Re: Comparion of LogicalFontInstance::ImplGetGlyphBoundRect() between platforms

[Chris Sherlock <chris.sherlock79@xxxxxxxxx>]

On Sun, Oct 30, 2022 at 2:26 AM Chris Sherlock <chris.sherlock79@xxxxxxxxx> wrote:

Sent from my iPhone

On 23 Oct 2022, at 5:20 am, Caolán McNamara <caolanm@xxxxxxxxxx> wrote:

On Sat, 2022-10-22 at 01:42 +1100, Chris Sherlock wrote:

Test name: VclLogicalFontInstanceTest::testglyphboundrect

equality assertion failed

- Expected: 51x82@(7,-80)

- Actual  : 51x83@(7,-80)

I’ve had another look at the code, with some help from Khaled. The

issue is the way in which we do our final rounding. 

On Freetype, it uses 26.6 fixed point, and thus needs it’s own

special FreeType ceil and floor functions. CoreText appears to using

floating point, but the std::ceil and std::floor functions give

slight different results. 

I presume that for mac its CoreTextStyle::ImplGetGlyphoundRect and the
CTFontGetBoundingRectsForGlyphs so could print the numbers we get there
vs the ones we get in FreeTypeFont::GetGlyphBoundRect to verify that.

I’ve added some debugging statements. the Freetype library does its own floor and ceil calculations. it’s looking like it isn’t a risky a rounding error, it is just that Freetype calculates one value and MacOS framework for glyphs calculates it differently.

Patch is https://gerrit.libreoffice.org/c/core/+/142006 if anyone would like to review :-)

Chris

A polite ping to the mailing list as people are now asking me for the rationale behind the patch, could someone please advise the way forward?

Chris