Method getLabelInfo

src/mapboxgl/overlay/LabelThemeLayer.js:652–744

* @function LabelThemeLayer.prototype.getLabelInfo * @description 根据当前位置获取绘制后的标签信息，包括标签的宽，高和行数等。 * @returns {Object} 绘制后的标签信息。

(location, style)

     * @returns {Object} 绘制后的标签信息。
     */
    getLabelInfo(location, style) {
        var LABEL_ALIGN = {
                "l": "left",
                "r": "right",
                "t": "top",
                "b": "bottom"
            },
            LABEL_FACTOR = {
                "l": 0,
                "r": -1,
                "t": 0,
                "b": -1
            };

        style = Util.extend({
            fontColor: "#000000",
            labelAlign: "cm"
        }, style);
        var pt = this.getLocalXY(location);
        var labelWidth = 0;

        if (style.labelXOffset || style.labelYOffset) {
            var xOffset = isNaN(style.labelXOffset) ? 0 : style.labelXOffset;
            var yOffset = isNaN(style.labelYOffset) ? 0 : style.labelYOffset;
            pt[0] += xOffset;
            pt[1] -= yOffset;
        }

        var canvas = document.createElement('canvas');
        canvas.globalAlpha = 0;
        canvas.lineWidth = 1;

        var ctx = canvas.getContext("2d");

        ctx.fillStyle = style.fontColor;
        ctx.globalAlpha = style.fontOpacity || 1.0;
        var fontStyle = [style.fontStyle ? style.fontStyle : "normal",
            "normal",
            style.fontWeight ? style.fontWeight : "normal",
            style.fontSize ? style.fontSize : "1em",
            style.fontFamily ? style.fontFamily : "sans-serif"
        ].join(" ");
        var labelRows = style.label.split('\n');
        var numRows = labelRows.length;
        var vfactor, lineHeight, labelWidthTmp;
        if (ctx.fillText) {
            // HTML5
            ctx.font = fontStyle;
            ctx.textAlign = LABEL_ALIGN[style.labelAlign[0]] ||
                "center";
            ctx.textBaseline = LABEL_ALIGN[style.labelAlign[1]] ||
                "middle";
            vfactor = LABEL_FACTOR[style.labelAlign[1]];
            if (vfactor == null) {
                vfactor = -.5;
            }
            lineHeight = ctx.measureText('Mg').height ||
                ctx.measureText('xx').width;