// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
//
//
// Contents: Text source callback methods
//
// Spec: Text Formatting API.doc
//
//
namespace System.Windows.Media.TextFormatting
{
/// <summary>
/// The client provides a concrete implementation of the abstract
/// TextSource class in order to provide both character data and
/// formatting properties to the text formatting engine.
///
/// All access to text in the TextSource is through the GetTextRun
/// method which is designed to allow the client to virtualize text
/// in any way it chooses.
/// </summary>
public abstract class TextSource
{
/// <summary>
/// TextFormatter to get a text run started at specified text source position
/// </summary>
/// <param name="textSourceCharacterIndex">character index to specify where in the source text the fetch is to start.</param>
/// <returns>text run corresponding to textSourceCharacterIndex.</returns>
public abstract TextRun GetTextRun(
int textSourceCharacterIndex
);
/// <summary>
/// TextFormatter to get text span immediately before specified text source position.
/// </summary>
/// <param name="textSourceCharacterIndexLimit">character index to specify where in the source text the text retrieval stops.</param>
/// <returns>text span immediately before the specify text source character index.</returns>
/// <remarks>
/// Return empty CharacterBufferRange in the text span if the text span immediately before the
/// specified position doesn't contain any text (such as inline object or hidden run).
/// Return a zero length TextSpan if there is nothing preceding the specified position.
/// </remarks>
public abstract TextSpan<CultureSpecificCharacterBufferRange> GetPrecedingText(
int textSourceCharacterIndexLimit
);
/// <summary>
/// TextFormatter to map a text source character index to a text effect character index
/// </summary>
/// <param name="textSourceCharacterIndex"> text source character index </param>
/// <returns> the text effect index corresponding to the text source character index </returns>
public abstract int GetTextEffectCharacterIndexFromTextSourceCharacterIndex(
int textSourceCharacterIndex
);
/// <summary>
/// PixelsPerDip at which the text should be rendered. Any class which extends TextSource should update
/// this property whenever DPI changes for a Per Monitor DPI Aware Application.
/// </summary>
public double PixelsPerDip
{
get { return _pixelsPerDip; }
set { _pixelsPerDip = value; }
}
private double _pixelsPerDip = MS.Internal.FontCache.Util.PixelsPerDip;
}
}
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