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Fonts and the Script Manager


This Technical Note describes how the Script Manager uses the font family ID to determine a script code.

[Jun 01 1989]


The traps _FontScript, _IntlScript, and _Font2Script all use a font family ID to determine the script interface system code that they return. This Note describes the process, the way the Script Manager renumbers the Chicago font for non-Roman systems, and the equation for calculating Script IDs from font family IDs.

On a Roman system the Chicago 'FOND' is numbered zero, but this causes no confusion since Chicago is also the system font. Non-Roman systems must renumber Chicago so that it will not interfere with the mapping of 'FOND' ID = 0 to the correct system 'FOND'. Typically Chicago is renumbered to 16383.

In Inside Macintosh, Volume V-293, The Script Manager, the descriptions of _FontScript, _IntlScript, and _Font2Script state that the current font identification number (e.g., 'FOND' ID) is used to calculate the correct script code. The equation for calculating script codes from 'FOND' IDs is as follows:

For a specific example, consider the Kyoto font which is one of the fonts included in KanjiTalk. Its 'FOND' ID is 16385. Plugging that value into the equation above, we get: script = ((16385-16384) DIV 512) +1. Which results in a value of one, the script code for the Kanji script system.

Note that this means that script systems other than Roman can only have 512 separate font families. Furthermore, Roman font families (FOND) must not have an ID greater than 16383, and 'FOND' ID 16383 is reserved for Chicago on non-Roman systems.

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So How Do They Work?

_FontScript, _IntlScript, and _Font2Script begin by setting two Script Manager globals, Forced and Default to false. Then the two special font family ('FOND') numbers zero and one are mapped to the System and Application font.

Next the 'FOND' ID is tested to see if it is an international font. _FontScript and _IntlScript simply take the value out of the txFont field of the current grafPort. _Font2Script uses the value passed to it. The test is simply:

IF FONDid < $4000  {16384}
    script is Roman so return 0

Once the script code has been determined, the routine looks at the Script Manager globals FontForce and IntlForce.

If the currently installed script is Roman and fontForce is true, or if intlForce is true and the routine called was _IntlScript, then the value returned will be the current system script. If the installed script is not Roman; the script code calculated will be returned when the routine called was _IntlScript, intlForce is true, and the script code does not equal the system script.

Once the script code to be returned as been calculated, a final check is made to be sure that the script is installed and enabled. If it is not; Roman is returned, and Forced is set to false and Default is set to true.

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What's This Forced Stuff?

Two Script Manager globals, fontForce and intlForce, are flags that support compatibility. Turning fontForce on will cause Roman fonts to be interpreted as belonging to the system script. This provides compatibility for applications that hard-code font numbers.

For example, the Arabic script interface system provides a cdev which lets a user turn fontForce on. When a user does this, any Roman fonts will be mapped to an Arabic font. Note this is only a partially effective measure since the user still does not have complete control over fonts.

It should also be noted that if a user sets fontForce on via the cdev, values returned for fonts with family IDs in the range $0002 to $3FFF (Roman 'FOND' ID range) may vary. This is not a good feature for applications that allow mixed text. To avoid this problem, an application can turn the fontForce flag off before calling _Font2Script or _FontScript. The flag value should be saved before turning it off, and restored later.

The intlForce flag determines how the call IUGetIntl behaves. If this flag is on, IUGetIntl will always return the international resources ('itlx' where x is 0-2) corresponding to the system script. When intlForce is off, the font in the current port will be used to determine which international resources will be returned. This flag lets an application control what date formats, sorting routines, etc. will be used.

For that reason, before calling any of the international utility routines or using the binary to decimal routines, an application should verify that thePort and thePort^.txFont are set correctly, or that intlForce is set properly.

Let's Look at a Picture

The flowchart in Figure 1 illustrates the operation of _FontScript, _IntlScript, and _Font2Script, and how they are affected by the global flags fontForce and intlForce.

Operation Flowchart

Figure 1 - Operation Flowchart

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Inside Macintosh, Volume I-493, The International Utilities Package

Inside Macintosh, Volume V-293, The Script Manager

Inside Macintosh, Volume V-287, The International Utilities Package

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Acrobat gif

Acrobat version of this Note (144K).


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