| title | description | ms.date | dev_langs | helpviewer_keywords | ms.assetid | |||||||
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Optimizing Performance: Text |
Learn how to optimize the performance of text content through use of feature-rich user interface (UI) controls. |
03/30/2017 |
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66b1b9a7-8618-48db-b616-c57ea4327b98 |
WPF includes support for the presentation of text content through the use of feature-rich user interface (UI) controls. In general you can divide text rendering in three layers:
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Using the xref:System.Windows.Documents.Glyphs and xref:System.Windows.Media.GlyphRun objects directly.
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Using the xref:System.Windows.Media.FormattedText object.
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Using high-level controls, such as the xref:System.Windows.Controls.TextBlock and xref:System.Windows.Documents.FlowDocument objects.
This topic provides text rendering performance recommendations.
Windows Presentation Foundation (WPF) provides advanced text support including glyph-level markup with direct access to xref:System.Windows.Documents.Glyphs for customers who want to intercept and persist text after formatting. These features provide critical support for the different text rendering requirements in each of the following scenarios.
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Screen display of fixed-format documents.
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Print scenarios.
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Extensible Application Markup Language (XAML) as a device printer language.
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Microsoft XPS Document Writer.
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Previous printer drivers, output from Win32 applications to the fixed format.
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Print spool format.
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Fixed-format document representation, including clients for previous versions of Windows and other computing devices.
Note
xref:System.Windows.Documents.Glyphs and xref:System.Windows.Media.GlyphRun are designed for fixed-format document presentation and print scenarios. WPF provides several elements for general layout and user interface (UI) scenarios such as xref:System.Windows.Controls.Label and xref:System.Windows.Controls.TextBlock. For more information on layout and UI scenarios, see the Typography in WPF.
The following examples show how to define properties for a xref:System.Windows.Documents.Glyphs object in XAML. The examples assume that the Arial, Courier New, and Times New Roman fonts are installed in the C:\WINDOWS\Fonts folder on the local computer.
[!code-xamlGlyphsOvwSample1#1]
If you have custom control and you want to render glyphs, use the xref:System.Windows.Media.DrawingContext.DrawGlyphRun%2A method.
WPF also provides lower-level services for custom text formatting through the use of the xref:System.Windows.Media.FormattedText object. The most efficient way of rendering text in Windows Presentation Foundation (WPF) is by generating text content at the glyph level using xref:System.Windows.Documents.Glyphs and xref:System.Windows.Media.GlyphRun. However, the cost of this efficiency is the loss of easy to use rich text formatting, which are built-in features of Windows Presentation Foundation (WPF) controls, such as xref:System.Windows.Controls.TextBlock and xref:System.Windows.Documents.FlowDocument.
The xref:System.Windows.Media.FormattedText object allows you to draw multi-line text, in which each character in the text can be individually formatted. For more information, see Drawing Formatted Text.
To create formatted text, call the xref:System.Windows.Media.FormattedText.%23ctor%2A constructor to create a xref:System.Windows.Media.FormattedText object. Once you have created the initial formatted text string, you can apply a range of formatting styles. If your application wants to implement its own layout, then the xref:System.Windows.Media.FormattedText object is better choice than using a control, such as xref:System.Windows.Controls.TextBlock. For more information on the xref:System.Windows.Media.FormattedText object, see Drawing Formatted Text .
The xref:System.Windows.Media.FormattedText object provides low-level text formatting capability. You can apply multiple formatting styles to one or more characters. For example, you could call both the xref:System.Windows.Media.FormattedText.SetFontSize%2A and xref:System.Windows.Media.FormattedText.SetForegroundBrush%2A methods to change the formatting of the first five characters in the text.
The following code example creates a xref:System.Windows.Media.FormattedText object and renders it.
[!code-csharpformattedtextsnippets#FormattedTextSnippets1] [!code-vbformattedtextsnippets#FormattedTextSnippets1]
WPF includes multiple controls for drawing text to the screen. Each control is targeted to a different scenario and has its own list of features and limitations.
In general, the xref:System.Windows.Controls.TextBlock element should be used when limited text support is required, such as a brief sentence in a user interface (UI). xref:System.Windows.Controls.Label can be used when minimal text support is required. The xref:System.Windows.Documents.FlowDocument element is a container for re-flowable documents that support rich presentation of content, and therefore, has a greater performance impact than using the xref:System.Windows.Controls.TextBlock or xref:System.Windows.Controls.Label controls.
For more information on xref:System.Windows.Documents.FlowDocument, see Flow Document Overview.
The xref:System.Windows.Controls.TextBlock element is derived from xref:System.Windows.UIElement. The xref:System.Windows.Documents.Run element is derived from xref:System.Windows.Documents.TextElement, which is less costly to use than a xref:System.Windows.UIElement-derived object. When possible, use xref:System.Windows.Documents.Run rather than xref:System.Windows.Controls.TextBlock for displaying text content in a xref:System.Windows.Documents.FlowDocument.
