[HarfBuzz] Eager CS undergrad thirsty for knowledge about the inner bowels of typeface rendering. Specifically for supporting vertical ligature caret definitions.

[Ariel Malka]

Hi Robin,

That's a huge puzzle you're trying to assemble, and I'm not sure adding two
big topics like C++ and OpenGL is the best idea...

Anyway, I have recently created a github repo which allows to start
experimenting with Harfbuzz in a "relatively easy" way:
https://github.com/arielm/Unicode

HTH and good luck with your exploration,

Ariel
http://chronotext.org


On Tue, Jan 28, 2014 at 2:32 AM, Robin Skahjem-Eriksen <
robinds at student.matnat.uio.no> wrote:

> I have started to investigate into the matter and I find that there is
> very sparse information readily available. Microsoft had a very interesting
> document, which I have been trying to understand:
> http://www.microsoft.com/typography/OpenTypeDev/tibetan/intro.htm
> In the section "Examples of Tibetan" (bottom of document), the first
> example shows how a sequence of eight code points are strung together to
> form a Tibetan "syllable". It's not really a syllable. It's called a
> tsheg-bar in Tibetan and a Tibetan word can consist of multiple of these.
> Anyways, all the code points from the second one up to and including the
> fourth one are as far as I can tell formed into a ligature. I have opened
> the MS Himalaya font in Fontforge and seen that this ligature is defined as
> "tibSa_Ga_Rata_Shapkyu" in a location outside of the Unicode address space.
>
> Now, if a user is to work with Tibetan text like any other user of a roman
> script language, the user of Tibetan script would be very disappointed. The
> reason for this is that it is impossible to place the caret and select
> individual characters in this ligature. As of now, you can only select the
> entire stack as a whole selection. This is partly because the glyphs have
> been transmuted into a ligature, but perhaps also because there seems to be
> no definitions of vertical caret ligatures anywhere.
>
> How would one go about defining such an important feature? Should this be
> implemented in the font? Should it be implemented in the software that
> handles the type face? Or perhaps both? While digging through the MS
> Himalaya font, I found that there is a value for a Ligature Caret Count.
> What is this value supposed to be used for? For the ligatures that are
> supposed to represent stacks of multiple glyphs, the Ligature Caret Count
> had values up to 4, which I hope can mean that the font itself contains the
> information I am looking for. Is my assumption correct?
>
> Also. I am highly willing to learn more about the inner bowels of typeface
> rendering. I have taken a course on Computer design and understand how
> everything are bits and how Asssembly language and C handles this. I also
> understand the general idea about Unicode and how this is defined on a low
> level. I've also understood that fonts are basically Bézier curves which
> are rasterized to the screen buffer. There is still a lot of this process
> which I still find very murky, so if anybody knows any in depth reading
> material, I would be very happy to start reading those. I have read State
> of Text Rendering by Behdad Esfahbod, which was a great overview of the
> text rendering stack. But I would really like to get more in depth
> understanding of each layer in the stack.
>
> I would really like to also learn more about Harfbuzz and how to work on
> it. I would really love to spend some time working on it, if I am at a
> level where my code submission would be acceptable to the standards of this
> project. Is there any documentation for Harfbuzz? I've taken a quick glance
> at the source code and run some scripts and make commands, but I honestly
> don't know what's going on. Why are the C files named .cc and some of the
> header files named .hh? I can recognize some font lingo and have a slight
> understanding of what might be going on, but it would be really helpful to
> have something like this for an Openfont file: http://imgur.com/a/JEObT#0.
> I must also say that I have no idea of what harfbuzz is supposed to do and
> how I test or use it once it's compiled. I've tried running some shell
> scripts and bin files that were compiled, but I really have no clue.
>
> Is there somewhere I can learn how to get a handle on understanding the
> technicalities of the Harfbuzz project and learn what I need to start
> contributing?
>
> Sincerely,
> Robin Skahjem-Eriksen
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