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Clipping a Layered Window

Posted on 2006-06-30
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Last Modified: 2013-11-20
I have a layered pop-up window which contains several child dialogs.  the children should not be of concern to this question.  The outer corners of the pop-up are rounded, I have been using standard windows clipping regions to clip them however they produc a somewhat undesired jagged edge (no anti-aliasing).  If I make the region big enough to show the anti-aliased corner I get a crappy border around the pop-up (and you can still see the pixelation in it).  It is my understanding that the color-key of a layered window defines a color that will not be rendered to the desktop (transparent).  

I use SetLayeredWindowAttributes() to fade the popup in and out.  This works very well, so the function calls are being made.

In OnPaint(), I use GDI+ Graphics::Clear() to set the entire background to the desired 'transparent' color, I then procede to draw the pop-ups frame and interior.  But when it's all done, the transparent color is not very transparent (doesn't work).

// initial set layered window in the override of CreateEx() (after everything is created and verified)
// dont mind the '0' alpha, the pop-up initially fades in
SetLayeredWindowAttributes(RGB(0,0,255),0,LWA_COLORKEY|LWA_ALPHA);

So... ... How do I get my pop-up edges 'smoothly' transparent?

Thank you in advance.
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Question by:r2far
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mahesh1402 earned 300 total points
ID: 17019336
>>How do I get my pop-up edges 'smoothly' transparent?

UpdateLayeredWindow() has the additional advantage that the image defining the window shape can have per-pixel transparency.  Each pixel has an alpha value of 0-255, from total transparency (invisible) to total opacity..

UpdateLayeredWindow() allows you to gradually make the  edge of the window more and more transparent, as you move toward the edge.  This lets the edge blend into the background, no matter if the background is light or dark.  The edge is thus very smooth and non-pixellated.

Have a look at this article :
Per Pixel Alpha Blend : http://www.codeproject.com/gdi/pxalphablend.asp

-MAHESH
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Expert Comment

by:mahesh1402
ID: 17019363
I think article above at codeproject with src is exactly what you are looking for..use UpdateLayeredWindow() and check.

-MAHESH
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