Method drawCircle

src/openlayers/overlay/HeatMap.js:277–293

* @function HeatMap.drawCircle * @description 绘制热点半径圆。 * @param {number} r - 热点半径。 * @private

(r)

     * @private
     */
    drawCircle(r) {
        var blur = r / 2;

        var circle = this.circle = document.createElement('canvas'),
            ctx = circle.getContext("2d");

        circle.height = 2 * r;
        circle.width = 2 * r;
        ctx.shadowOffsetX = ctx.shadowOffsetY = 2 * r;
        ctx.shadowBlur = blur;
        ctx.shadowColor = "#000000";

        ctx.beginPath();
        ctx.arc(-r, -r, r / 2, 0, Math.PI * 2, true);
        ctx.closePath();
        ctx.fill();
    }

    /**
     * @function HeatMap.createGradient