var ctx = wx.createCanvasContext('base');
    var centerX = 375/ 2;
    var centerY = 200;
    var rotate = 90;
    var scale = 2;
    ctx.save();//保存状态
    ctx.translate(centerX, centerY)
    ctx.rotate(rotate * Math.PI / 180);
    ctx.scale(scale, scale);

    ctx.setFillStyle("#FF0000");
    ctx.setFontSize(20);
    ctx.setTextAlign('center');
    ctx.setTextBaseline('middle');
    ctx.fillText('Hello World', 0, 0);
    ctx.restore();//恢复状态
    ctx.draw();