<![CDATA[Weird behaviour with Qml (transparent background)]]>I am trying to achieve a transparent background in Qml for Win11 mica effect but for some reason the app starts with a white background and as i resize the window it becomes transparent what am i doing wrong ?

Qml :

import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Controls.Universal 2.12

import QtQml 2.12

ApplicationWindow {
    visible: true
    color: "transparent"
    width: 640
    height: 480

    Button {
        id: btn
        text: "Button"
        anchors.centerIn: parent
    }
}

Win11 , Qt 6.8.3 , also happens on Qt6.9.3

You can clone to reproduce,
https://github.com/uncor3/qml-bug

bug.gif

]]>https://forum.qt.io/topic/164583/weird-behaviour-with-qml-transparent-backgroundRSS for NodeWed, 21 Oct 2026 07:22:23 GMTMon, 20 Apr 2026 14:17:51 GMT60<![CDATA[Reply to Weird behaviour with Qml (transparent background) on Tue, 21 Apr 2026 13:54:10 GMT]]>@uncore the actual problem is a false assumption. The black you see is not the transparent background after resize. It's just not rendered.

I don't know if you can actually get a normal ApplicationWindow with only a transparent background.

The Only way I know is via the QtFramelessWindowHint:

20d60691-52f3-4b4a-b1ed-591465ed7d0d-image.png

but that comes with missing menu bar and stuff

]]>https://forum.qt.io/post/837913https://forum.qt.io/post/837913Tue, 21 Apr 2026 13:54:10 GMT<![CDATA[Reply to Weird behaviour with Qml (transparent background) on Tue, 21 Apr 2026 13:11:17 GMT]]>@J.Hilk Didn't work. I actually tried forcing a rerender from both C++ and Qml side before but didn't work. Also this doesn't have anything to do with the Mica effect even i disable it the behavior is the same, starts with a white background then as i resize, it becomes transparent. Just tried with Qt 6.11.0 same result

]]>https://forum.qt.io/post/837912https://forum.qt.io/post/837912Tue, 21 Apr 2026 13:11:17 GMT<![CDATA[Reply to Weird behaviour with Qml (transparent background) on Tue, 21 Apr 2026 05:45:26 GMT]]>Try the following:

ApplicationWindow {
    id: rootWindowd
    visible: false
    color: "transparent"
    width: 640
    height: 480

    Component.onCompleted: rootWindowd.visible = true

    Button {
        id: btn
        text: "Button"
        anchors.centerIn: parent
    }
}

that should force a redraw after everything is finished/initialized

or

function forceRedraw() {
        rootWindowd.contentItem.update()
    }

If this works, than I would consider it a bug in the framework and you should open a bug report

]]>https://forum.qt.io/post/837903https://forum.qt.io/post/837903Tue, 21 Apr 2026 05:45:26 GMT<![CDATA[Reply to Weird behaviour with Qml (transparent background) on Mon, 20 Apr 2026 18:48:22 GMT]]>@KH-219Design said in Weird behaviour with Qml (transparent background):

ApplicationWindow {


  flags: Qt.WA_TranslucentBackground
  color: "transparent"

"WA" is short for WidgetAttribute, while Window.flags is expecting a combination of WindowFlags.

]]>https://forum.qt.io/post/837893https://forum.qt.io/post/837893Mon, 20 Apr 2026 18:48:22 GMT<![CDATA[Reply to Weird behaviour with Qml (transparent background) on Mon, 20 Apr 2026 18:52:52 GMT]]>(At least in Qt 5, I think the following was needed. Not sure in Qt6)

Does it help if you try this flags setting?

ApplicationWindow {


  flags: Qt.WA_TranslucentBackground // or perhaps not. (see correction below)
  color: "transparent"

UPDATE: whatever I was remembering or mis-rembering from Qt5 days, @jeremy_k has pointed out that I must be mistaken (and I concur).

(I didn't want to merely delete this comment, because when I come across "this post deleted" I always assume there was some weird spam initially, and that is not what this was!)

]]>https://forum.qt.io/post/837889https://forum.qt.io/post/837889Mon, 20 Apr 2026 18:52:52 GMT