-pixel accuracy of a pointing device (as is supported
by nearly all mice produced in the last 10 years) as well as higher spatial
frequency than the one imposed by the OSes pointer machinations. These
things are desirable because they allow an application that runs say a 60hz
display frequency, to temporally sub-sample a pointer location from say 16
different events. So even though at the start and end of a frame, the
pointer might be in the same position again, a movement intra-frame could
still be registered, smoothed and used. More generally this is useful to
provide a smooth feel and rapid response to applications that deal with a
need to use pointers for fast and/or accurate pointing (such as for
instance FPS shooters).

On Thu, Feb 26, 2015 at 8:21 PM, Vincent Scheib <scheib@google.com> wrote:

> Thanks, Philip, changes made.
> On Thu, Feb 26, 2015 at 10:58 AM, Philip Jägenstedt <philipj@opera.com>
> wrote:
>> Also, the EventHandler type should not be nullable, it's already
>> typedef'd to be nullable in https://html.spec.whatwg.org/#eventhandler
>> On Fri, Feb 27, 2015 at 1:56 AM, Philip Jägenstedt <philipj@opera.com>
>> wrote:
>> > https://dvcs.w3.org/hg/pointerlock/raw-file/default/index.html
>> >
>> > The section "Element Interface" should be "Extensions to the Element
>> > Interface" to match the other sections, and because it's true :)
>> >
>> > Philip
Received on Friday, 27 February 2015 08:23:26 UTC

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