Re: [oslc-core] Issue: Relative Length Units

[Steve K Speicher <sspeiche@us.ibm.com>]

I think either way though, Martin's reference
to is saying that px is relative to the device.  The device is constant
between the two though, where the others (em) are based on their own content
(font type and size).  So with either definition seems like px would
be the best way for them to both be "talking the same units",
be a bit more precise.

Thanks,
Steve Speicher
IBM Rational Software
OSLC - Lifecycle integration inspired by the web -> http://open-services.net



From:      
 Samuel Padgett/Durham/IBM@IBMUS
To:      
 Martin P Pain <martinpain@uk.ibm.com>
Cc:      
 "OASIS OSLC Core
TC Discussion List" <oslc-core@lists.oasis-open.org>
Date:      
 05/30/2014 08:54 AM
Subject:    
   Re: [oslc-core]
Issue: Relative Length Units
Sent by:    
   <oslc-core@lists.oasis-open.org>

---

Interesting. I was looking at

http://www.w3.org/TR/CSS2/syndata.html#length-units

which calls out only em and ex. It lists px as an absolute unit.

The OSLC spec actually has the same link as you, but it seems to be an
earlier draft (candidate recommendation vs recommendation).

-- 
Samuel Padgett | IBM Rational | spadgett@us.ibm.com
Eclipse Lyo: Enabling tool integration with OSLC

Martin
P Pain ---05/30/2014 04:54:23 AM---In CSS terms, pixel values are relative
units. The link in the text you  copied [1] states:

From:	Martin P Pain <martinpain@uk.ibm.com>
To:	Samuel Padgett/Durham/IBM@IBMUS
Cc:	"OASIS OSLC Core TC Discussion List" <oslc-core@lists.oasis-open.org>
Date:	05/30/2014 04:54 AM
Subject:	Re: [oslc-core] Issue: Relative Length Units

---

In CSS terms, pixel values are relative units. The link in the text
you copied [1] states: 

"Relative units are:

• em: the 'font-size' of the relevant font
• ex: the 'x-height' of the relevant font
• px: pixels, relative to the viewing device

...Pixel units are relative to the resolution of the
viewing device, i.e., most often a computer display. If the pixel density
of the output device is very different from that of a typical computer
display, the user agent should rescale pixel values. ... It is recommended
that the reference pixel be the visual angle of one pixel on a device
with a pixel density of 96dpi and a distance from the reader of an arm's
length." 

I don't know if anything calculates reference pixel values like that, but
by the wording of our spec and the CSS spec pixel values are allowed for
the height and width values of previews and dialogs.

However your comment does appear to be correct, about the reference to
"default system font (at 100% size)" being incorrect.

[1] http://www.w3.org/TR/2009/CR-CSS2-20090423/syndata.html#length-units

Martin Pain
Software Developer - Green Hat
Rational Test Virtualization Server, Rational Test Control Panel
OASIS Open Services for Lifecycle Collaboration - Automation technical
committee chair

E-mail: martinpain@uk.ibm.com Find me on:  and within IBM on:

IBM United Kingdom Limited
Registered in England and Wales with number 741598
Registered office: PO Box 41, North Harbour, Portsmouth, Hants. PO6 3AU

<oslc-core@lists.oasis-open.org> wrote on 29/05/2014 19:35:40:

> From: Samuel Padgett <spadgett@us.ibm.com>
> To: "OASIS OSLC Core TC Discussion List" <oslc-core@lists.oasis-open.org>,
> Date: 29/05/2014 19:35 
> Subject: [oslc-core] Issue: Relative Length Units
> Sent by: <oslc-core@lists.oasis-open.org>
> 
> I have some doubts about our use of relative length units for 
> delegated UIs in OSLC.
> 
> In OSLC 2.0, widths and heights for dialogs and resource previews
> must always use relative length units [1] [2] [3]. We make the 
> additional statement that em and ex units are relative to the 
> default system font. For instance,
> 
> "Height size MUST be expressed in relative length units as defined
in the 
> W3C Cascading Style Sheets Specification (CSS 2.1) Em and ex units
> are interpreted relative to the default system font (at 100% size)"
> 
> The second sentence to me seems to contradict the first. In CSS, em
> is calculated relative to the font size of the parent element, not
> the system font. As a dialog consumer, how do I adjust for the difference?
> 
> The other issue I see is that I can't accurately size myself as a
> dialog since I have no idea what font size is used on the emedding
> (outer) page. If the outer page uses a larger font than me, my 
> dialog will be bigger than I want. If the outer page uses a smaller
> font, the dialog will be smaller than I want. It's not based on my
> content and font, but the font of the outer page.
> 
> The real OSLC implementations I've seen just ignore all this and use
> px values. I did some searching and couldn't find any history for
> why we require relative units.
> 
> I propose we remove the requirement and simply say use any valid CSS
> length value.
> 
> [1] http://open-services.net/bin/view/Main/OslcCoreUiPreview?
> sortcol=table;up=#Resource_Preview
> [2] http://open-services.net/bin/view/Main/OslcCoreSpecification?
> sortcol=table;up=#Resource_Dialog
> [3] http://open-services.net/bin/view/Main/OslcCoreSpecification?
> sortcol=table;table=up#Dialog_Resizing
> 
> -- 
> Samuel Padgett | IBM Rational | spadgett@us.ibm.com
> Eclipse Lyo: Enabling tool integration with OSLC
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