Per Pixel Alpha Blend in C#

• Download source code and sample application - 89 Kb

Introduction

This is a port of my other article from C++/MFC to C#/Windows Forms. The concept of creating a per-pixel-alpha blending window remains the same, the GDI function UpdateLayeredWindow.

What changed

• Image loading is handled by GDI+ classes (System.Drawing namespace).
• No need to pre-multiply the rgb channels with the alpha channel.
• No more support for PSP files. PNG file are the best choice.

Usage

To use this code you need to include PerPixelAlphaForm.cs file in your project, create a class that inherits from PerPixelAlphaForm, load a bitmap using System.DrawingImage.FromFile static method and then call the PerPixelAlphaForm.SetBitmap method.

The example source code is inside the main.cs file. In the source code you will also find the new ways of doing the old things, like, handling dropped files from windows explorer.

Installing & Building

1. Download and extract the source code of this article;
2. To build, run the build.bat file from command prompt;
3. Now, run the bin\main.exe and enjoy!

Changelog

31 May 2004

• Fix clipping problems by creating the form without borders.
• Move PerPixelAlphaForm class to PerPixelAlphaForm.cs file.

12 Feb 2002

• Initial version.

Do you have any question or comment? Contact me!