Re: [Public WebGL] Latency issues, ideas for next WebGL revision

[Thor Harald Johansen <thj@thj.no>]

> Who to bug about this... Reading through some years-old bugs: on
> Mozilla-side I guess it's Robert O'Callahan, on Webkit Oliver Hunt.
> Implementation on Linux GTK is easy (toggle a flag, add fields to
> mouse events, took me a few days on Firefox), on Mac it's supposedly
> almost as easy, on Windows you would need to go through third-party
> driver APIs, chiefly Wintab.
> https://bugs.webkit.org/show_bug.cgi?id=20458
>
> I don't know how to get more traction for this though :/

Yeah, I just want to point out some issues with Oliver Hunt's remarks on 
that bug report:

"There are multiple halfway there APIs.  The most complete is the WinTab 
API, but afaict that's not actually part of windows, but that's okay 
because it also doesn't interact with the event queue."

It doesn't need to be part of Windows any more than OpenGL needs to be. 
WinTab is pretty much the OpenGL of tablets in terms of driver support. 
Photoshop and most other applications simply look for the WINTAB32.DLL 
library and link against it. It's basically the industry standard for 
tablets.

"In all honesty I'm leaning towards supporting pressure information on 
Mac and Gtk, seriously trying to support this on windows seems to be an 
exercise in futility."

The problem he's talking about is basically that, while WinTab can 
deliver its messages to the Windows message loop (and also sports a 
polling API), these events are delivered in parallel with the system 
mouse events.

This happens because most tablet drivers will grab and control the 
Windows mouse cursor whenever the stylus is held near the tablet. I 
don't think there's room in the Windows message structure for all the 
required data. The more expensive tablets support tilt, rotation and 
other telemetry in addition the high-res position and stylus pressure.

This of course complicates matters, but it's far from being as hopeless 
as Oliver portrays it. Mouse and tablet events arrive together in the 
Windows message queue, so it's easy to just assign the data from the 
previous WT_PACKET tablet event to the current mouse event. wParam 
contains the serial number of the WinTab packet, which can be retrieved 
with WTPacket(). WinTab will then discard any prior, unretrieved packets.

Most tablets also have DPI resolutions more on par with high end 
printers than consumer monitors, and the WinTab API will provide high 
resolution data to that end. In a browser API, one could either support 
floating point mouse positions through the regular DOM fields (and break 
a lot of JavaScript code in the process) or add extra high resolution 
fields just for tablets.

Thor

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