>>> Thanks, I will review this shortly.  Meanwhile, could you please look
>>> at how Emacs with this patch displays some complex Emoji sequences?
>>> Some of them look incorrect to me.  For example, this sequence from
>>> admin/unidata/emoji-zwj-sequences.txt:
>>>
>>>     1F469 200D 1F469 200D 1F467 200D 1F466      ; RGI_Emoji_ZWJ_Sequence  ; family: woman, woman, girl, boy                                # E2.0   [1] (👩‍👩‍👧‍👦)
>>>
>>> when displayed using Segoe UI Emoji, is shown with the "boy" part
>>> overlapping the closing parenthesis, which looks incorrect to me.
>>> "C-u C-x =" claims all of the codepoints of the sequence were composed
>>> into a single grapheme cluster, but it doesn't look like that on
>>> display, and the cursor doesn't include the "boy" part.
>>
>> I dont's see that, but I do see that the individual glyphs are truncated
>> on the left side, even when removing color rendering.  Do you see
>> it?
> 
> Yes.
> 
>> I will investigate this first, in case the defects are related.

This patch fixes the left side glyph truncation, which happens when 
glyphs have negative left bearing.

About the problem you reported, I can't reproduce when building for 
64bit. It does show when building with mingw32 for 32bit. It also shows 
when building version 30.0.92. Maybe is the Harfbuzz version? I have 
2.4.0 for this build.