Monkeybread Software - DynaPDF Manual

DynaPDF Manual - Page 53

Complex Text Layout

Page 53 of 839

The alternate font list can be changed arbitrary often with no additional overhead.

The function to manage alternate font lists are:

• ActivateAltFontList() // Activate or deactivate a font list

• CreateAltFontList()

// Create a font list

• DeleteAltFontList()

// Delete a font list

• SetAltFonts()

// Fill a list with data

Font embedding

With exception of CJK scripts (Chinese, Japanese, Korean) complex text layout depends on font

embedding. Fonts must be embedded because glyphs are usually selected with OpenType

layout features. Such glyphs have mostly no Unicode code point and can therefore not be

selected with simple algorithms.

Chinese, Japanese, and Korean scripts are exceptions, because the PDF format supports special

features like CID Fonts in combination with external cmaps, so that fonts for these scripts must

not necessarily be embedded. This is very important because Asian documents contain usually

much more glyphs in comparison to other languages. Therefore, such documents are much

larger. Non embedded CID fonts can be loaded with SetCIDFont().

Complex text layout and form fields

One thing that must be considered is that the support level of complex text layout in Adobes

Acrobat is limited. The support level is comparable with web browsers. That means basic

shaping and the bidirectional algorithm are available, but Unicode bidi control characters are

not supported and mixed languages produce not always correct results.

Since the appearance of form fields should ideally not change when a user activates a field in

Acrobat, DynaPDF strips out all bidi control characters when setting a field value.

This makes sure that the appearance stream can be created in a comparable way and Acrobat is

able to display a field value correctly.

The very same result can be achieved with regular text functions by setting the flag

gfDisableBidiCtrls with SetGStateFlags().

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