Method getTextHeight

src/common/overlay/levelRenderer/Area.js:1045–1072

* @function LevelRenderer.Tool.Areal.prototype.getTextHeight * @description 测算多行文本高度

(text, textFont)

     * @description 测算多行文本高度
     */
    getTextHeight(text, textFont) {
        var key = text + ':' + textFont;
        if (this._textHeightCache[key]) {
            return this._textHeightCache[key];
        }

        this._ctx = this._ctx || this.util.getContext();

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

        text = (text + '').split('\n');
        // 比较粗暴
        //var height = (this._ctx.measureText('国').width + 2) * text.length;  //打包不支持中文，替换掉
        var height = (this._ctx.measureText('ZH').width + 2) * text.length;

        this._ctx.restore();

        this._textHeightCache[key] = height;
        if (++this._textHeightCacheCounter > this.TEXT_CACHE_MAX) {
            // 内存释放
            this._textHeightCacheCounter = 0;
            this._textHeightCache = {};
        }
        return height;
    }
}