Maps a portion of the index buffer into memory, so that indices can be written into it. see  IndexStream  . 
   Namespace:   Autodesk.Revit.DB.DirectContext3D  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 19.0.0.0 (19.0.0.405) 
  Since:  2017 
Syntax
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Parameters
- sizeInShortInts
-  Type:  System Int32  
 The size of the part of the buffer to be mapped, measured in short integers. Must be less than or equal to the size of the IndexBuffer
Exceptions
| Exception | Condition | 
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| Autodesk.Revit.Exceptions InvalidOperationException | This IndexBuffer is not available because Revit is not currently rendering. In general, this IndexBuffer must be used in the scope of the RenderScene() callback of IDirectContext3DServer. -or- Thrown if the buffer is smaller than sizeInShortInts. |