Manipulate and Substitute TrueType Fonts

Aspose.Words requires TrueType fonts for a variety of tasks, including rendering documents to fixed-page formats, for example, PDF or XPS. When Aspose.Words renders a document, it needs to perform embedding and subset embedding of TrueType fonts into the resulting document, which is a normal practice during a document generation, including popular PDF or XPS formats. This ensures that the document will appear the same to any viewer. Moreover, the XPS specification requires fonts to always be embedded in the document.

To ensure Aspose.Words accurately measures the characters and successfully embeds relevant fonts, the following conditions must be met:

Aspose.Words should be able to find and access TrueType font files on the system.
There must be sufficient TrueType fonts available to Aspose.Words, preferably with the same font family names as the ones used in the document.

Note that the font in the document represents an entity, such as family name, style, size, color, that is different from the TrueType font (physical font) entity. Aspose.Words resolves the font in the document to a physical font at some stage of processing. This enables certain tasks, most commonly the task of calculating text size during layout construction and embedding/subsetting to fixed-page formats. A number of other less popular tasks, such as font resolving and substitution while loading HTML or embedding/subsetting to some flow formats, are likewise enabled.

Font Manipulation and Performance Issues

All available font manipulation mechanisms are contained in the FontSettings class. This class is responsible for fetching fonts within defined font sources as well as for the Font Substitution process, as described below.

Fonts are parsed in several steps:

Obtaining info for font, resolving from all available fonts.
Parsing the resolved fonts to get available glyphs and metrics (horizontal and vertical).
Parsing the resolved fonts for embedding and subsetting.

When Aspose.Words encounters a font in the document for the first time, it attempts to obtain basic font information, such as the font full name, family name, version, style, from the font files located in each font source. After all the fonts are retrieved, Aspose.Words uses these details to find the required font data or a suitable replacement for the requested font.

Since the procedure described above is time-consuming, it may negatively affect application performance at its first launch. However, each instance of FontSettings has its own cache, which could reduce the processing time of subsequent documents. For example, you can share an instance of the FontSettings class between different documents, which allows you to speed up the loading of the documents. The following example demonstrates this:

In the case when FontSettings is not defined explicitly, Aspose.Words uses the default FontSettings instance. This instance is also automatically shared among documents, and can be extracted as follows:

If you are sure that all processing documents require the same font settings, then it is recommended to set up and utilize the default FontSettings instance. Suppose that you need to use the same font sources for all your documents. In this case, you can just amend the default instance as follows:

The custom FontSettings have higher priority than the default instance.

Font Availability and Substitution

A text in a document can be formatted with various fonts, such as Arial, Times New Roman, Verdana, and others. When Aspose.Words renders a document, it attempts to select the fonts that are specified in the document.

However, there are situations when the exact font cannot be found and Aspose.Words must substitute it for a similar font instead. Aspose.Words selects the font according to the following process:

