source: branches/2645_ContextAlgorithms/HeuristicLab.ExtLibs/HeuristicLab.AvalonEdit/5.0.1/AvalonEdit-5.0.1/Rendering/VisualLineElementGenerator.cs

// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
// 
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// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;

namespace ICSharpCode.AvalonEdit.Rendering
{
  /// <summary>
  /// Abstract base class for generators that produce new visual line elements.
  /// </summary>
  public abstract class VisualLineElementGenerator
  {
    /// <summary>
    /// Gets the text run construction context.
    /// </summary>
    protected ITextRunConstructionContext CurrentContext { get; private set; }
    
    /// <summary>
    /// Initializes the generator for the <see cref="ITextRunConstructionContext"/>
    /// </summary>
    public virtual void StartGeneration(ITextRunConstructionContext context)
    {
      if (context == null)
        throw new ArgumentNullException("context");
      this.CurrentContext = context;
    }
    
    /// <summary>
    /// De-initializes the generator.
    /// </summary>
    public virtual void FinishGeneration()
    {
      this.CurrentContext = null;
    }
    
    /// <summary>
    /// Should only be used by VisualLine.ConstructVisualElements.
    /// </summary>
    internal int cachedInterest;
    
    /// <summary>
    /// Gets the first offset >= startOffset where the generator wants to construct an element.
    /// Return -1 to signal no interest.
    /// </summary>
    public abstract int GetFirstInterestedOffset(int startOffset);
    
    /// <summary>
    /// Constructs an element at the specified offset.
    /// May return null if no element should be constructed.
    /// </summary>
    /// <remarks>
    /// Avoid signalling interest and then building no element by returning null - doing so
    /// causes the generated <see cref="VisualLineText"/> elements to be unnecessarily split
    /// at the position where you signalled interest.
    /// </remarks>
    public abstract VisualLineElement ConstructElement(int offset);
  }
  
  internal interface IBuiltinElementGenerator
  {
    void FetchOptions(TextEditorOptions options);
  }
}