QtQuick DragHandler Lag

KenAppleby 0

With the QtQuick DragHandler there is a noticeable lag between the pointer motion and the target item translation. A rapid drag results in the drag target sliding across the screen to "catch up" with the pointer. A simple test of this is below. The lag is apparent on Windows and Android.

Is there a way to adjust this behaviour to reduce the lag? Or is this an unavoidable feature of QML?

import QtQuick 2

Window {
    id: window
    width: 640
    height: 480
    visible: true

    Rectangle {
        id: x
        width: 100
        height: 100
        color: "blue"
    }
    DragHandler {
        id: dragHandler
        target: x
    }
}

StudentScripter

@KenAppleby-0 Having the same issue as you have. Have you found a solution?

KenAppleby 0

@StudentScripter No, I haven't. But I think it must be possible to improve the performance. If you try the Qt positioning examples that use the QtQuick Map element the responsiveness to drag gestures is good. The Qt documentation states that Map uses OpenGL (ES) but I have not found a way to match the responsiveness of QtQuick Map even using OpenGL.

However, I find that a QGraphicsView with a QOpenGLWidget viewport performs really well on mobile platforms, even though some people in this forum claim that you can't use QWidgets on them.