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First Posted 11 Feb 2002
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Per Pixel Alpha Blend in C#

By | 3 Jun 2004 | Article
Demonstrates how to create per pixel alpha blending windows

Preview of the per pixel alpha blend effect

Preview of the per pixel alpha blend effect

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!

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Rui Lopes

Web Developer

Portugal Portugal

Member



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GeneralImage problem Pinmemberdarb212:57 20 Apr '07  
GeneralRe: Image problem PinmemberDaryl Fish14:58 15 Jan '08  
GeneralProblem when changing the form parent to desktop with dual-monitoring [modified] PinmemberPim-Pom1:59 7 Oct '06  
GeneralNice example, but... Pinmembermoebiusproject9:35 12 Sep '06  
GeneralRe: Nice example, but... PinmemberTung Nguyen17:37 15 Apr '07  
GeneralRe: Nice example, but... Pinmembertic8413:14 10 Jun '08  
GeneralProblem in design mode PinmemberCapt'N Stabbin'19:09 12 Jul '06  
Hi,
 
This is some great code, I pissed around for ages trying to get this working before I stumbled across this page.
 
Now, it works just fine, the only thing is that forms descended from a PerPixelAlphaForm don't work in the VS2005 designer, you just get:
 
One or more errors encountered while loading the designer. The errors are listed below. Some errors can be fixed by rebuilding your project, while others may require code changes.
 
Error creating window handle.
 
This doesn't stop the project from building or running though, but it's a pain not being able to use the designer.
 
Any ideas?
 
Thanks!

GeneralRe: Problem in design mode PinmemberODaniell0:52 3 Aug '06  
GeneralRe: Problem in design mode PinmemberMember 42028004:50 19 May '09  
QuestionHow Can I Add Controls? Pinmemberranzige16:32 2 Dec '05  
AnswerRe: How Can I Add Controls? Pinmemberwang.songqing20:16 20 Jun '06  
Generalrecognition Pinmemberamir mortazavi18:36 26 Jan '05  
QuestionCan this be done in DirectX? Pinmember#teve2:58 27 Dec '04  
GeneralNice but... Pinmemberrioman5:05 6 Sep '04  
GeneralRe: Nice but... PinmemberRui Godinho Lopes13:31 8 Sep '04  
GeneralRe: Nice but... Pinmemberrioman3:56 9 Sep '04  
GeneralRe: Nice but... PinsussAnonymous1:34 5 Oct '04  
GeneralRe: Nice but... Pinmembergreggman19:22 24 Jan '05  
GeneralRe: Nice but... [modified] PinmemberGreg Ellis6:45 20 Oct '06  
GeneralAlpha Blend as a background Pinmembergozza112:14 2 Jul '04  
Generalmulti transparent forms Pinmembermazro37:31 28 Jun '04  
GeneralCreating Slices of an Image PinmemberSameers (theAngrycodeR )5:55 9 Jun '04  
GeneralClipping Problem Pinmembergarythemann11:51 5 Apr '04  
GeneralRe: Clipping Problem PinmemberTom Guinther13:00 7 May '04  
GeneralRe: Clipping Problem Pinmemberj2demelo17:30 30 May '04  

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