Is there any unicode character whose character is missing in all fonts?

Question

On Android, I want to determine if the font used can display a specific character or not, but as I understand it, this is not possible using the usual means, as indicated Check if a custom font can display a character

To find this out, I write the character I want to check into a bitmap, and then I write another character that, as I know, is missing from another bitmap and compares the contents of the bitmap images. If they are equal, the symbol is absent.

The question is, is there any Unicode character for which the glyph (more or less) is guaranteed to be absent from the fonts commonly used on Android phones?

The Unicode replacement character sounds promising when you read about it on Wikipedia:

It is used to indicate problems when the system cannot map the data stream to the correct character. This is most often observed when the font does not contain a character, but also appears when data is invalid and does not match the character

However, after a little testing, I see that this character is not used to represent the missing glyphs on my computer running Windows 7 or on the Android phone with which I tested (Motorola Atrix).

Answer 1

There is no Unicode value assigned to a glyph that is used to display glyphs that are not in the font used. In the actual font, the glyph identifier 0 should always be . Notdef glyph , which is used for all characters that do not have a glyph. However, this information cannot be used for fonts on Android, so it is not possible to use the .notdef glyph.

There are many reserved / unassigned code points in Unicode, and my limited testing shows that these code points are rendered using the .notdef glyph. Thus, using U + 0978 , which is the reserved code point in the middle of the Devanagari block , I can determine if there is any other valid known character in the font that I want to check.

This is not future proof, as new characters may be added to reserved code points by the Unicode Consortium in the future. But for my needs, this is good enough, since I want to do, this is a temporary thing that no longer has to do with the near future.

Update:

The decision to see U + 0978 did not work out for a long time. This character was added in Unicode 7.0 in June 2014. Another option is to use a glyph that exists in Unicode, but is unlikely to be used in a regular font.

U + 124AB in the early dynastic cuneiform is probably something that does not exist in many fonts at all.