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Per Pixel Alpha Blend in C#

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3 Jun 20041 min read 602.8K   19.4K   191   115
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 new ways of doing 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

31st May, 2004

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

12th February, 2002

  • Initial version

Do you have any question or comment? Please leave a note below.

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.


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Comments and Discussions

 
GeneralRe: Problem in design mode Pin
sebastianlaskawiec19-May-09 4:50
sebastianlaskawiec19-May-09 4:50 
QuestionHow Can I Add Controls? Pin
ranzige2-Dec-05 16:32
ranzige2-Dec-05 16:32 
AnswerRe: How Can I Add Controls? Pin
wang.songqing20-Jun-06 20:16
wang.songqing20-Jun-06 20:16 
Generalrecognition Pin
amir mortazavi26-Jan-05 18:36
amir mortazavi26-Jan-05 18:36 
QuestionCan this be done in DirectX? Pin
#teve27-Dec-04 2:58
#teve27-Dec-04 2:58 
GeneralNice but... Pin
rioman6-Sep-04 5:05
rioman6-Sep-04 5:05 
GeneralRe: Nice but... Pin
Rui Lopes8-Sep-04 13:31
Rui Lopes8-Sep-04 13:31 
GeneralRe: Nice but... Pin
rioman9-Sep-04 3:56
rioman9-Sep-04 3:56 
Actualy i did, by seemlessly creating another form on top of yours with a transparency key. The later form works as a placeholder for every control. The result is close to perfect but with only one issue:
If the user clicks outside a control on the top form, it activates your form. I can't find a way to avoid mouse clicking getting the focus to your form.

I do try to catch the mouse click event but when I do so, it's already too late as the background form already got the focus.

There is also another strange behaviour to your form. I have a form that inherits from yours. If i set the "ShowInTaskBar" to false, it actualy hides the entire form!
The workaround I found is to set it to false directly in the PerPixelForm constructor.

Thank god, code-project and yourself I have the source code =P

Luis Ferrao
GeneralRe: Nice but... Pin
Anonymous5-Oct-04 1:34
Anonymous5-Oct-04 1:34 
GeneralRe: Nice but... Pin
greggman24-Jan-05 19:22
greggman24-Jan-05 19:22 
GeneralRe: Nice but... [modified] Pin
Greg Ellis20-Oct-06 6:45
Greg Ellis20-Oct-06 6:45 
GeneralAlpha Blend as a background Pin
gozza112-Jul-04 2:14
gozza112-Jul-04 2:14 
Generalmulti transparent forms Pin
mazro328-Jun-04 7:31
mazro328-Jun-04 7:31 
GeneralCreating Slices of an Image Pin
Sameers Javed9-Jun-04 5:55
Sameers Javed9-Jun-04 5:55 
GeneralClipping Problem Pin
Gary Mann5-Apr-04 11:51
Gary Mann5-Apr-04 11:51 
GeneralRe: Clipping Problem Pin
Tom Guinther7-May-04 13:00
Tom Guinther7-May-04 13:00 
GeneralRe: Clipping Problem Pin
j2demelo30-May-04 17:30
j2demelo30-May-04 17:30 
GeneralRe: Clipping Problem Pin
Rui Lopes31-May-04 1:51
Rui Lopes31-May-04 1:51 
QuestionCan not Hit it at Lasting Windows XP Updata & Windows 2003. Pin
wujingping2-Apr-04 5:21
wujingping2-Apr-04 5:21 
AnswerRe: Can not Hit it at Lasting Windows XP Updata & Windows 2003. Pin
Tom Guinther8-Jun-04 2:48
Tom Guinther8-Jun-04 2:48 
GeneralUsed your code Pin
joepardue24-Mar-04 7:40
joepardue24-Mar-04 7:40 
QuestionVB.NET Example? Pin
andrew|6-Dec-03 11:23
andrew|6-Dec-03 11:23 
AnswerRe: VB.NET Example? Pin
Steve Schaneville23-Dec-03 11:13
professionalSteve Schaneville23-Dec-03 11:13 
GeneralRe: VB.NET Example? Pin
thesleeper19-Jul-04 21:17
thesleeper19-Jul-04 21:17 
GeneralNice but superfluous Pin
lsauer2-Sep-03 7:15
lsauer2-Sep-03 7:15 

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