RE: font/glyph metrics proposed wording

Sorry Lofton,
 
I meant to reply yesterday, but couldn't find the time. I thought your suggestions was a bit repetitive... I tried to make it shorter without changing the meaning.
 
[[[
For the purposes of the object extent (bounding box) calculation, each glyph is treated as a separate graphics element. The calculations assume that all glyphs occupy their full glyph cell in both the vertical and horizontal directions. Therefore, calculations assume that each glyph extends to the full ascent and descent vertical font values; and to the glyph's horizontal advance value. In CGM:1999 terminology, full ascent and descent are known as bottom-line to the top-line (see Figure 11, CGM:1999 section 6.7.3.2).  For example, the font's bottom-line and top-line typically correspond to the ymin/ymax values of the fontBBox item found in the databases of @@WebCGM's core thirteen fonts.@@  Similarly, the full horizontal extent of the glyph cell for the particular glyph -- as distinct from actual drawn extents of the glyph -- corresponds to the glyph's horizontal advancement value (WX) in the font databases of @@WebCGM's core thirteen fonts@@.
]]]



________________________________

From: public-webcgm-wg-request@w3.org [mailto:public-webcgm-wg-request@w3.org] On Behalf Of Lofton Henderson
Sent: Tuesday, April 28, 2009 7:01 PM
To: WebCGM WG
Cc: Forrest Carpenter; Robert Orosz; Ulrich Läsche
Subject: font/glyph metrics proposed wording


All --

Looking at the attached below message, we chose Option 3.  In the telecon, Benoit raised the question about horizontal extent of the text.  It is a good one, because the answer is not totally obvious when you look in the helvetica.afm file.  

We talked some more, and here is my draft of the changes to the current (15th March) editors text.  Specifically, replace the 4th paragraph of that text [1].
[1] http://www.w3.org/Graphics/WebCGM/drafts/current-editor-21/WebCGM21-DOM.html#getObjectExtent

Current 4th pgph:

[[[
For the purposes of the object extent (bounding box) calculation, each glyph is treated as a separate graphics element. The calculations assume that all glyphs occupy their full glyph cell. In particular, the calculations assume that each glyph extends vertically from the bottom-line to the top-line of the font (see Figure 11, CGM:1999 section 6.7.3.2) -- i.e., the vertical extent of each glyph includes the full ascent and descent values for the font, regardless of whether the particular glyph actually has ascenders and/or descenders.
]]]

Proposed:

[[[
For the purposes of the object extent (bounding box) calculation, each glyph is treated as a separate graphics element. The calculations assume that all glyphs occupy their full glyph cell, in both the vertical and horizontal directions. In particular, the calculations assume that each glyph extends vertically from the bottom-line to the top-line of the font (see Figure 11, CGM:1999 section 6.7.3.2) -- i.e., the vertical extent of each glyph includes the full ascent and descent values for the font, regardless of whether the particular glyph actually has ascenders and/or descenders.  The font's bottom-line and top-line (full ascent and descent values) typically correspond to font-metric information in the font database, for example the ymin/ymax values of the fontBBox item found in the databases of @@WebCGM's core thirteen fonts.@@  Similarly, the full horizontal extent of the glyph cell for the particular glyph -- as distinct from actual drawn extents of the glyph -- is typically found in the individual glyph-metric information in the font database, for example each glyph's horizontal advancement value (WX) in the font databases of @@WebCGM's core thirteen fonts@@.
]]]

I admit that the language is a little awkward in places -- I'll clean it up, or feel free to make suggestions for clean-up.

Mainly, I want WG endorsement of the basic content -- what we're saying -- and how we're presenting it ("for example").

Regards,
-Lofton.

At 05:01 PM 4/27/2009 -0600, Lofton Henderson wrote:


	Forrest has finished his action item to illustrate the font metrics:
	[1] http://lists.oasis-open.org/archives/cgmo-webcgm/200904/msg00131.html
	
	Have a look at the great picture that he generated.  
	
	This should allow the dependent tests [gOE and gOET] to go forward.  
	
	For the spec, our question is:  what changes, if any, should go into the WebCGM spec to clarify this for future implementors?
	
	Options:
	1.) none -- the existence of "FontBBox -166 -225 1000 931" in the AFM data (Helvetica in this example) should be sufficient.
	2.) normatively add to WebCGM spec the information from the AFM for the core-13 fonts of WebCGM.
	3.) in the WebCGM spec, informatively explain or add or point to the information from the AFM.
	4.) other?
	
	We will discuss on Tuesday.
	
	Note that options #2 and #3 don't answer the question for any font outside of the core-13, which can be any font that has an associated FONT PROPERTIES element.  (My opinion:  those generator/viewers need to figure out and understand what is 'bottom' and what is 'top' for the "odd" fonts, just as we have figured it out for core-13).
	
	-Lofton.
	
	

		X-Mailer: QUALCOMM Windows Eudora Version 5.1
		Date: Mon, 27 Apr 2009 16:02:18 -0600
		To: "'WebCGM'" <cgmo-webcgm@lists.oasis-open.org>
		From: Lofton Henderson <lofton@rockynet.com>
		Cc: David Cruikshank <dvdcruikshank@gmail.com>
		
		
		Forrest -- that's great!  I think your results unambiguously answer that AFM ymin is CGM:1999 'bottom' and AFM ymax is CGM:1999 'top', for all intents-and-purposes.
		
		Stuart -- you should be able to check/update your tests to ensure that you're using the right numbers for 'bottom' and 'top'.
		
		All -- we will discuss on the Tuesday vF2F agenda, what (if anything) to do about this in the WebCGM specification.  (Which has normative reference indirectly to other bits of the AFM via CGM:1999 annex I.)
		
		Regards,
		-Lofton.
		
		At 01:56 PM 4/27/2009 -0500, Forrest Carpenter wrote:
		
		

			All,
			
			 
			
			Attached are the adobe AFM file, a png image and a CGM file showing characters drawn with a cap height of 71.8 mm. The characters included are the A-ring which shows the max y of 931 and the C-cedilla which has the min y of -225. The image was generated on UNIX using the Microcosm font for Helvetica which is visually and metrically equivalent to the Adobe font. When drawn on Windows mapping Helvetica to Arial we get different results.
			
			 
			
			Regards,
			
			Forrest
			
			 
			
			 
			
			
			
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