Variable font version could not display some symbols

[WordlessEcho]

Prerequisites

• If you are reporting an issue that affects glyphs for characters for a particular region or regions, did you verify that the characters are within the supported scope of the region or regions? This generally means GB 18030 or Tōngyòng Guīfàn Hànzìbiǎo (通用规范汉字表) for China, Big Five or CNS 11643 Planes 1 & 2 for Taiwan, HKSCS-2016 for Hong Kong, JIS X 0208, JIS X 0212, and JIS X 0213 for Japan, and KS X 1001 and KS X 1002 for Korea.
• Did you thoroughly search the open and closed issues to avoid reporting a duplicate issue?
• Did you go through the official font readme file to better understand the scope of the project, to include the Known Issues section at the very end?

Description

[Please provide here a thorough description of the issue, being sure to specify at least a Unicode code point if it affects a character or a particular glyph for a character. Including the character itself after the Unicode code point also helps, for visual reasons. Images with annotations that pinpoint the issue also help. If you are referencing standards, please keep in mind that they may have known or unknown errors. It is not necessary to provide CIDs.]

Thanks to @AokiFuru simonsmh/notocjk#25.

⚽ (U+26BD), ● (U+25CF), ■ (U+25A0), ◆ (U+25C6), ▲ (U+25B2), ▶ (U+25B6), ▼ (U+25BC), ◀ (U+25C0), ♠ (U+2660), ♥ (U+2665), ♣ (U+2663), ♦(U+2666), ❖ (U+2756), ✚ (U+271A), ✿ (U+273F), ◢ (U+25E2), ◣ (U+25E3), ◤ (U+25E4), ◥ (U+25E5)

Those were displayed correctly in super OTC version.

[RuixiZhang42]

Comment deleted because I was completely off. Sorry for the confusion.

[WordlessEcho]

I use Google's font tool to dump its cmap. (googlefonts/fonttools: A library to manipulate font files from Python.)

<cmap>
    <tableVersion version="0"/>
    <cmap_format_4 platformID="0" platEncID="3" language="0">
    <!-- some maps -->
    <map code="0x25c6" name="uni25C6"/><!-- BLACK DIAMOND -->

Now I am confused.

[punchcutter]

Those characters are in the font and look fine in some apps, but I see them disappear in other apps. What system and software are you using where they don't show up?

[punchcutter]

Actually, something very weird happened and a bunch of those glyph outlines disappeared. My local build is totally fine so we will be doing a new release soon that will fix this.

[WordlessEcho]

Those characters are in the font and look fine in some apps, but I see them disappear in other apps. What system and software are you using where they don't show up?

Windows 10 version 19042.867
In System settings -> personalization -> fonts -> Source Han Sans HC VF -> input a ⚽ (U+26BD) for example

In Source Han Sans HC:

In Microsoft Edge (Chromium version), change font to Noto Sans CJK SC VF in settings -> appearence -> custom fonts
Some symbols fallback to use Emoji font correctly but some not.

Change font-family by developer tools to Source Han Sans SC VF:

Change font-family by developer tools to Source Han Sans SC:

Andorid 11
I change system font config (fonts.xml) to use variable font.

<!-- some family -->
<family lang="zh-Hans">
        <font weight="100" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="100.0" />
        </font>
        <font weight="300" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="300.0" />
        </font>
        <font weight="350" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="350.0" />
        </font>
        <font weight="400" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="400.0" />
        </font>
        <font weight="500" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="500.0" />
        </font>
        <font weight="700" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="700.0" />
        </font>
        <font weight="900" style="normal" index="3">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="900.0" />
        </font>

        <!-- serif font -->
    </family>
    <family lang="zh-Hant,zh-Bopo">
        <font weight="100" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="100.0" />
        </font>
        <font weight="300" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="300.0" />
        </font>
        <font weight="350" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="350.0" />
        </font>
        <font weight="400" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="400.0" />
        </font>
        <font weight="500" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="500.0" />
        </font>
        <font weight="700" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="700.0" />
        </font>
        <font weight="900" style="normal" index="4">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="900.0" />
        </font>

        <!-- serif font -->
    </family>
    <family lang="ja">
        <font weight="100" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="100.0" />
        </font>
        <font weight="300" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="300.0" />
        </font>
        <font weight="350" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="350.0" />
        </font>
        <font weight="400" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="400.0" />
        </font>
        <font weight="500" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="500.0" />
        </font>
        <font weight="700" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="700.0" />
        </font>
        <font weight="900" style="normal" index="1">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="900.0" />
        </font>

        <!-- serif font -->
    </family>
    <family lang="ko">
        <font weight="100" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="100.0" />
        </font>
        <font weight="300" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="300.0" />
        </font>
        <font weight="350" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="350.0" />
        </font>
        <font weight="400" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="400.0" />
        </font>
        <font weight="500" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="500.0" />
        </font>
        <font weight="700" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="700.0" />
        </font>
        <font weight="900" style="normal" index="2">NotoSansCJK-VF.ttc
            <axis tag="wght" stylevalue="900.0" />
        </font>

        <!-- serif font -->
    </family>
<!-- some family -->

In Google Pinyin Method
Before modified (Android 11 use NotoSansCJK-Regular.ttc version 2.001 in default):

After modified:

[tamcy]

@punchcutter In my case it is the autohinter that caused the disappearance of the glyphs. From my observation, the glyph would disappear when the outlines of the two masters are the same (but I do see a few exceptions).

[punchcutter]

@tamcy Thanks for confirming that. I recently found the bug in tx when used to instantiate a CFF2 variable font, but we aren't using that here. I just confirmed I see the same bug with psautohint since it also uses tx so looks like a bug in CFF2 handling.

[punchcutter]

Fixed in 2.004