Aspose.Words tries to find a font among the available font sources with an exact font name.
Aspose.Words tries to find the required font among the fonts embedded in the original document. Some document formats such as DOCX can contain embedded fonts.
If Aspose.Words is unable to locate the required font with the exact name match, and the alt_name property defined for this font, then Aspose.Words will find the font defined with alt_name from the FontInfo class, which specifies the font information.
If Aspose.Words is unable to locate the defined font, and alt_name is not also defined, then the font substitution rules are applied one-by-one, as described below (when the appropriate replacement is found, the Font Substitution Process stops and the next step is not executed):
1. First, Aspose.Words tries to process the font name to get the substitution, particularly it tries to remove suffixes with “-” and “,” separators.
  If this substitution rule takes place, a “Font ‘’ has not been found. Using ‘’ font instead. Reason: font name substitution.” warning appears.
2. Then Aspose.Words attempts to apply OS font settings, if they are available, by using the FontConfig utility. This Non-Windows feature must be used with a FontConfig-compatible OS. Almost any Unix-based OS already has a FontConfig library that is designed to provide system-wide font configuration, customization, and access to applications. Otherwise, this library can be easily installed by the user. Aspose.Words knows how to query data and interpret FontConfig results for its own purposes. By default, the FontConfig utility is disabled. You can enable it as follows:
```
fontSettings.substitution_settings.font_config_substitution.enabled = True
```
3. The next step uses a simple but powerful mechanism called Table substitution rule. By default, this feature is active and available for the given operating system. Aspose.Words will substitute the font with this rule if it is not substituted with the FontConfig substitution rule.
  Aspose.Words uses XML tables, which define the basic substitution rules for different OS. According to the Table substitution rule, the list of substitute font names will be used.
  XML
```
<TableSubstitutionSettings xmlns="Aspose.Words"> 
<SubstitutesTable> 
<Item OriginalFont="Arabic Transparent" SubstituteFonts="Arial" /> 
… 
</SubstitutesTable> 
</TableSubstitutionSettings>
```
  The main feature of this rule is the ability to load your own substitution tables, as it is shown in the following example:
```
fontSettings.substitution_settings.table_substitution.load("Table.xml")
```
  Despite flexibility of this mechanism, there are some cases when it is better to disable it, as shown below:
```
fontSettings.substitution_settings.table_substitution.enabled = False
```
4. The FontInfo substitution rule will be applied if the table substitution rule cannot find the font. This mechanism is enabled by default. Aspose.Words finds the most suitable font according to the font information contained in a particular document. This information can be obtained from the FontInfo class as shown below:
```
fontInfos = doc.font_infos
```
  Users cannot interfere in the workflow of this feature, unless they decide to disable it in case of unsatisfactory results:
```
fontSettings.substitution_settings.font_info_substitution.enabled = False
```
  If FontInfo is not available for the missing font, then the process stops.
5. DefaultFont substitution rule will be applied in the case when the FontInfo substitution has also failed. This rule is also enabled by default. According to this rule, Aspose.Words will attempt to use the default font specified in the default_font_name property. If the user has not chosen their own default font, then “Times New Roman” will be used as the default font. This rule can be disabled as shown below:
```
fontSettings.substitution_settings.default_font_substitution.enabled = False
```
  To check the current default font, use:
```
fontSettings.substitution_settings.default_font_substitution.default_font_name
```
  To set up your own replacement option, apply:
```
fontSettings.substitution_settings.default_font_substitution.default_font_name = "Arial"
```
If Aspose.Words is unable to perform the font substitution, it tries to get the first available font from available font sources.
Finally, if Aspose.Words cannot find any fonts among the available font sources, it renders the document using the free Fanwood font that is embedded into the Aspose.Words package.

If FontInfo is available, the FontInfo substitution rule will always resolve the font and override the default font rule. If you want to use the default font rule, you should disable the FontInfo substitution rule. Note that the FontConfig substitution rule will resolve the font in most cases, and thus overrides all other rules.

Font FallBack Settings from XML

There are two different mechanisms used in Aspose.Words — Font substitution and Font fallback. Font substitution is used when the font specified in the document could not be found among the font sources as it was described in the above sections. The Font fallback mechanism is used when the font is resolved, but it does not contain a specific character. In this case, Aspose.Words tries to use one of the fallback fonts for the character.

There is a build_automatic method that automatically builds the fallback settings by scanning available fonts. Since this method may produce a non-optimal fallback setting, you can control the font fallback behavior by using the properties of the FontFallbackSettings class. This class specifies settings of the font fallback mechanism. You can get an instance of the FontFallbackSettings class as follows:

settings = fontSettings.fallback_settings

Similarly to Table substitution rule, this mechanism uses XML tables for configuration. These XML tables can be loaded and saved with the following methods:

fontSettings.fallback_settings.load("MyNewFallbackTable.xml")
fontSettings.fallback_settings.save("Current_FallbackTable.xml")

The Aspose.Words release includes two tables: MsOfficeFallbackSetting.xml and NotoFallbackSetting.xml.

