Unsolved QtCharts Does not support Alpha?

[antiocles]

Does the chart module not support use of alpha in color definitions?

I was attempting to remove the border of a pie slice. Setting border to 0 does not do it. Nor does setting the border color to transparent. I then discovered that any color definitions seem to just silently ignore alpha channel. I even went so far as to link into some C++ code to manually control the brushes/pens/colors without going through QML and that does not work either.

I suspected the more limited openGL might be the issue, but pie would not be supported by that. I tried other series types (line, bar, etc) and all behave the same.

Thoughts?

[fcarney]

Can you make a minimal qml app that reproduces the problem with nothing else in that app? Then share your code so we have something to look at?

[antiocles]

Hello,

As I made my minimal application, I discovered that it does work with alpha in colors as expected BUT turning on animations causes it to ignore the alpha channel for the animated items...

I opened the qmlchart example, and modify View1.qml:

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the Qt Charts module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:GPL$
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** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
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** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
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****************************************************************************/

//![2]
import QtQuick 2.0
//![2]
import QtCharts 2.0

Item {
    anchors.fill: parent
    property variant othersSlice: 0

    //Just to give a background to see transparency easier...
    Image {
        id: image
        anchors.fill: parent
        source: "http://www.google.com/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png"
        fillMode: Image.Stretch
        opacity: 0.3
    }

    //![1]
    ChartView {
        id: chart
        title: "Top-5 car brand shares in Finland"
        anchors.fill: parent
        legend.alignment: Qt.AlignBottom
        antialiasing: true
        backgroundColor: "#0100FF00"
        animationOptions: ChartView.AllAnimations //<--kills alpha channel if have animations on

        PieSeries {
            id: pieSeries
            holeSize: .3
            PieSlice { label: "Volkswagen"; value: 25; color: "#50FF0000" }
            PieSlice { label: "Toyota"; value: 10.9;  color: "#3000FF00"}
            PieSlice { label: "Ford"; value: 8.6; color: "#800000FF" }
            PieSlice { label: "Skoda"; value: 8.2 }
            PieSlice { label: "Volvo"; value: 6.8 }
        }
    }

    Component.onCompleted: {
        // You can also manipulate slices dynamically, like append a slice or set a slice exploded
        othersSlice = pieSeries.append("Others", 52.0);
        pieSeries.find("Volkswagen").exploded = true;
    }
    //![1]
}

And then the alpha is being ignored. I know working with transparency will be a bit more costly, but I definitely did not anticipate total disabling. Is this intended? Or a bug I should be reporting?

This is on qt 5.14.2, mac, but seems to do the same other places i have looked at (not 5.15 yet...)

[fcarney]

I played with this a bit. It looks like once animations are enabled you lose transparency. I don't see anything in the docs about this either. So either it is an optimization or a bug. Since you have a simple reproducible example I would submit a bug.