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Details

Type: Bug
Resolution: Done
Priority: P1: Critical
Fix Version/s: 5.4.0 Beta
Affects Version/s: 5.4.0
Component/s: Quick: Other
Labels:
- qtquickcanvas

Commits:
c2706491906c053f5d38ddc0558a993bbf7cfd3e

Description

The following piece of QML work fine with Qt 5.3. The canvas item is blue and becomes blue again when the window is hidden and shown. When I use the same QML with the current state of Qt 5.4 the canvas is cleared on hiding and even cannot be painted to anymore when the window is shown again. It seems the context gets silently destroyed and isn't recreated later.

import QtQuick 2.2
import QtQuick.Window 2.1

Window {
    id: root
    visible: true
    width: 360
    height: 360

    Timer {
        repeat: true
        interval: 2000
        running: true
        onTriggered: {
            if (!root.visible) {
                root.show();
                //canvas.requestPaint(); <- triggers the "context dead" message on 5.4 but otherwise makes no difference
            } else {
                root.hide();
            }
        }
    }

    Canvas {
        id: canvas
        anchors.fill: parent
        contextType: "2d"
        onPaint: {
            if (context === null) {
                console.log("context is dead");
                return; // canvas isn't ready
            }

            context.reset();
            context.fillStyle = "blue";
            context.fillRect(0, 0, width, height);
        }
    }
}