QT Transform / Scale bigger than 1 gets slow

import QtQuick 2.0

Rectangle {
    width: 480
    height: 480

    Canvas {
        id: canvas
        anchors.fill: parent
        property double scale: 1
        property var ctx;
        onAvailableChanged: {
            if(available) {
                console.log("canvas available")
                ctx = canvas.getContext('2d');
                console.log(ctx)
            }
        }
        MouseArea {
           id: mousearea
           property int hitrad: 5;
           anchors.fill: parent
           onWheel: {
               if(wheel.angleDelta.y > 0) {
                   canvas.scale += canvas.scale * 0.2;
               } else {
                   canvas.scale -= canvas.scale * 0.2;
               }
               canvas.ctx.clearRect(0, 0, width, height);
               canvas.requestPaint();
           }
        }
        onPaint: {
            ctx.reset();
            var distance = ctx.lineWidth * 4;
            ctx.scale(scale,scale);

            // Using connected paths is slow:
            ctx.beginPath();
            ctx.moveTo(0, i * distance);
            for (var i = 0; i < 200; ++i) {
                ctx.lineTo(300 + Math.random() * 100, i * distance + 100);
                ctx.lineTo(0 + Math.random() * 100, i * distance);
            }
            ctx.stroke();

            // While creating individual paths isn't:
//            for (var i = 0; i < 200; ++i) {
//                ctx.beginPath();
//                ctx.moveTo(300 + Math.random() * 100, i * distance + 100);
//                ctx.lineTo(0 + Math.random() * 100, i * distance);
//                ctx.stroke();
//            }
        }
    }
}