Capturing an image of the current AutoCAD document using .NET

This is a topic that has been addressed a few times on this blog, whether by posts that use the 3D graphics system to capture screenshots or the series of posts regarding the Screenshot Plugin of the Month from a few years ago. I thought it worth revisiting, though, as I noticed an API that I hadn’t used before and decided to put it through its paces.

The API is a simple one – Document.CapturePreviewImage() – and it’s been covered before on the AutoCAD DevBlog. But I thought I’d take some file-selection code from the Screenshot app and see whether it was possible to create a full-size screenshot of the current drawing window using it.

Here’s the C# implementation of a CPI command that uses the API to save a “preview” image that’s the same exact size as the document window.

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using System;
using System.Drawing.Imaging;
using System.IO;
 
namespace ListApplications
{
  public static class Extensions
  {
    // Return the image format to use for a particular filename
 
    public static ImageFormat GetFormat(this string filename)
    {
      // If all else fails, let's create a PNG
      // (might also choose to throw an exception)
 
      var imf = ImageFormat.Png;
      if (filename.Contains("."))
      {
        // Get the filename's extension (what follows the last ".")
 
        string ext = filename.Substring(filename.LastIndexOf(".") + 1);
 
        // Get the first three characters of the extension
 
        if (ext.Length > 3)
          ext = ext.Substring(0, 3);
 
        // Choose the format based on the extension (in lowercase)
 
        switch (ext.ToLower())
        {
          case "bmp":
            imf = ImageFormat.Bmp;
            break;
          case "gif":
            imf = ImageFormat.Gif;
            break;
          case "jpg":
            imf = ImageFormat.Jpeg;
            break;
          case "tif":
            imf = ImageFormat.Tiff;
            break;
          case "wmf":
            imf = ImageFormat.Wmf;
            break;
          default:
            imf = ImageFormat.Png;
            break;
        }
      }
      return imf;
    }
  }
 
  public class Commands
  {
    [CommandMethod("CPI")]
    static public void CreatePreviewImage()
    {
      var doc = Application.DocumentManager.MdiActiveDocument;
      if (doc == null) return;
 
      var ed = doc.Editor;
 
      // Select the filename and type for our output image
 
      var pofo = new PromptSaveFileOptions("\nSelect image location");
 
      pofo.Filter =
        "Bitmap (*.bmp)|*.bmp|GIF (*.gif)|*.gif|JPEG (*.jpg)|*.jpg|" +
        "PNG (*.png)|*.png|TIFF (*.tif)|*.tif";
 
      // Set the default save location to be that of the current drawing
 
      string fn = doc.Database.Filename;
      if (fn.Contains("."))
      {
        int extIdx = fn.LastIndexOf(".");
        if (fn.Substring(extIdx + 1) != "dwt" && fn.Contains("\\"))
        {
          pofo.InitialDirectory = Path.GetDirectoryName(doc.Database.Filename);
        }
      }
 
      var pfnr = ed.GetFileNameForSave(pofo);
      if (pfnr.Status != PromptStatus.OK)
        return;
 
      var outFile = pfnr.StringResult;
 
      // Get the size of the document and capture the preview at that size
 
      var size = doc.Window.DeviceIndependentSize;
      using (
        var bmp =
          doc.CapturePreviewImage(
            Convert.ToUInt32(size.Width), Convert.ToUInt32(size.Height)
          )
      )
      {
        // Save the file with the format derived from the filename
 
        bmp.Save(outFile, outFile.GetFormat());
      }
    }
  }
}
 