Re: [ft] Unicode normalization

[mpsuzuki]

Hi,

On Mon, 3 Sep 2007 13:23:40 +0200
<address@hidden> wrote:
>Hi,
>is freetype capable of dealing with the unicode normalization forms?
>I've tried to render these two examples glyph by glyph in order to
>get the desired result:
> 
>Syntax: desired_result = first_glyph_rendered + second_glyph_rendered + ...
> 
>0x00E4    =    0x0061 + 0x0308

>The first one worked just fine.

You wrote the 1st case works well, but I suppose it's
dependent with font. The font you used for testing
may provide non-spacing character @ U+0308, so rendering
text U+0061 + U+0308 makes U+0308 glyph overstriking on
the top of U+0061. But it is possible to implement
a font which assigns spacing character (with dotted-
circle) @ U+0308. Such kind of font is also permitted.

>0x01DE    =    0x0041 + 0x0308 + 0x0304

>But in the second one both combining
>characters (308+304) had been placed at the same
>position instead of on top of each other. So is
>there actually a reliable way to render normalized
>unicode characters composed of more then one combining
>character with freetype?

I suppose you found a simply  overstriken junk of 3
glyphs, because U+0308 & U+0304 are not tuned their
positions.

Today, it is classified as legacy and deprecated way
for TrueType font to display an accented Latin character
by overstriking of base Latin alphabets and diacritical
marks. The recommended way is using an intelligent font
formats like OpenType or TrueType GX. In these font
formats, various precomposed glyph (e.g. 0x00E4, 0x01DE
etc etc) are included, even if they are not coded in
Unicode. In addition, the ruleset to compute precomposed
glyph index from a serie of "component" glyph index is
also included in the font. The OpenType or TrueType GX
renderer compute an index of precomposed glyph (e.g.
glyph index for U+01DE) from given serie of component
glyphs (e.g. 3 glyph index for U+0041, U+0308, U+0304),
and display the precomposed glyph at once. It does not
overstrike 3 component characters on graphic device.

FreeType supports it? No. At least, FreeType2 does not
support OpenType layout system (you have to compute
the glyph index of precomposed glyph out of FreeType2).
I recommend you to check OpenType renderes like Pango
or ICU.

Regards,
mpsuzuki