How is transformation of code point to final character implemented in Unicode?

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How is transformation of code point to final character implemented in Unicode?

Characters included in BMP as specified by 4 digits,

and those characters outside of BMP contains 5 or 6 digits.

But my doubt is:

how is the finanal character drawed from value of code point? Are the pictures of each character restored in each computer and when displaying just show the matching picture?

Or the final glyph is a computed result of code point itself?

+1 A:

Each Unicode character has a code. The software displaying the character obtains a glyph for that character code - usually from a font installed onto the hosting computer. It then uses the obtained glyph to display the character.

If it can't find a glyph for that character (many fonts for Latin characters completely omit the glyphs used for East Asian languages characters) it formally can't display it. It will then either indicate error or use a supplement glyph meaning that the actual glyph can't be displayed (it can be a question mark or a square or whatever).

sharptooth 2009-09-02 05:51:43

Please be more specific:Do you mean it uses the pre-restored image to display character or computs the image according to the code?

Shore 2009-09-02 05:54:08

With some interesting added complexities for combining characters such as accent marks, and so on...

Jonathan Leffler 2009-09-02 05:56:20

Yes, the font stores how the character looks like - either in vector or raster form.

sharptooth 2009-09-02 05:56:57

@Shore: a font contains a definition of the shape to be drawn for each character; a Unicode font (typically, they are not complete) contains definitions of how to draw a subset of the Unicode characters. The display software knows how to take that definition and show the result on the screen with the correct scaling (size), colour and so on.

Jonathan Leffler 2009-09-02 05:58:11

Is code point uniquely defined in all systems?

Shore 2009-09-02 06:02:00

Nope, each font can contain a different description or not contain any. Usually if a font contains a glyph that glyph looks reasonably similar to those in other fonts.

sharptooth 2009-09-02 06:09:07

It's important to understand that a code point represents a concept of a character (say latin letter S), not how exactly it should look like. If you see a code point you know what character it is and can for example do automatic language-to-language translation even without having a glyph for that code point.

sharptooth 2009-09-02 06:21:33

"Is code point uniquely defined in all systems?" - Yes. A given code point means the same character everywhere. For example, U+2638 is always WHEEL OF DHARAM. However, a drawing environment may or may not have a glyph for it, and the glyphs might differ somewhat from one font to the next, and from one system to the next.

MtnViewMark 2009-09-02 13:48:06

ansaurus

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How is transformation of code point to final character implemented in Unicode?

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