MarkToBase clarification?

[Ken Lunde]

Thank you, Kamal. Tsuda-san sends his thanks for this meaningful reply, which I forwarded to him.

-- Ken

> On Feb 5, 2018, at 12:17 PM, Mansour, Kamal <Kamal.Mansour at monotype.com> wrote:
> 
> Ken,
> 
> In reply to your friend at Fontworks, I would first say that I don't think he has a language problem in this case.
> 
> As far as I know, there are two types of attachment points: one has the same meaning as "anchor point", while the other refers to inter-character linking in cursive scripts. 
> 
> In the case of mark-to-base lookups, the base acts as the carrier, while the mark is always positioned relative to it. For a combination such as â, a is the base (carrier) while ˆ (circumflex) is the mark. Typically, a carries an anchor point above its body which needs to be aligned with an anchor on the circumflex. To get the correct visual results, the position of the anchor on the a, as well as the position of a on the line, are combined to get "the final pen point", after which the anchor point of the circumflex is aligned to match the anchor of the a.
> 
> Kamal
> 
> From: mpeg-OTspec at yahoogroups.com <mpeg-OTspec at yahoogroups.com> on behalf of Ken Lunde lunde at adobe.com [mpeg-OTspec] <mpeg-OTspec-noreply at yahoogroups.com>
> Sent: Monday, February 5, 2018 10:31:44 AM
> To: mpeg-OTspec at yahoogroups.com
> Subject: [mpeg-OTspec] MarkToBase clarification?
>  
> All,
> 
> For those who are familiar with MarkToBase, the following was sent to me from a friend at Fontworks, a type foundry in Japan:
> 
> > Could I ask you a question about the MarkToBase in the GPOS table in the OpenType spec?
> > It says:
> > 
> > "To combine the mark and base glyph, the client aligns their attachment points, positioning the mark with respect to the final pen point (advance) position of the base glyph."
> > 
> > The above is the first sentence where "attachment points" appear in the LookupType 4.
> > I think the points are used for the same meaning as anchor points in the context. Am I correct?
> > If so, why are these two points used separately here?
> > 
> > Moreover I have been having a hard time understanding the "positioning the mark with respect to the final pen point (advance) position of the base glyph" part.
> > It says "the client aligns their attachment points" and that means the mark has been already positioned but why does it say ",positioning the mark ...base glyph" again?
> > 
> > Because I am a non-native English speaker, it may be over my head.
> > The more I read it, the more it gets complicated.
> 
> In addition to getting some clarification that I can provide to this gentlemen, perhaps this is also an opportunity to make the specification clearer so that such questions do not need to asked. I have never used MarkToBase, so I am at a loss.
> 
> Regards...
> 
> -- Ken
> 
> 
> 
>  
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