[x3d-public] [x3d] Spec Comment by on 19775-1: Abstract X3D Definitions - V3.3 [Mantis 1185]

[Roy Walmsley]

Andreas,

Many thanks for raising a specification comment on this topic. I have raised
Mantis issue 1185 to cover it, which is available to Web3D members at
http://www.web3d.org/member-only/mantis/view.php?id=1185.

There was a previous comment raised on this topic last year. It was Mantis
issue 1093 (http://www.web3d.org/member-only/mantis/view.php?id=1093). I
have added to issue 1185 that it is related to issue 1093, so that both get
considered together.

All the best,

Roy

-----Original Message-----
From: x3d [mailto:x3d-bounces at web3d.org] On Behalf Of Spec Feedback
Sent: 06 October 2017 16:51
To: x3d at web3d.org
Subject: [x3d] Spec Comment by on 19775-1: Abstract X3D Definitions - V3.3

-- Submitter indicates that this comment may be public: *Yes* --

Comment on 19775-1: Abstract X3D Definitions - V3.3
30.2.4 Sequencing Single Field (SF) events
http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components
/utils.html#SequencingEvents

-----------------
The discrete value sequencing function, f(t)

The last paragraph of section 30.2.4
(http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/component
s/utils.html#SequencingEvents)
defines the discrete value sequencing function, f(t), as

f(t) = v_n, if t_n <= t < t_{n-1}
       = v_0, if t <= t_0,
       = v_{n-1}, if t >= t_{n-1}

The are two issues:
1) in the preceding paragraphs n is used as the total number of provided
keys (and key values). However, the function uses n as an implied index.
2) the first case - when t_n <= t < t_{n-1} - can never occur since t_n is
never smaller than t_{n-1} as the keys are monotonically non-decreasing

Suggested solutions:
1) use i instead of n to indicate varying indices, following the
Interpolator function definition convention.
2) after review of current behaviour by major X3D browsers implementations
[1], the following function definition would conform to the prevalent
behaviour and remove any ambiguities:

f(t) = v_i, if t_{i} <= t < t_{i+1} for 0 <= i < n-1
       = v_0, if t < t_0,
       = v_{n-1}, if t >= t_{n-1}

[1] http://web3d.org/pipermail/x3d-public_web3d.org/2017-October/007574.html


-----------------

Submitted on Friday, 2017,  October 6 - 8:50am by  (Andreas Plesch )
IP: 140.247.105.147

See: http://www.web3d.org/node/1694/submission/1489


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