[Okular-devel] Review Request 125313: Presentation: don't darken the image in the middle of the fade transition

[Arseniy Lartsev]

> On Oct. 14, 2015, 10:20 p.m., Albert Astals Cid wrote:
> > If you don't decreade the opacity of the original image it is not a fade though, is it?

I'd say fade transition between a pixel with value A and a pixel with value B (value being either of the color components) is C(t) = A * (1-t/T) + B * t/T, where T is the transition duration.

Which is what one gets from a pixel with value B and opacity t/T on top of a pixel with value A and opacity 1, according to color compositing formulas (found for example [here](https://www.cs.princeton.edu/courses/archive/fall00/cs426/papers/smith95a.pdf) or [here](https://en.wikipedia.org/wiki/Alpha_compositing#Description)).


- Arseniy


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On Sept. 27, 2015, 7:38 p.m., Arseniy Lartsev wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/125313/
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> 
> (Updated Sept. 27, 2015, 7:38 p.m.)
> 
> 
> Review request for Okular.
> 
> 
> Bugs: 352877
>     http://bugs.kde.org/show_bug.cgi?id=352877
> 
> 
> Repository: okular
> 
> 
> Description
> -------
> 
> Right in the middle of the fade transition, the previous and the next slide are painted each with 50% opacity on top of black background. This means that the black background will be slightly visible through the slides, which it shouldn't be. I propose a patch to fix this.
> 
> 
> Diffs
> -----
> 
>   ui/presentationwidget.cpp 0d9a55d 
> 
> Diff: https://git.reviewboard.kde.org/r/125313/diff/
> 
> 
> Testing
> -------
> 
> Works for me.
> 
> 
> File Attachments
> ----------------
> 
> Test case (two blank pages, 0.5s long fade transition)
>   https://git.reviewboard.kde.org/media/uploaded/files/2015/09/27/7df41157-5884-4a29-b3ea-f3590b7bf831__blank_transition.pdf
> 
> 
> Thanks,
> 
> Arseniy Lartsev
> 
>

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