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What does MergeAlpha option do?

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T O P I C R E V I E W
mouser	Posted - Feb 20 2013 : 08:55:59 I'm having trouble understanding the MergeAlpha parameter that is used in a few functions, including DrawObjectsToBitmap. The actual problem I'm having is I have an object on top of a 100% transparent background, and when I DrawObjectsToBitmap, the resulting bitmap still has 100% transparency and so the objects are invisible. So I guess what I'm ultimately looking for is a way to draw the objects to a background and "combine" in a reasonable way the transparency of the original background with the transparency of the objects being drawn onto it. I can think of some laborious multiple step masking methods to do that if there is no easy way in ImageEn -- and if someone knows an easier way I'd love to hear. But I'd still like to understand with the MergeAlpha option does as it's not clear to me. Thanks!
6 L A T E S T R E P L I E S (Newest First)
mouser	Posted - Feb 22 2013 : 13:07:40 Hi Fabrizio, I originally tried using CopyObjectsToBack, and it didn't work right -- however I cannot remember in what fashion it wasn't doing what I expected, and it may have been an error on my part. Nevertheless, I am quite certain that I have fixed a few bugs in the ImageEn code related to this stuff -- I will email you my fixes (i've actually made some other "improvement" so it will be up to you what you want to keep). ImageEn is a wonderful library.
fab	Posted - Feb 22 2013 : 03:29:24 Dear Mouser, it seems that the topic at: http://www.imageen.com/ieforum/topic.asp?TOPIC_ID=283 describes a different problem. In fact, using current version, now you can do: ImageEnVect1.IEBitmap.AlphaChannel.Fill(128); ImageEnVect1.AddNewObject(iekBox, Rect(10, 10, 100, 100), clRed); ImageEnVect1.CopyObjectsToBack(); ImageEnVect1.RemoveAllObjects(); ImageEnVect1.Update(); The box is displayed correctly, even if the background has 128 (50%) transparency.
w2m	Posted - Feb 20 2013 : 15:09:22 Send your fixes directly to Fabrizio: support@hicomponents.com William Miller Email: w2m@frontiernet.net EBook: http://www.imageen.com/ebook/ Apprehend: http://www.frontiernet.net/~w2m/index.html
mouser	Posted - Feb 20 2013 : 14:04:18 Ok i've patched the imageen code in a couple of places to fix a few bugs responsible for alpha mergeing not working. I've exchanged emails with Fabrizio a few times -- what's the best way to communicate some fixes?
mouser	Posted - Feb 20 2013 : 09:31:37 Last self-followup. The problem I appear to be having seems like it's the exact same bug reported here: http://www.imageen.com/ieforum/topic.asp?TOPIC_ID=283 Which was reported fixed by Fabrizio. As I am using the latest version (4.3) I wonder if in fact this is a bug which has not actually been fixed?
mouser	Posted - Feb 20 2013 : 09:22:38 A quick followup to explain the partial nature of my confusion. When using the TIEBitmap.MergeWithAlpha function to draw one partially transparent bitmap or layer onto a fully transparent (alpha 0) background, the result is what I expected -- which is that the resulting bitmap becomes non-transparent where the bitmap is drawn. But when using DrawObjectsToBitmap or CopyObjectsToBack with MergeAlpha option, the transparent backgrounds seem stay completely transparent, making the drawn objects completely invisible.