[x3d-public] SFImage regex

[Andreas Plesch]

Two more observations which may be worth while being stated explicitly:

The regexes are expected to be used just against attribute strings, not the
complete element xml, or scene xml . I think that is implied by how XML
native data types are referenced.
Partial matches do not count as successful. That means, there needs to be
an additional check if the matched portion of the string is identical to
the string. I think that is implied how the existing regexes are formulated.

And two more question:

The existing regexes do not allow for leading white space. It looks like
this is inspired by XML spec. regexes:
https://www.w3.org/TR/xmlschema11-2/#decimal . However, native XML decimal
integers and floats allow leading white space due to the fixed  whiteSpace:
collapse restriction.
Should therefore optional leading white space be added to the existing
regexes ? I think so, or alternatively removed from native using types (by
not using native types).
For SF fields which contain multiple numbers, such as SFVec or SFColor, the
existing regexes require exactly one space character as separator. What is
the rationale for not allowing repeated space characters which may help
with formatting ?

-Andreas

On Thu, Jun 7, 2018 at 2:11 PM Andreas Plesch <andreasplesch at gmail.com>
wrote:

> Since I got started with the regexes, let's look at SFImage as it is still
> a TODO.
>
>
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/fieldsDef.html#SFImageAndMFImage
>
> appears to be the main (only?) source of the format description.
>
> We need exactly three decimal non-negative integers followed by a zero or
> more non-negative decimal or hexadecimal integers.
>
> There is no mentioning of the separator, so let's look at some example
> scenes:
>
>
> http://www.web3d.org/x3d/content/examples/ConformanceNist/Appearance/PixelTexture/index.html
>
> The NIST examples all use space as separator.
> http://www.web3d.org/x3d/tooltips/X3dTooltips.html#PixelTexture examples
> all use space.
>
>
> http://www.web3d.org/specifications/X3dSchemaDocumentation4.0/x3d-4.0_SFImage.html
> has a minimum length of 5, presumably as a result of three single digits
> for wdth, height and components plus two separator characters.
>
> So one question is: Are single commas legal to separate numbers in SFImage
> from each other ?
> http://www.web3d.org/specifications/X3dRegularExpressions.html says
> commas are only allowed in MF fields, so let's say the answer is no.
>
> What about leading zeroes ? The general guidance in
> http://www.web3d.org/specifications/X3dRegularExpressions.html does not
> allow leading zeroes.
>
> There is a requirement to have width x height x component number of pixel
> values but I am not sure if this requirement can be (easily) checked by a
> regex.
>
> Capital letters:
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/fieldsDef.html#SFImageAndMFImage
> only uses capital A-F in hexadecimal example values but let's say a-f is
> also allowed since they are used in almost all examples.
>
> Ok, let's give it a try:
>
> [ \t]*(([0-9]|[1-9][0-9]+)([
> ]+|$)){3}(([0-9]|([1-9][0-9]+)|(0x([0-9]|[a-f]|[A-F])+))([ ]+|$))*
>
> In words:
>
> match any leading white space followed by
> exactly three times the following
>  - one of the following
>    - either a single digit (including 0) or
>    - a two or more digit number starting with a 1 to 9 digit
>  - followed by either
>   - one or more spaces
>   - or the end of the string (accommodating the default '0 0 0' case)
> then optionally followed zero or more times by
>   - one of the following
>     - either a single digit (including 0) or
>     - a two or more digit number starting with a 1 to 9 digit
>     - 0x followed by at least one of
>        - a single digit or
>        - a to f letter or
>        - A to F letter
>   - followed by either
>     - one or more spaces
>     - or the end of the string
>
> The spaces are written as [ ] for clarity but could be just a space
> character.
>
> This allows 0 0 0 as it is the default value. It also allows 1 2 3 without
> any pixel values.but we do not aim at checking the number of pixel values
> anyways.
>
> Any input, in particular examples of problem cases welcome. Since images
> can be huge it may be necessary to optimize for performance and memory
> which may require more regex expertise than I can bring myself to acquire.
>
> -Andreas
>
> --
> Andreas Plesch
> Waltham, MA 02453
>


-- 
Andreas Plesch
Waltham, MA 02453
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