[Libreoffice-bugs] [Bug 134213] Changed transparency handling in Draw breaks export to PNG of transparent objects over pictures with just default Layout layer, forces use of additional layer(s) for transparent shape(s)

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=134213

--- Comment #21 from mwtjunkmail at gmail.com ---
The loss of detail that I mentioned when a transparent element is placed over a
picture is a real phenomenon. 

I created a new template and used layers to use for transparent objects. One LO
draw page has a transparent object, the other does not, but otherwise they are
duplicates of each other.

I exported both LO draw pages as PNG, then opened both exported PNG files in
paint.net.

Paint.net reveals that what's happening is that the underlying image has a
transparency effect applied to it at the time of export (I say time of export,
because the transparency property of the object itself in LO Draw not modified,
it's still set to 0, so the only way it could have gotten transparent was
during the export process).

This https://i.imgur.com/QX6wNcF.png is a side-by-side comparison in paint.net
of the PNG exports of the two LO drawing pages. One  page has a transparent
object, the other does not. Again, I used layers this time, I didn't just put
everything on the layout layer like I've done prior to LO 7.0.


If you examine https://i.imgur.com/QX6wNcF.png, the red stripe on the right
actually spans the distance of the entire side-by-side comparison, in its on
paint.net layer in the comparison beneath the two exported PNG images. 

That red stripe is actually behind both pictures, but only shows up on the
right picture because a transparency effect has been inappropriately assigned
to the underlying image residing beneath the transparent object (that being the
Liberation Sans narrow text box).

That inappropriate transparency effect on the underlying image upon PNG export
is what's causing the loss of detail and blanching. 

I'll attach the LO Draw document that I used to demonstrate this as
transparency bug comparison.odg.

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