[cairo] NO_HINTING problems with custom FT_Face
Ian Britten
britten at caris.com
Thu Oct 15 06:44:57 PDT 2009
Ian Britten wrote:
> I was hoping that someone could help me get to the root of a problem
> I'm having when using my custom FreeType font driver via Cairo.
[ snip ]
> Problem:
> - When I create+draw my text upright and use load_flags=0, the text
> draws as expected. However, when I use load_flags=FT_LOAD_NO_HINTING,
> my text no longer draws.
[ snip ]
Ok, here's some more info that I hope will illuminate something for
someone:
Attached are two stack traces, showing the calls between my call to
cairo_show_glyphs() until my slotLoadCB() is called, to load the
requested glyph. The two traces are for the two cases where
load_flags=0 (DEFAULT.txt), and where load_flags=FT_LOAD_NO_HINTING
(NOHINTING.txt). DEFAULT.txt is the case that works.
The flow through the Cairo code seems to be the same until Cairo
calls FT_Load_Glyph(). In the working case (DEFAULT.txt), the
code goes through some extra FT calls (Autohinter?) while in the
non-working case, the FT_Load_Glyph() calls my slotLoadCB().
I should note that my slotLoadCB() is actually called twice from
cairo_show_glyphs() - Once as shown in the attachments, and a
second time via _cairo_surface_old_show_glyphs_draw_func()/etc.
Since the parameters to my slotLoadCB() were the same in both
cases, I didn't bother to include the second traces here. However
I can, if requested.
So, is anyone familiar with this FT autohinter stuff, and does
it's presence/absence alter what Cairo does with glyphs? Might
I be in an untested (broken?) code path (ie: Rendering text with
hinting turned off)? Is there any other info I could offer to
help get to the bottom of this?
Many thanks for any help...
Ian
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