[x3d-public] X3D VR

[Andreas Plesch]

Hi,

back from the holiday season, here are proposals for new fields for
Viewpoint.

I do not have an x3dom implementation but the idea is to add two Matrix4d
fields:

projectionMatrix :

default: NULL

purpose: allow control of the view projection from 3d to 2d by such a
matrix from sources such HMD drivers. The projection matrix controls fov

The projectionMatrix should be used as is by the browser if not NULL. If
NULL, a projection matrix shall be contructed from viewpoint fields.

viewMatrix:

default: unit matrix

purpose: allow control of the viewer orientation and location by such a
matrix from sources such as HMD drivers.

The viewMatrix V shall be combined with the matrix M derived from the
location/ orientation fields by M * V for rendering use.

This means that if V is used in a scene exclusively the location fields
needs to be reset to 0 0 0 from its default by the scene.
Typical use would be as sinks of routes from (new) ProjectionSensor or
VRDevice node fields.

A VRDevice delivers both matrixes for each eye. A scene can then set up a
viewpoint for each eye, and use Layers to show them side by side.

In terms of efficiency, this would seem to require repeated traversals of
the scene unless both Layers can be recognized to show the same scene
content.

A more convenient and integrated alternative would be to introduce a stereo
SFBool field and have left and right variants of the matrix fields ( and
perhaps also left and right variants of the location, orientation, fov,
zfar, znear fields).

stereo = false would ignore all left and right fields.
stereo = true would use the left/right fields and render them side by side.

Since in this case there is a guaranty that views for each eye use the same
scene content, only one traversal should be needed to render both eyes.

The idea would be switching mono to stereo and back only requires toggling
the stereo field. Navigation may have a similar switch to and from
mouse/keyboard modes ?

Implementation in x3dom of viewMatrix and projectionMatrix may be rather
straightforward. I do not see large obstacles (famous last words ...).
Implementation in cobweb of viewMatrix and projectionMatrix may be also
straightforward but I am less sure.

Without layers in x3dom then one could put two scene side by side on the
web page, use external js to feed the matrix fields, and then also use
external js to grab the frames from both scene canvases, combine them into
a single frame on another canvas, and use that finally as a source for the
HMD display. (This sounds slow).
In cobweb, it should not be hard to set up a scene with a layer for each
eye.

Implementation of stereo, left and rightView/ProjectionMatrix in x3dom is
harder since it needs changes to the rendering code which is a bit
unstructured. The first approach would be for stereo=true to go through the
rendering twice with the rendering surfaces appropriately set somehow.

-Andreas

On Dec 21, 2016 6:00 AM, "Roy Walmsley" <roy.walmsley at ntlworld.com> wrote:

Hi Andreas,



That’s great to see what you have been doing here. Would  you like to take
your node suggestions one step further and propose the fields that might be
specified for each node?



What we could do then is, in the new year, is to host an open discussion on
WebVR and X3D. Contributions from any other readers are welcome, and could
lead to a lively discussion on this topic.



Thank you for the suggestions,



All the best,



Roy



*From:* x3d-public [mailto:x3d-public-bounces at web3d.org] *On Behalf Of *Andreas
Plesch
*Sent:* 21 December 2016 05:51
*To:* X3D Graphics public mailing list <x3d-public at web3d.org>
*Subject:* [x3d-public] X3D VR



Hi

Working with x3dom and WebVR I am exploring what additions to X3D would be
necessary or useful to effectively use current VR hardware such as the
Rift, Vive, Gear, or Cardboard.

The proposed RenderedTexture node is currently used in x3dom with special
stereo modes to generate left and right views from a single viewpoint in a
single GL context.

A Layer for each left and right view could also be used with two
coordinated but separate viewpoints. This would be Cobweb's pattern.

Since the HMD and its own runtime know best the internal optical
characteristics of the display, the preferred interface at least in WebVR
are view and projection matrixes directly usable by consumers for 3d
graphics generation, and not position, orientation and fov. This leads to a
new requirement for X3D to accept these raw matrixes as input.

Since x3dom uses RenderedTexture for VR, I added there additional special
stereo modes which directly receive these matrixes from the HMD to be used
for rendering at each frame. This in effect accomplishes a first, head and
body based, level of navigation. In my first tests (on github) it works
well and should be robust across devices. This approach does require some
standard API to the HMD such as WebVR.

Another possibility is to add view and projection matrix fields input
fields to viewpoints which can be continually updated. One could convolve
the view matrix with position/orientation fields, or optionally completely
ignore them.

One then could use external SAI to keep updating or perhaps introduce an
environment ProjectionSensor. It would relay these matrix events from an
HMD runtime to then be routed to the viewpoints.

A second level of navigation is accomplished with handheld controllers.
Until some standard gestures evolve, it will be necessary to expect custom
per scene navigation. X3d should have a way to sense buttons and axes
velocities of such controllers so these are then available to manipulate
the view in some way. InstantReality has a general IOSensor to that effect.
On the web the GamePad API is a standard which would need to be used.

Summary: RenderedTexture with stereo modes, matrix fields for viewpoints, a
ProjectionSensor, and a ControllerSensor would all be candidates for x3d VR
support.

Thanks for reading, any thoughts welcome,

Andreas
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