Bug 505207

Summary: Directional Blur does not extend beyond boundaries.
Product: [Applications] kdenlive Reporter: nuxttux
Component: Video Effects & TransitionsAssignee: Jean-Baptiste Mardelle <jb>
Status: CONFIRMED ---    
Severity: normal CC: berndmj
Priority: NOR Keywords: triaged
Version First Reported In: 25.04.1   
Target Milestone: ---   
Platform: Flatpak   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description nuxttux 2025-06-04 14:32:47 UTC 
SUMMARY
When you apply Directional Blur to a clip (Title clips for example), the blur stays contained inside the visible pixels, blurring the alpha inwards instead of blurring the pixels outwards. It use to work properly prior to the latest update, before 25.04.

Here is what it looked like before, https://youtu.be/44ufamHGIgQ?si=n26tLWmWIJ8QQSuf&t=426
Video will start on example, (7:06).

STEPS TO REPRODUCE
1. Create Title clips, large, white text.
2. Place Title clip on timeline and add Directional Blur to it.
3. Increase the radius of Directional blur.

OBSERVED RESULT
The text itself won't blur, but rather the alpha will blur inwards on the text (Title clip).

EXPECTED RESULT
For the title clip text to blur entirely, like a smudge in the direction of the angle.
For the alpha to not be affected or seen as a black solid.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 6.13.0
Qt Version: 6.9.0

ADDITIONAL INFORMATION
This worked properly before in 24.X, the link provided has an example of how it worked before the latest update.
Comment 1 Bernd 2025-06-05 23:28:09 UTC 
I can confirm this behavior (25.04.1 Flatpak on Pop!_OS 22.04)

I also remember that blurring title clips had the issue of not blurring anything outside of the text. Arkengheist found out that adding a black box behind the text allowed the blur to happen properly. This workaround still works in 25.04.1 but then you need a composition with Cairo Affine Blend and blend mode Screen.
Interestingly enough, adding dblur to the title clip in the bin displays it properly in the clip monitor (but only if the background color is black; if set to any other color that is available, it doesn't work either) but not in the the project monitor when overlaying a clip in a track below.