[cairo] Custom UserFont sizing questions

[Behdad Esfahbod]

Ian Britten wrote:
> Hi all,
> I'm down inside the 'render' function for my custom UserFont, and
> am struggling with some size/scale issues.  I'm hoping someone can
> help explain what I'm seeing, and how to best address+simplify it.
> 
> First though, if my render function simply draws my FT_Face using
> glyph_path(), then everything is sized ok.  :) As such, I'm
> pretty sure I've got everything set up correctly in my higher-level
> code regarding the font matrix, context transformation, etc.
> 
> However, I now need to render my face using raw FT calls.

Why exactly?

behdad


>  I've
> got the code laid out and running, but with some some issues
> getting it sized/scaled correctly.  (NB: All the other calling
> code is the same - It's just a different 'render' implementation)
> 
> Basically, my (cairomm) render code looks like:
>        FT_Set_Char_Size(face, 0, mmToPoint(115.238887) * 64,
>                         72, 72);
>        FT_Load_Glyph(face, glyph, load_flags);
>        inContext->save();
>        inContext->scale(0.001158/2.0, -0.001158/2.0);
>        FT_Outline_Decompose(face->glyph->outline, &funcs, &data);
>        inContext->restore()
>        inContext->stroke();
> 
> Now, as to the hard-coded numbers:
>    - 115.23887 is the mm size my glyph should be rendered on the
>      PDF output, from the higher-level calling code.
>    - 0.001158 is the user size of my glyph (as set into the font
>      matrix of the context).  Again, from the calling code.
>    - The 2.0 is unknown, and may not be exactly correct.  I've
>      just been flailing with it to get generally-correct results.
> 
> Now,
> - Can someone explain the 2.0?  I don't understand it...
> - I'm reasonably sure I can get those other numbers properly
>    passed into my render function if necessary, but can someone
>    suggest an approach that maybe doesn't require them?  The
>    'render' docs talk about 'font space' and a size of 1.0, giving
>    the impression that I maybe shouldn't need them, but I just
>    can't seem to get it to work otherwise.  :(
>    Also, since I didn't need these numbers when just using
>    glyph_path(), I'm inclined to think I shouldn't need them
>    now either.  I tried to trace though the glyph_path() code,
>    but couldn't really find/understand what I needed...
> 
> I know I'm in a pretty specialized piece of Cairo, and I'm
> doing something even more specialized, but I'm hoping someone
> out there might be familiar with the relevant pieces and can
> help explain+simplify!
> If anything is unclear, or if you need/want more detail, just
> ask...
> 
> Many thanks for any help or suggestions!
> Ian
> 
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