The following markup sample illustrates two ways of setting text content within a xref:System.Windows.Documents.FlowDocument:
[!code-xamlPerformance#PerformanceSnippet13]
In general, using a xref:System.Windows.Documents.Run within a xref:System.Windows.Controls.TextBlock is more performance intensive than not using an explicit xref:System.Windows.Documents.Run object at all. If you are using a xref:System.Windows.Documents.Run in order to set text properties, set those properties directly on the xref:System.Windows.Controls.TextBlock instead.
The following markup sample illustrates these two ways of setting a text property, in this case, the xref:System.Windows.Controls.TextBlock.FontWeight%2A property:
[!code-xamlPerformance#PerformanceSnippet12]
The following table shows the cost of displaying 1000 xref:System.Windows.Controls.TextBlock objects with and without an explicit xref:System.Windows.Documents.Run.
| TextBlock type | Creation time (ms) | Render time (ms) |
|---|---|---|
| Run setting text properties | 146 | 540 |
| TextBlock setting text properties | 43 | 453 |
Imagine a scenario where you have a xref:System.Windows.Controls.Label object that is updated frequently from a xref:System.String source. When data binding the xref:System.Windows.Controls.Label element's xref:System.Windows.Controls.ContentControl.Content%2A property to the xref:System.String source object, you may experience poor performance. Each time the source xref:System.String is updated, the old xref:System.String object is discarded and a new xref:System.String is recreated—because a xref:System.String object is immutable, it cannot be modified. This, in turn, causes the xref:System.Windows.Controls.ContentPresenter of the xref:System.Windows.Controls.Label object to discard its old content and regenerate the new content to display the new xref:System.String.
The solution to this problem is simple. If the xref:System.Windows.Controls.Label is not set to a custom xref:System.Windows.Controls.ContentControl.ContentTemplate%2A value, replace the xref:System.Windows.Controls.Label with a xref:System.Windows.Controls.TextBlock and data bind its xref:System.Windows.Controls.TextBlock.Text%2A property to the source string.
| Data bound property | Update time (ms) |
|---|---|
| Label.Content | 835 |
| TextBlock.Text | 242 |
The xref:System.Windows.Documents.Hyperlink object is an inline-level flow content element that allows you to host hyperlinks within the flow content.
You can optimize the use of multiple xref:System.Windows.Documents.Hyperlink elements by grouping them together within the same xref:System.Windows.Controls.TextBlock. This helps to minimize the number of objects you create in your application. For example, you may want to display multiple hyperlinks, such as the following:
MSN Home | My MSN
The following markup example shows multiple xref:System.Windows.Controls.TextBlock elements used to display the hyperlinks:
[!code-xamlPerformance#PerformanceSnippet9]
The following markup example shows a more efficient way of displaying the hyperlinks, this time, using a single xref:System.Windows.Controls.TextBlock:
[!code-xamlPerformance#PerformanceSnippet10]
A xref:System.Windows.TextDecoration object is a visual ornamentation that you can add to text; however, it can be performance intensive to instantiate. If you make extensive use of xref:System.Windows.Documents.Hyperlink elements, consider showing an underline only when triggering an event, such as the xref:System.Windows.ContentElement.MouseEnter event. For more information, see Specify Whether a Hyperlink is Underlined.
The following image shows how the MouseEnter event triggers the underlined hyperlink:
The following markup sample shows a xref:System.Windows.Documents.Hyperlink defined with and without an underline:
[!code-xamlPerformance#PerformanceSnippet11]
The following table shows the performance cost of displaying 1000 xref:System.Windows.Documents.Hyperlink elements with and without an underline.
| Hyperlink | Creation time (ms) | Render time (ms) |
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| With underline | 289 | 1130 |
| Without underline | 299 | 776 |
WPF provides rich text formatting services, such as automatic hyphenations. These services may impact application performance and should only be used when needed.
Automatic hyphenation finds hyphen breakpoints for lines of text, and allows additional break positions for lines in xref:System.Windows.Controls.TextBlock and xref:System.Windows.Documents.FlowDocument objects. By default, the automatic hyphenation feature is disabled in these objects. You can enable this feature by setting the object's IsHyphenationEnabled property to true. However, enabling this feature causes WPF to initiate Component Object Model (COM) interoperability, which can impact application performance. It is recommended that you do not use automatic hyphenation unless you need it.
A xref:System.Windows.Documents.Figure element represents a portion of flow content that can be absolutely-positioned within a page of content. In some cases, a xref:System.Windows.Documents.Figure may cause an entire page to automatically reformat if its position collides with content that has already been laid-out. You can minimize the possibility of unnecessary reformatting by either grouping xref:System.Windows.Documents.Figure elements next to each other, or declaring them near the top of content in a fixed page size scenario.
The optimal paragraph feature of the xref:System.Windows.Documents.FlowDocument object lays out paragraphs so that white space is distributed as evenly as possible. By default, the optimal paragraph feature is disabled. You can enable this feature by setting the object's xref:System.Windows.Documents.FlowDocument.IsOptimalParagraphEnabled%2A property to true. However, enabling this feature impacts application performance. It is recommended that you do not use the optimal paragraph feature unless you need it.