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/
Rewrote struct FDSelect3_4.ranges as ArrayOf
Updated FDSelect3_4::sanitize () to call ranges.sanitize ()
nRanges now a function to return a reference to ranges.len
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
In Python 3, __reload()__ was moved and __sys.setdefaultencoding()__ because the default is already utf-8. Also __Error()__ is an _undefined name_ and __Exception()__ creates a generic exception.
Behdad Esfahbod
Tor Arne Vestbø
Michiharu Ariza
Ebrahim Byagowi
Nathan Willis
cclauss