The MsOfficeFallbackSetting table defines a replacement strategy for a range of characters, which is similar to the strategy used by Microsoft Word. Thus, the strategy requires the installation of Microsoft Office fonts. MsOfficeFallbackSetting can be activated using the following method:

fontSettings.fallback_settings.load_ms_office_fallback_settings()

The NotoFallbackSetting table is created especially for use with Google Noto fonts (see more about Google Noto font settings in the next section) and can be enabled as follows:

fontSettings.fallback_settings.load_noto_fallback_settings()

The following code example demonstrates how to load font fallback settings from an XML file:

In the above code example, the following XML file is used:

<FontFallbackSettings xmlns="Aspose.Words">
    <FallbackTable>
        <!-- Fallback table consists of the rules. Each rule defines the fallback fonts which Aspose.Words should use for specified Unicode ranges and base fonts. Rules are checked one by one and the first applicable fallback font is used. If none of the rules are applicable then ".notdef" glyph (missing glyph) from the base font will be used. -->
        <!-- This rule defines that "Vijaya" fallback font should be used for "U+0B80..U+0BFF Tamil" Unicode block. -->
        <Rule Ranges="0B80-0BFF" FallbackFonts="Vijaya"/>
        <!-- This rule defines that "Segoe UI Emoji" and "Segoe UI Symbol" fallback fonts should be used for "U+1F300..U+1F5FF Miscellaneous Symbols and Pictographs", "U+1F600..U+1F64F Emoticons" Unicode blocks. If "Segoe UI Emoji" font does not contains the glyph for the requested Unicode code point then "Segoe UI Symbol" will be checked. -->
        <Rule Ranges="1F300-1F64F" FallbackFonts="Segoe UI Emoji, Segoe UI Symbol"/>
        <!-- This rule defines that "Arial" fallback font should be used for "U+2000..U+206F General Punctuation", "U+2070..U+209F Superscripts and Subscripts" Unicode blocks and specific "U+20B9 INDIAN RUPEE SIGN" code point. -->
        <Rule Ranges="2000-206F, 2070-209F, 20B9" FallbackFonts="Arial" />
        <!-- These rules defines that for "U+3040..U+309F Hiragana" Unicode block "MS Gothic" fallback font should be used if base font is "Times New Roman" and "MS Mincho" fallback font for all other base fonts. -->
        <Rule Ranges="3040-309F" FallbackFonts="MS Gothic" BaseFonts="Times New Roman"/>
        <Rule Ranges="3040-309F" FallbackFonts="MS Mincho"/>
        <!-- This rule defines that "Arial Unicode MS" fallback font should be used if applicable fallback font was not found by previous rules. -->
        <Rule FallbackFonts="Arial Unicode MS"/>
    </FallbackTable>
</FontFallbackSettings>

Predefined Font FallBack Settings for Google Noto Fonts

Aspose.Words provides predefined font fallback settings for Google Noto fonts. These are free fonts licensed under SIL Open Font License, that can be downloaded from Google Noto Fonts. The FontFallbackSettings class provides a load_noto_fallback_settings method. It loads predefined fallback settings, which use Google Noto fonts as shown in the code example below:

Only Sans style Noto fonts with regular weight are used in the predefined settings.

Where Aspose.Words Looks for Fonts

Aspose.Words attempts to find TrueType fonts on the file system automatically. Usually, you can rely on the default behavior of Aspose.Words to find the TrueType fonts, but sometimes you need to specify your own folders containing TrueType fonts. The Specifying TrueType Fonts Location topic describes how and where Aspose.Words looks for fonts, as well as how to specify your own font locations.

Differences in Processing of Font Formats in Aspose.Words and Microsoft Word

There are some differences in processing of font formats in Aspose.Words and Microsoft Word as shown in the table below:

	Microsoft Word	Aspose.Words
TrueType fonts and OpenType fonts with TrueType outlines	Supported.	Supported.
OpenType fonts with PostScript outlines	Supported for most scenarios. Embedding to fixed-page formats such as PDF and XPS are not supported. Text is replaced with bitmap images.	Supported for most scenarios, including embedding to fixed-page formats.
OpenType Font Variations	Only named instances are supported. Continuous variations not supported.	Supported for only default instance. Named instances and continuous variations are not supported.
Type1 fonts	Supported on Windows versions prior to 2013 and on MacOS versions. Support is dropped on Windows versions starting from 2013.	Not supported.