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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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AnswerRe: why doing win32 with c#? Pinmembertic8413:12 10 Jun '08  
GeneralVB.Net Pinmemberdawmail33322:47 24 Aug '07  
GeneralRe: VB.Net PinmemberDj Den4ik23:05 11 Feb '08  
GeneralRe: VB.Net PinmemberJason Newland19:31 25 Apr '12  
GeneralRe: VB.Net PinmemberJason Newland19:33 25 Apr '12  
GeneralGreat!!!!!!!!!!!!! Pinmembershp-coding7:44 9 Aug '07  
GeneralWay to add some controls Pinmemberihess4:17 30 Jul '07  
Add some controls to overlay transparent form and avoid refreshing it's content with common Refresh()/Invalidate() methods,
use UpdateLayeredWindow() instead. For correct controls rendering add code like
 
Bitmap temp_bmp = new Bitmap(bitmap);
foreach (Control ctrl in this.Controls)
{
ctrl.DrawToBitmap(temp_bmp, ctrl.Bounds);
}
hBitmap = temp_bmp.GetHbitmap(Color.FromArgb(0)); // grab a GDI handle from this GDI+ bitmap
 
to the PerPixelAlphaForm::SetBitmap() method. Every System.Windows.Forms controlhas method DrawToBitmap().
 
Actually, i used this way to render simple controls - labels, i don't know would it work with more complex
user controls, but i can't see why it should not Smile | :)

GeneralRe: Way to add some controls [modified] PinmemberSp3cial8:12 24 Aug '08  
GeneralRe: Way to add some controls [modified] PinmemberLatencyXXX23:21 23 Jan '11  
GeneralHelp Pinmembergsampath20:15 28 May '07  
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  
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  

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