Image processor

Step-by-step tutorial

This tutorial will demonstrate how to create a simple "image editor" application (Image Processor), which uses collection of C# script files for image manipulations. "Type sharing" pattern in this tutorial is implemented with passing custom type between the script host and the actual script.

It is highly advisable to read the "Passing custom type..." section before starting this tutorial.

This tutorial as an example of balanced approach for implementing the script host application. This approach is based on the general script hosting concept described in the "Script hosting guideline" section.

Only the code, which logically belongs to the script hosting implementation will be discussed here. To accomplish this tutorial you will need to download ImageProcessor.zip file. Then extract the content of the zip file in the convenient location.

The host application for this tutorial comes in two flavors: C# script (imageprocessor.cs) and Visual Studio 2003 (VS7.1) project (content of extracted folder imageprocessor ). All code snippets in this tutorial are taken from the imageprocessor.cs script however they are applicable to the VS7.1 project to the same degree.

This tutorial demonstrates how to:

load and execute C# script file from the application
pass and retrieve custom type between the C# script and the host application

Firstly let's see the Image Processor action:

Open command prompt. Make sure current directory is the directory where content of ImageProcessor.zip is extracted.
Start Image Processor by executing the following command in command prompt:

csws imageprocessor

Output

The script will create and show the following dialog.

The right panel (script panel) contains names of the C# script files from the ImageProcessor/Scripts folder. These files contain some image manipulation routine. If you double-click on the item in a script list the corresponding script will be executed. Script execution means passing the image (left panel) to the script and retrieving it back with some modifications. This is the result of execution the "RedOff" script (it removes the red color component from every pixel in the image):

Code discussion

Application design considerations

The following are the rules that affect application design:

The valid script file is a file containing C# code with implementation of public class ImageEditorScript.
The class ImageEditorScript must have public static method: Image Modify (Image);

This is an example of a very simple class that implements rendering of watermark (Watermark.cs):

using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System;

public class ImageEditorScript
{
   public Image Modify(Image image)
   {
      Bitmap newBitmap = new Bitmap(image.Width, image.Height, PixelFormat.Format32bppArgb);

      using (Graphics g = Graphics.FromImage(newBitmap))
      {
         g.DrawImage(image, 0.0f, 0.0f); //draw original image
         g.DrawString( "Watermark",
                       new Font("Arial", 30),
                       new SolidBrush(Color.FromArgb(90, 255, 255, 255)), 20, 20);
      }
      return newBitmap;
   }
}

The host application contains class Script which manages compiling and loading the script file. It loads the script file by using CSScript.LoadCode() method.

CSScript.Load(file, null, true);

Class Script has the method Modify, which "borrows" the implementation from the associated script file. This is how it is used in the
host:

public Image Modify(Image image)
{
var Modify = new CSScript.Load(file, null, true)
.GetStaticMethod("*.Modify", image); //or just GetStaticMethod()

return (Image)Modify(image);
}

Note that it is possible to cache compiled script in this class (Script) however CSScript can do it for you. Regardless how many times you call CSScript.Load() it compiles script only if it was changed since the last execution.

Image Processor

Step-by-step tutorial

Output

Code discussion

See Also