Core Text doesn't actually have a concept of DPI internally, as it
doesn't rasterize anything by itself, it just generates vector paths
that get passed along to Core Graphics.
In practice this means Core Text operates in the classical macOS
logical DPI of 72, with one typographic point corresponding to one
point in the Core Graphics coordinate system, which for a normal
bitmap context then corresponds to one pixel -- or two pixels for
a "retina" context with a 2x scale transform.
Scaling the font point sizes given to HarfBuzz to an assumed DPI
of 96 is problematic with this in mind, as fonts with optical
features such as 'trak' tables for tracking, or color glyphs,
will then base the metrics off of the wrong point size compared
to what the client asked for.
This in turn causes mismatches between the metrics of the shaped
text and the actual rasterization, which doesn't include the 72
to 96 DPI scaling.
If a 96 DPI is needed, such as on the Web, the scaling should be
done outside of HarfBuzz, allowing the client to keep the DPI of
the shaping in sync with the rasterization.
The recommended way to do that is by scaling the font point size,
not by applying a transform to the target Core Graphics context,
to let Core Text choose the right optical features of the target
point size, as described in WWDC 2015 session 804:
https://developer.apple.com/videos/play/wwdc2015/804/
Catch missing imports and errors like #1520 and #1521
__E901,E999,F821,F822,F823__ are the "_showstopper_" [flake8](http://flake8.pycqa.org) issues that can halt the runtime with a SyntaxError, NameError, etc. Most other flake8 issues are merely "style violations" -- useful for readability but they do not effect runtime safety.
* F821: undefined name `name`
* F822: undefined name `name` in `__all__`
* F823: local variable name referenced before assignment
* E901: SyntaxError or IndentationError
* E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree
* src/hb-cff-interp-dict-common.hh: Use ull for unsigned int64_t
The llu suffix does not work for older Visual Studio versions
(pre-2013), but ull works for all the compilers that we attempt to
support.
* test/api: Fix build on pre-C99 compilers
Ensure variables are declared at the top of the block.
* src/hb-dsalgs.hh: Add specialization for hb_is_signed<> for __int8
Pre-Visual Studio 2010 does not consider __int8 (which is typedef'ed to
int8_t) to be equivilant to signed char, so the compiler cannot find the
corresponding hb_is_signed<> specialization that is needed.
The interesting thing is unsigned __int8 is considered to be equivilant
to unsigned char, so as the other types (short, int, long) that we look
for here, so only the specialization for __int8 is added here.
This will fix builds on Visual Studio 2008 at least.
* add fd index checks to subr subsetter
also added oss-fuzz test case
* undid SubrSubsetParam::is_valid
because already validated by SubrClosures.valid
It is not visually noticeable but apparently affected by kern format2 correct implementation.
I should've checked CoreText result which can't as CircleCI outage.
Tor Arne Vestbø
Behdad Esfahbod
cclauss
fanc999
Michiharu Ariza
Ebrahim Byagowi
David Corbett
Chun-wei Fan