Shape Path Translucent Overdraw Problem (GL specific?)

matthew.kuiash

Hi everybody. Long time no post - long story.

I've got stuck with what I think seems to be a triangle overdraw problem with shapes.

Firstly - Qt 5.11 on MacOS 10.13.4. iMac 5K later 2014. Also observed on iPad Pro.

Secondly here's the code.

// (C) kindid.co.uk 2018

import QtQuick 2.10
import QtQuick.Window 2.10
import QtQuick.Shapes 1.11

Window {
    id: root
    visible: true
    width: 320
    height: 320
    title: qsTr("KD Button Test")
    Shape {
        id: shape
        property int radius: 40
        anchors.fill: parent
        anchors.margins: 20
        ShapePath {
            strokeWidth: 30
            strokeColor: Qt.rgba(0.5,0.5,1,0.5)
            fillColor: Qt.rgba(0,0,1,1)
            startX: shape.radius
            startY: 0
            PathArc {
                x: 0
                y: shape.radius
                radiusX: shape.radius
                radiusY: shape.radius
                direction: PathArc.Counterclockwise
            }
            PathLine {
                x: 0
                y: shape.height - shape.radius
            }
            PathArc {
                x: shape.radius
                y: shape.height
                radiusX: shape.radius
                radiusY: shape.radius
                direction: PathArc.Counterclockwise
            }
            PathLine {
                x: shape.width - shape.radius
                y: shape.height
            }
            PathArc {
                x: shape.width
                y: shape.height - shape.radius
                radiusX: shape.radius
                radiusY: shape.radius
                direction: PathArc.Counterclockwise
            }
            PathLine {
                x: shape.width
                y: shape.radius
            }
            PathArc {
                x: shape.width - shape.radius
                y: 0
                radiusX: shape.radius
                radiusY: shape.radius
                direction: PathArc.Counterclockwise
            }
            PathLine {
                x: shape.radius
                y: 0
            }
        }
    }
}

Thirdly - Here's what that renders - notice the glitches where the arcs and lines meet. My supposition is that those pixels are being drawn twice - hence the colour is wrong - it's been blended with itself as it were. I found similar things in my own renderers before.

Setting QT_QUICK_BACKEND to "software" and running again I get a correct result (however, this is not really and option for me)

Any pointers?