RE: [cgmo-webcgm] more getObjectExtent questions

[Lofton Henderson <lofton@rockynet.com>]

Answering Dieter & Dave together:

At 12:16 PM 6/13/2008 -0400, Weidenbrueck, Dieter wrote:
> re
> Question 2:
> Both size and style
> properties should affect the box. If transform as a transient state
> affects the box, so should style
> properties.

Good point, I agree.

At 09:41 AM 6/13/2008 -0700, Cruikshank, David W 
wrote:
> Question
> 1: Agree to Lofton's recommendataion

Okay, I'm going to fix that wording now.

>  
> Question 2: I think
> text-size is the only SP (other than transform) that has an effect on
> gOE().

I think text-font would affect it also.  Every font has its own
vertical font metrics, which determines the exact BL-to-TL number, 
when for example RTT is boxed-cap (and accordingly you are fitting the
fonts baseline-to-capline metric to the RT box height.)

-Lofto

---

From: Lofton Henderson [mailto:lofton@rockynet.com]
Sent: Freitag, 13. Juni 2008 17:53
To: cgmo-webcgm@lists.oasis-open.org
Subject: [cgmo-webcgm] more getObjectExtent questions

All --

I don't have enough detail to finish the editing for text size and getObjectExtent.  The minutes said:  "Approved: wording of bottom line to top line and length of the restricted text box or the sum of width metrics for the text string in the case of a substring"

The current text in 5.7.6 for gOE() reads:  "The bounding box calculation is based on the abstract locus of the primitives within the APS. It is not affected by CGM Primitive Attribute (such as line width) or Control elements, nor by APS Attributes or Style Properties. It is affected by geometric transform. "

From previous discussion, I think concluded that we do want the size of the text to affect the extent.  Correct?  So we probably want to modify the current wording at least for "...except size of text, which affects the box as follows..."  Which leads to the first question.

QUESTION 1:  How should size of text affect getObjectExtent?

Discussion:  The telecon-resolved "bottom line to top line" is fine in general.  But it leaves some detail unanswered:  BL-to-TL of what?  I think we want:  BL-to-TL of the font size that is actually used to render the Restricted Text, after taking into account all text attributes, the Restricted Text box height (rt-height), the Restricted Text Type (RTT), etc.

About the latter ... does RTT affect it?  The stated motivation for BL-to-TL is to accommodate possible diacritical marks and descenders without having to do character-by-character analysis of the string.  So if RTT were boxed-cap, then the contribution of a text element to gOE would be a little bigger than the rt-height.  If the RTT were boxed-all, then the rt-height itself equals the needed BL-to-TL distance.

Recommendation:  The gOE() extent calculation should use the BL-to-TL of the effective font size that reflects all text attributes, the height (rt-height) of the Restricted Text box, and the Restricted Text Type.

Note that these are still easy computations compared to stroke-by-stroke.  Just more fully specified.  Some wording like the above paragraph would go into gOE().

QUESTION 2:  Should the text-size and font Style Properties affect getObjectExtent()?

Discussion:  Should the text-size Style Property have an effect?  I.e., should the gOE() reflect the original WebCGM contents, or the transiently modified viewed version?

My initial inclination is "no".  But I don't feel strongly and could easily be convinced otherwise.  I base "no" on the principle that text-size (and text-font) SP are transient visual changes whose main use case is to produce a highlighting or attention-getting effect. 

If you think that the use case for this stuff requires "yes" -- i.e. text related SP do affect gOE() -- please comment.

Recommendation (weak preference):  text-related SP do not affect it. 

Conclusion:  I don't think the particular resolutions are critical.  We just need a little more detail so that implementors and users have uniform expectations.

-Lofton.

[1] http://docs.oasis-open.org/webcgm/v2.1/cd01/WebCGM21-DOM.html#L5095
[2]
At 03:56 PM 6/11/2008 +0000, david.w.cruikshank@boeing.com wrote:

[...] http://www.oasis-open.org/apps/org/workgroup/cgmo-webcgm/download.php/28529/20080611_WebCGM_TC_Telecon_minutes.pdf PLEASE NOTE:  If the above links do not work for you, your email application may be breaking the link into two pieces.  You may be able to copy and paste the entire link address into the address field of your web browser. -OASIS Open Administration