Created attachment 122683 [details]
Graphical glitches

SUMMARY
Breeze Window buttons present graphical glitches when hovered making certain parts translucent, this glitch happens when the GPU (Intel HD 4400 in my case) is stressed in some way like playing fullHD video or another GPU intensive task

STEPS TO REPRODUCE
1. stress the GPU in some way (to cause FPS drops on Kwin)
2. hover the title bar buttons

OBSERVED RESULT
Graphical glitches are noticed around the window buttons

EXPECTED RESULT
Breeze buttons should render correctly upon hover

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 4.19 (Manjaro), also tested on KDE Neon live USB
(available in About System)
KDE Plasma Version: 5.16.5
KDE Frameworks Version: 5.61
Qt Version: 5.13.1

ADDITIONAL INFORMATION
This glitch also happens in QT 5.12 and older version of plasma and frameworks, It might be affecting only Intel GPUs but I can't test because I don't have newer/older intel GPUs and Nvidia/AMD GPUs.

WORKAROUNDS TESTED
Tried using the Intel driver in SNA/UXA and DRI2/DRI3 settings, tearfree ON/OFF to no avail
Tried using the modesetting driver, same results
This glitch also happens with window decorations fork like SierraBreeze and SierraBreezeEnhanced
Aurorae window decorations are unaffected by this bug