White On Black VF versus Black On White VF is a pair of special-purpose Variable Fonts that are intended to exemplify a serious rendering issue when a white glyph is on a black background, while a black glyph on a white background has no issues. The inner contours that represent CJK Unified Ideograph U+91D1 金 (meaning gold or metal) are identical other than winding direction. The weight axis further demonstrates that overlap removal is not a viable solution because the topology changes.
The only functional glyph in both Variable Fonts is for U+328E ㊎ (an annotated form of 金, which serves as an abbreviated form of 金曜日 that means Friday, a day of the week), but in reversed (white on black) form in the White on Black Variable Font in order to demonstrate this rendering issue. A real-life example of the reversed (white on black) form is Adobe-Japan1-7 CID+10758. The Adobe-Japan1-7 Character Collection includes over 800 such glyphs, and there are hundreds of OpenType/CFF Japanese fonts that include such glyphs.
To build the Variable Fonts from source, you need to have installed the Adobe Font Development Kit for OpenType (AFDKO) tools, along with fontmake to produce the TTF. The AFDKO tools are widely used for font development today, and are part of most font editor apps.
In this repository, all necessary files are in place for building the Variable Fonts, and the build.sh file can simply be executed.
For any suggestions for changes, please create a new issue for consideration.