Weird behaviour with Qml (transparent background)

uncore

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

KH-219Design

(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!)

jeremy_k

@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.

J.Hilk

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

uncore

@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

J.Hilk

@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:

but that comes with missing menu bar and stuff