Apple LaserWriter Pro 630 Envelope Feeder Specifications download pdf (Page 87)

CHAPTER 4

TrueType Fonts

TrueType Font Format

TrueType Code 4

The TrueType font-scaling code is partitioned into three pieces and sent to the device on

demand for each document that uses an

'sfnt'

(scalable font) resource. The code is

encrypted using the Adobe encryption mechanism and depends on the existence of the

eexec

and

cexec

operators.

Because of the way the code is encrypted, the downloadable TrueType code can be used

only on Class B devices and is discarded on all other classes of devices.

You should note the following three requirements:

■

eexec

and

cexec

are deﬁned on a printer, their implementation must be

compatible with Adobe PostScript.

■

Since the TrueType code is encrypted 68000-family code, it will not run on a printer

that is not based on the 68000 family of processors.

■

In the case of the LaserWriter 7.0 driver, the amount of available virtual memory (VM)

on the printer when the driver ﬁrst encounters an

'sfnt'

resource in a document is a

factor in deciding whether the TrueType code is downloaded. If the printer has less

than 120,000 bytes of VM available, the TrueType code will not be downloaded.

Because it is relatively large, TrueType code is partitioned into three physical pieces in

the LaserWriter 7.0 driver. When this code is downloaded, four new operators are

deﬁned in PostScript. A PostScript dictionary,

TrueDict

, is created in which those four

operators (as well as some version information) are stored. One operator is used to

initialize TrueType for each new

'sfnt'

resource, and the others are used within the

BuildChar

procedure in the font.

The TrueType code renders characters in either bitmap or PostScript path form. The path

form is invoked only when a character path is required during rendering via

charpath

or an outline (

PaintType

) style. If the bitmap size for a character exceeds 10,000 bytes

(which is roughly the memory needed for a 100-point character at 300 dpi), the scaler is

asked to band the bitmap, and the character is printed in bands. Future drivers or other

applications may download different operators. If so, these operators will have different

names if their semantics differ from those deﬁned by the LaserWriter 7.0 driver. The

entries in the font dictionary for a Class B printer (deﬁned in “TrueType Font Dictionary

Entries” later in this chapter) remain the same.

Patch 4

The patch, redeﬁnes the PostScript

charpath

operator. It signals whether characters are

to be rendered using the PostScript path or via a bitmap. The patched

charpath

simply

sets a global ﬂag to signal that

charpath

is in effect. This ﬂag is then examined when

characters are being rendered. If the ﬂag is

true

, the characters are always constructed

using a PostScript path rather than a bitmap.

Note

As with the TrueType code, the redeﬁnition of PostScript operators is

ignored on Class A and Class C devices.

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Apple LaserWriter Pro 630 Envelope Feeder Specifications Page 87

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