今天无意中发现一个叫 Paint.NET 的开源项目，其功能十分强大，界面模仿 Photoshop，是学习 GDI+ 的好例子。

Overview

Paint.NET is image and photo manipulation software designed to be used on computers that run Windows XP or 2000. Paint.NET is jointly developed at Washington State University with additional help from Microsoft, and is meant to be a free replacement for the MS Paint software that comes with all Windows operating systems. The programming language used to create Paint.NET is C#, with GDI+ extensions. 
Paint.NET has many of the powerful features that expensive commercial applications have, including the ability to use layers. This is the second semester that Paint.NET has been a project at Washington State University, and we have the goal of adding as much functionality as expensive commercial applications provide, but of course, for free! In the spirit of all this freedom, we welcome any suggestions, as well as provide the source code free of charge for anyone who wishes to tinker with it. Please explore this website, download the software and try out many of the things you would do on those expensive commercial applications.

Features

Graphic Design

• Layers
• History Window
• Various Brushes
• Special Effects

Photography

• Red Eye Removal
• Layer Touch ups
• Ability to scan pictures directly into Paint.NET in Windows XP
• Crop Tool

Web Design

• Save JPEGS in various file sizes
• Full PNG transparency support

Full PNG transparent background support.

Work with layers, a powerful feature usually found only on expensive commercial applications

All of the windows inside Paint.NET become transparent when moved over the image! You can use this feature to make your effects more precise.

Unlimited history allows you to go way back to fix any mistakes. As long as you have memory, you have more history!

Use one of the many effects included in Paint.NET v2.0 to make your image stand out . Even download additional effects plugins !

Use many different fonts in addition to all the layers, effects, and other cool tools

有兴趣的朋友可以到其官方网站了解更多的情况和下载源码。
http://www.eecs.wsu.edu/paint.net/