QPainter rotation angle draw lines，has some problem

import QtQuick 2.15

Canvas {
    id: control

    property real mLineCount: 360 * 2
    property real mRotation: 0

    onPaint: {
        var r = Math.min(width, height) / 2 - 2
        var ctx = getContext("2d")
        ctx.clearRect(0, 0, width, height)

        ctx.save()
        ctx.translate(width / 2, height / 2)
        ctx.strokeStyle = Qt.rgba(0.5, 0, 0, 1)
        ctx.lineWidth = 0.5 // + 1E-7
        // Qml default flat, qpainter default square
        // If not flat, multiple rotate will be uneven
        ctx.lineCap = "square"
        for (var i = 0; i < mLineCount; i++)
        {
            // If not save/restore, multiple rotate will be uneven
            ctx.save()
            ctx.rotate((mRotation + 360.0 / mLineCount * i) * Math.PI / 180.0)
            ctx.beginPath()
            ctx.moveTo(0, 0)
            ctx.lineTo(r, 0)
            ctx.stroke()
            ctx.restore()
        }
        ctx.restore()
    }
}