The code examples in the online version can be directly copied and pasted into Cuis-Smalltalk. This is why the assignment character “←” you see in the developer Cuis-Smalltalk window is printed as “:=” in the online version of the book. The same applies with the return character “↑” printed as “^” in the online version.

but even ᴡindows® Notepad tries to substitute unknown characters from glyphs in other fonts instead of using the replacement character directly. Sometimes it even substitute characters whereas they exist in the font

How I can know which glyph the font does not support in that list?

Mono doesn't have that glyph, so what you're seeing is that that symbol is being used from another font to be able to show something

To check whether the music symbol ♫ is being displayed in a string (if it is not being displayed on some devices), you can try measuring the string width; if width == 0 then the symbol is absent.

I have a custom font which is displaying the box character.

I want to check if the String I am about to display can be displayed by my custom font.

I can't find a method to check if my Typeface can display a particular String though.

Glyph 0 must be assigned to a .notdef glyph. The .notdef glyph is very important for providing the user feedback that a glyph is not found in the font. This glyph should not be left without an outline as the user will only see what looks like a space if a glyph is missing and not be aware of the active font’s limitation.

It is recommended that the shape of the .notdef glyph be either an empty rectangle, a rectangle with a question mark inside of it, or a rectangle with an “X”

You need .notdef, unicode value undefined: microsoft.com/typography/otspec/recom.htm Characters are assigned in blocks of the same kind. Most blocks have some unassigned points at the end to start the next block on a round number. These points allow Unicode Consortium to add new glyphs to a block. New glyphs don't come into existence often. See typophile.com/node/102205. Maybe you can ask your question in the Typophile forum. They can tell you more about how this exactly works and how to render .notdef

I wasn't aware of 'missing character glyph', some Googling suggests that U+0000 can/should be used for missing characters in the font. However in at least one font I've tested with U+0000 is rendered as whitespace while missing characters are rendered as squares (similar to U+25A1).

I want to be able to detect if the font used can display a certain character or not

At one time the replacement character was often used when there was no glyph available in a font for that character. However, most modern text rendering systems instead use a font's .notdef character, which in most cases is an empty box (or "?" or "X" in a box[5]), sometimes called a "tofu" (this browser displays 􏿾). There is no Unicode code point for this symbol.

No, there is no “glyph not found” character. Different programs use different graphic presentations. An empty narrow rectangle is a common rendering, but not the only one. It could also be a rectangle with a question mark in it or with the code number of the character, in hexadecimal, in it.

The glyph-not-found character is specified by the font engine and by the font; there is no fixed character for it.

By the way, I am not talking about � (replacement character). This one is displayed when a Unicode character could not be correctly decoded from a data stream. It does not necessarily produce the same glyph:

missing glyph

There is no standardized look/glyph, it’s up to the implementation

SVG 1.1 (a W3C Recommendation): The altglyph element provides detailled control over the glyphs used to render particular character data.

A character exists, but the glyph to display it isn't available.

Type designers usually do not create new characters, i.e. the meanings of those pictures, or, more technically put, ‘the smallest component of written language that has semantic value.’ We don’t invent alphabets, we merely re-interpret existing ones.

Type designers create new glyphs, i.e. pictures representing characters.

Characters versus glyphs

A glyph can also represent more than one character at once. Take an f_f_f ligature as an example. It represents three f characters in a row. Ligatures do not have Unicodes, because the separate characters already have codes and the the fact that it’s a ligature does not change the meaning of its parts.

What if you want to share the same glyph shape between two Unicode values? There are a few situation where you would need that. E.g., the symbol increment U+2206 and the Greek letter Delta U+0394 should look the same. There is a similar issue with Ohm U+2126 and Omega U+03A9. Or, you are creating an all-caps font. Or you simply want to reuse the same space glyph for both the space U+0020 and non-breaking space U+00A0.

$ python checkfont.py /usr/share/fonts/**/DejaVuSans.ttf 65 12622 # a ㅎ

The script takes as arguments the font path and optionally code points / characters to search for:

Determine if a glyph exists in a given font

I'm looking to see if there is a way, in PHP, to determine if a glyph exists for a given character in a font.

And get a list of characters in a font like this:

All glyphs are Unicode glyphs!

Characters are logical text units identified by Unicode codepoints, whereas glyphs are graphical font units. The distinction between character and glyph is critical to understanding FontLab, and fonts in general.

A Glyphset is the glyph repertoire of a font, i.e. all glyphs present in the font. The old term for this repertoire was “character set”, but it is misleading because in modern font technology, a font is a collection of glyphs, not a collection of characters.

The use of U+212B 'Angstrom sign', which was encoded due to round-trip mapping compatibility with an East-Asian character encoding, is discouraged, and the preferred representation is U+00C5 'capital letter A with ring above', which has the same glyph.