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Image transistion

Posted on 2007-11-29
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Last Modified: 2013-12-26
Hi,

I wanted to make a simple image effect. I want a bitmp to fade to %100 transparency for example. I'm not sure how this would be done in a general sense. I'm working on win32.

I was thinking that I could have an image class with a member that represents opactiy:

    class FadeImage {
        Bitmap m_Img;
        double m_dOpacity = 100.0;
    };

When I want the image to fade, I can just call some method to initiate it, and keep generating WM_PAINT messages until it's done:

     void FadeImage::StartFade()
     {
          while (m_dOpacity != 0) {
               m_dOpacity--;
               Invalidate();
          }
     }

That would work, but the system will just block the user from doing much until the fade is done. I'm wondering how packages like flash do it. They can carry a fade out while still allowing mouse interaction. What's the general way to do something like this?

Thanks

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Question by:DJ_AM_Juicebox
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Jaime Olivares earned 2000 total points
ID: 20379285
you should use a Win32 timer. passing the object pointer. This will fire the timer event ever 'n' miliseconds, so you can repaint in every event.
Of course this will involve other task like kill timer when fade is done and check if window where you show the bitmap is still valid.
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Expert Comment

by:Jaime Olivares
ID: 20379297
A clock application would be a good example about using timer to repaint. Have a look to this one:
http://smallcode.weblogs.us/2006/04/11/things-are-not-as-easy-as-they-seem-writing-a-clock-application/
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Expert Comment

by:jkr
ID: 20379667
If you want transparency, probably using 'SetLayeredWindowAttributes()' (http://msdn2.microsoft.com/en-us/library/ms633540.aspx) is more what you are looking for. See also http://www.codeproject.com/w2k/trans.asp ("Transparency without Source Code")
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