巧用Openlayers4的Style

原文：https://blog.csdn.net/gisshixisheng/article/details/80149087

概述

非常细化Openlayers4中的StyleFunction，因为它可以让我非常方便的实现各种效果，本文带你一起一探究竟。
StyleFunction

StyleFunction是一个样式函数，参数包括：feature和resolution，如下图。

不过，一般来说，resolution我用的很少，我一般会用zoom替换掉resolution这个参数；StyleFunction的返回值包括两种：样式或样式数组，如上图API。

样例

随着缩放点大小变化

function styleFunction(feature) {
        var _zoom = map.getView().getZoom(),
            _radius = _zoom*2;

        _radius = _radius<2?2:_radius;
        _radius = _radius>15?15:_radius;

        return new ol.style.Style({
            image: new ol.style.Circle({
                radius: _radius,
                fill: new ol.style.Fill({
                    color: '#ff0000'
                }),
                stroke: new ol.style.Stroke({
                    color: '#ff0000',
                    width: 2
                })
            })
        })
    }

2、级别>4的时候出现标注

 function styleFunction(feature) {
        var _zoom = map.getView().getZoom(),
            _radius = _zoom*2;

        _radius = _radius<2?2:_radius;
        _radius = _radius>15?15:_radius;

        var _attr = feature.get("attribute");
        var _count = _zoom<5?"":_attr.count;

        return new ol.style.Style({
            image: new ol.style.Circle({
                radius: _radius,
                fill: new ol.style.Fill({
                    color: '#ff0000'
                }),
                stroke: new ol.style.Stroke({
                    color: '#ff0000',
                    width: 2
                })
            }),
            text: new ol.style.Text({
                text: _count.toString(),
                font:"bold 12px Times New Roman",
                fill: new ol.style.Fill({
                    color: '#fff'
                })
            })
        })
    }

3、样式组合
样式组合

 function styleFunction(feature) {
        var styles = [];

        styles.push(
            new ol.style.Style({
                image: new ol.style.Circle({
                    radius: 10,
                    fill: new ol.style.Fill({
                        color: '#ff0000'
                    }),
                    stroke: new ol.style.Stroke({
                        color: '#ff0000',
                        width: 2
                    })
                })
            })
        );

        styles.push(
            new ol.style.Style({
                geometry: feature.getGeometry(),
                image: new ol.style.RegularShape({
                    radius1: 10,
                    radius2: 5,
                    points: 8,
                    fill: new ol.style.Fill({
                        color: '#fff'
                    })
                })
            })
        );

        return styles;
    }

4、展示线的节点
展示节点

  function styleFunction(feature) {
        var styles = [];

        styles.push(
            new ol.style.Style({
                stroke: new ol.style.Stroke({
                    color: '#ff0000',
                    width: 4
                })
            })
        );

        var _coords = feature.get("geometry").getCoordinates();
        for(var i=0;i<_coords.length;i++){
            styles.push(
                new ol.style.Style({
                    geometry: new ol.geom.Point(_coords[i]),
                    image: new ol.style.Circle({
                        radius: 4,
                        fill: new ol.style.Fill({
                            color: '#ffff'
                        }),
                        stroke: new ol.style.Stroke({
                            color: '#ff0000',
                            width: 2
                        })
                    })
                })
            );
        }

        return styles;
    }

5、带箭头的线
带箭头的线

 function styleFunction(feature) {
        var styles = [];

        styles.push(
            new ol.style.Style({
                stroke: new ol.style.Stroke({
                    color: '#ff0000',
                    width: 4
                })
            })
        );

        var geometry = feature.get("geometry");
        geometry.forEachSegment(function(start, end) {
            var dx = end[0] - start[0];
            var dy = end[1] - start[1];
            var rotation = Math.atan2(dy, dx);
            // arrows
            styles.push(new ol.style.Style({
                geometry: new ol.geom.Point(end),
                image: new ol.style.Icon({
                    src: '../data/arrow.png',
                    anchor: [0.75, 0.5],
                    rotateWithView: false,
                    rotation: -rotation
                })
            }));
        });

        return styles;
    }