Comparion of LogicalFontInstance::ImplGetGlyphBoundRect() between platforms

Chris Sherlock chris.sherlock79 at
Sat Oct 29 15:26:22 UTC 2022

Sent from my iPhone

> On 23 Oct 2022, at 5:20 am, Caolán McNamara <caolanm at> 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 if anyone would like to review :-)

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