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<div class="moz-cite-prefix">On 13/01/2026 19:07, Dmitry Kazakov
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAEkBSfX4hAYsEcHEnAQV3j1raxgzzfDGEADgqyM1osFfiL7fSQ@mail.gmail.com">
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<div>Hi, all!</div>
<div><br>
</div>
<div>If someone might be interested in that, I did a bit of
research on implementing a way of fetching screen's SDR
brightness level in Qt's QScreen implementation on Windows.
This value is configured by the user in the display settings,
so the application needs this value to be able to blend the
GUI elements on the HDR canvas.</div>
<div><br>
</div>
<div>Here is the draft patch:</div>
<div><a
href="https://invent.kde.org/dkazakov/qtbase/-/commit/b401b32e3eb2616087ca9614df18959673c05e5a"
moz-do-not-send="true" class="moz-txt-link-freetext">https://invent.kde.org/dkazakov/qtbase/-/commit/b401b32e3eb2616087ca9614df18959673c05e5a</a></div>
<div><br>
</div>
<div>Current limitations:</div>
<div><br>
</div>
<div>1) The feature is implemented on Windows only. It is
technically possible to implement that on Wayland, but this
draft doesn't address that.<br>
<br>
2) QScreen::sdrBrightnessLevelChanged() signal is
**NOT** delivered when the user actually changes the SDR
brightness preference. There seems to be no WinAPI
message delivered when this setting is changed. At least
nothing I could see in the docs or event stream dumps. Id you
know some details about that, please yell! :)<br>
</div>
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</blockquote>
<p>I checked what Chrome/Chromium does (both the code and the actual
behaviour), and it seems to only refresh the SDR brightness value
on receiving `WM_ACTIVATEAPP`, so it seems even Chromium devs
haven't found a way to get notified of the SDR brightness
changing, or perhaps they just consider this good enough.</p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:CAEkBSfX4hAYsEcHEnAQV3j1raxgzzfDGEADgqyM1osFfiL7fSQ@mail.gmail.com">
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<div><br>
Though the signal is delivered when the user toggles SDR and
HDR modes of the screen. It makes Windows to deliver
WM_DISPLAYCHANGE, which is handled by QWindowsScreenManager
properly.</div>
<div><br>
</div>
<div>--</div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">Dmitry Kazakov</div>
</div>
</blockquote>
Alvin Wong
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