Method getTextWidth

src/common/overlay/levelRenderer/Area.js:1009–1039

* @function LevelRenderer.Tool.Areal.prototype.getTextWidth * @description 测算多行文本宽度

(text, textFont)

     * @description 测算多行文本宽度
     */
    getTextWidth(text, textFont) {
        var key = text + ':' + textFont;
        if (this._textWidthCache[key]) {
            return this._textWidthCache[key];
        }
        this._ctx = this._ctx || this.util.getContext();
        this._ctx.save();

        if (textFont) {
            this._ctx.font = textFont;
        }

        text = (text + '').split('\n');
        var width = 0;
        for (var i = 0, l = text.length; i < l; i++) {
            width = Math.max(
                this._ctx.measureText(text[i]).width,
                width
            );
        }
        this._ctx.restore();

        this._textWidthCache[key] = width;
        if (++this._textWidthCacheCounter > this.TEXT_CACHE_MAX) {
            // 内存释放
            this._textWidthCacheCounter = 0;
            this._textWidthCache = {};
        }

        return width;
    }

    /**
     * @function LevelRenderer.Tool.Areal.prototype.getTextHeight