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Tor Arne Vestbø 6f9e444c28 harbuzzng: Remove assumption about Core Text working in 96 DPI
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/

GitHub-PR: https://github.com/harfbuzz/harfbuzz/pull/1484
Change-Id: I830f0cd7a82552422bbe09226e2d571e246fe3f4
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
2019-02-11 01:41:32 +00:00
bin syncqt: Do not clean header directory before "-minimal" run 2018-11-22 14:16:53 +00:00
config.tests x86: Disable AVX support on 64-bit MinGW 2019-02-06 08:11:29 +00:00
dist Add changes file for Qt 5.12.1 2019-01-21 16:47:48 +00:00
doc Merge remote-tracking branch 'origin/5.12.1' into 5.12 2019-01-23 10:13:29 +01:00
examples Use requestUpdate instead of timer in a few GL examples 2019-01-22 21:25:39 +00:00
lib
mkspecs Android: follow official android flags for cmake 2019-02-07 09:02:17 +00:00
qmake Make the Makefile a dependency of default targets for nmake 2019-02-04 08:10:25 +00:00
src harbuzzng: Remove assumption about Core Text working in 96 DPI 2019-02-11 01:41:32 +00:00
tests Fix two smaller bugs in the BiDi engine 2019-02-09 08:01:26 +00:00
util Clean up and update Unicode character data 3rd-party infrastructure 2018-11-11 22:09:27 +00:00
.gitattributes
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config_help.txt configure: improve warning when all qpa plugins disabled with features.gui 2019-01-07 07:27:35 +00:00
configure configure: Treat win32-clang-g++ the same as win32-g++ 2018-10-10 04:10:40 +00:00
configure.bat configure: Prefer cl.exe over clang-cl.exe 2018-01-04 21:22:42 +00:00
configure.json configure: enable inline tests to contain auxiliary files 2018-12-19 19:22:06 +00:00
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header.BSD Use placeholder for year in header.* files 2018-04-16 11:02:22 +00:00
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header.MIT qsimd: add support for new x86 CPU features 2018-05-05 06:20:07 +00:00
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qtbase.pro nuke configure -host-option 2016-12-13 18:55:59 +00:00
sync.profile Fix build failed with ANGLE 2018-10-16 05:19:43 +00:00