edge background color when erasing

[BPing]

This happened when I cleared the cutting areactx.clip()，you can see that the edges of the clipping area are also cleared into the background color.

[BPing]

   eraser.setErasePathForEraser = function(context) {
        context.beginPath();
        context.arc(eraser.prePiont.loc.x, eraser.prePiont.loc.y,
            eraser.eraserWidth / 2 + ERASER_LINE_WIDTH,
            0, Math.PI * 2, false);
        context.clip();
    };
    eraser.eraseLast = function(context) {
        context.save();
        eraser.setErasePathForEraser(context);
        eraser.crysyanCanvas.clearCanvas();
        context.restore();
    };

        clearCanvas: function () {
            this.playContext.clearRect(0, 0, this.playCanvas.width, this.playCanvas.height);
            this.clearCanvasWithOnlyBackGroupImage();
        },
        //
        clearCanvasWithOnlyBackGroupImage: function () {
            if (this.backgroudImage.image !== null) {
                var image = this.backgroudImage.image;
                this.drawImage(image, (this.playCanvas.width - image.width) / 2, (this.playCanvas.height - image.height) / 2, image.width, image.height);
                return;
            }
        },

In version #crysyan-0.0.9.touch.fix20170309, I solve the problem as follows.But I don't think it's a good idea.

//
    eraser.eraseLast = function (context) {
        // clear
        context.save();
        context.beginPath();
        context.arc(eraser.prePiont.loc.x, eraser.prePiont.loc.y,
            eraser.eraserWidth / 2 + ERASER_LINE_WIDTH,
            0, Math.PI * 2, false);
        context.globalCompositeOperation="destination-out";
        context.fill();
        context.restore();
        // draw backgroup Image
        context.save();
        context.beginPath();
        // Clear edge background color, so the radius of the circle 1 units bigger than the previous
        context.arc(eraser.prePiont.loc.x, eraser.prePiont.loc.y,
            eraser.eraserWidth / 2 + ERASER_LINE_WIDTH+1,
            0, Math.PI * 2, false);
        context.clip();
        eraser.crysyanCanvas.clearCanvasWithOnlyBackGroupImage();
        context.restore();
    };

In latest Version ,there is 3 shapes for eraser,circular\square\path.The above solutions are not suitable for the path shape of the eraser.