Question

当我用＆line-dasharray＆＃39;绘制虚线时属性，它表现得很奇怪 - 缩放时线条和间隙的长度会发生变化。查看示例。问题：如何绘制具有恒定线和间隙长度的虚线，当我放大/缩小时它不会改变？

//这个愚蠢的机器人说我的帖子主要是代码。不知道其中有什么错误，

//但必须添加一些愚蠢的文字行

＆＃13;

    <!DOCTYPE html>
    <html>
    <head>
    <meta charset='utf-8' />
    <title>Add a GeoJSON line</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
    </head>
    <body>

    <div id='map'></div>
    <script>
    mapboxgl.accessToken = 'pk.eyJ1IjoibHVjYXN3b2oiLCJhIjoiY2l5Nmg4cWU1MDA0ejMzcDJtNHJmZzJkcyJ9.WhcEdTYQH6sSw2pm0RSP9Q';
    var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/streets-v9',
    center: [-122.486052, 37.830348],
    zoom: 15
    });

    map.on('load', function () {

    map.addLayer({
        "id": "route",
        "type": "line",
        "source": {
            "type": "geojson",
            "data": {
                "type": "Feature",
                "properties": {},
                "geometry": {
                    "type": "LineString",
                    "coordinates": [
                        [-122.48369693756104, 37.83381888486939],
                        [-122.48348236083984, 37.83317489144141],
                        [-122.48339653015138, 37.83270036637107],
                        [-122.48356819152832, 37.832056363179625],
                        [-122.48404026031496, 37.83114119107971],
                        [-122.48404026031496, 37.83049717427869],
                        [-122.48348236083984, 37.829920943955045],
                        [-122.48356819152832, 37.82954808664175],
                        [-122.48507022857666, 37.82944639795659],
                        [-122.48610019683838, 37.82880236636284],
                        [-122.48695850372314, 37.82931081282506],
                        [-122.48700141906738, 37.83080223556934],
                        [-122.48751640319824, 37.83168351665737],
                        [-122.48803138732912, 37.832158048267786],
                        [-122.48888969421387, 37.83297152392784],
                        [-122.48987674713133, 37.83263257682617],
                        [-122.49043464660643, 37.832937629287755],
                        [-122.49125003814696, 37.832429207817725],
                        [-122.49163627624512, 37.832564787218985],
                        [-122.49223709106445, 37.83337825839438],
                        [-122.49378204345702, 37.83368330777276]
                    ]
                }
            }
        },
        "paint": {
            "line-color": "#888",
            "line-width": 8,
            "line-dasharray": [5, 5]
        }
    });
});
</script>

</body>
</html>

＆＃13;

Answer 1

好吧，我找到了一些让它变得更好的东西，但它仍然不完美，因为虚线随着缩放而不断变化。

答案的一部分是线条之间的间隙以线宽单位指定，而不是像素。当线宽恒定（以像素为单位）并且不依赖于缩放时，当缩放级别改变时，它的大小（例如，以米为单位）会变大或变小。这导致线之间的间隙也发生变化。 Here您可以找到如何使用可变宽度制作线条的说明，这取决于缩放级别并保留其相对大小。

以下是我将此方法应用于我的示例（它变得更好，但在放大/缩小时仍然会更改行）：

<!DOCTYPE html>
    <html>
    <head>
    <meta charset='utf-8' />
    <title>Add a GeoJSON line</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
    </head>
    <body>

    <div id='map'></div>
    <script>

    
    mapboxgl.accessToken = 'pk.eyJ1IjoibHVjYXN3b2oiLCJhIjoiY2l5Nmg4cWU1MDA0ejMzcDJtNHJmZzJkcyJ9.WhcEdTYQH6sSw2pm0RSP9Q';
    var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/streets-v9',
    center: [-122.486052, 37.830348],
    zoom: 15
    });

    map.on('load', function () {
    let baseWidth = 5;
    let baseZoom = 15;

    map.addLayer({
        "id": "route",
        "type": "line",
        "source": {
            "type": "geojson",
            "data": {
                "type": "Feature",
                "properties": {},
                "geometry": {
                    "type": "LineString",
                    "coordinates": [
                        [-122.48369693756104, 37.83381888486939],
                        [-122.48348236083984, 37.83317489144141],
                        [-122.48339653015138, 37.83270036637107],
                        [-122.48356819152832, 37.832056363179625],
                        [-122.48404026031496, 37.83114119107971],
                        [-122.48404026031496, 37.83049717427869],
                        [-122.48348236083984, 37.829920943955045],
                        [-122.48356819152832, 37.82954808664175],
                        [-122.48507022857666, 37.82944639795659],
                        [-122.48610019683838, 37.82880236636284],
                        [-122.48695850372314, 37.82931081282506],
                        [-122.48700141906738, 37.83080223556934],
                        [-122.48751640319824, 37.83168351665737],
                        [-122.48803138732912, 37.832158048267786],
                        [-122.48888969421387, 37.83297152392784],
                        [-122.48987674713133, 37.83263257682617],
                        [-122.49043464660643, 37.832937629287755],
                        [-122.49125003814696, 37.832429207817725],
                        [-122.49163627624512, 37.832564787218985],
                        [-122.49223709106445, 37.83337825839438],
                        [-122.49378204345702, 37.83368330777276]
                    ]
                }
            }
        },
        "paint": {
            "line-color": "#888",
            "line-width": 
            {
                'type': 'exponential',
                'base': 2,
                'stops': [
                    [0, baseWidth * Math.pow(2, (0 - baseZoom))],
                    [22, baseWidth * Math.pow(2, (22 - baseZoom))]
                ]
            },
            "line-dasharray": [5, 5]
        }
    });
});
</script>

</body>
</html>

Answer 2

通过调整实际的dasharray值，可以得到更好的行为（在我看来）。通过使第一个值小于第二个值（例如[0.2, 2]），缩放变得更有意义。这就是它们在mapbox-gl-draw库中使用的方式。

edit：外观如下：

    <!DOCTYPE html>
    <html>
    <head>
    <meta charset='utf-8' />
    <title>Add a GeoJSON line</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
    </head>
    <body>

    <div id='map'></div>
    <script>
    mapboxgl.accessToken = 'pk.eyJ1IjoibHVjYXN3b2oiLCJhIjoiY2l5Nmg4cWU1MDA0ejMzcDJtNHJmZzJkcyJ9.WhcEdTYQH6sSw2pm0RSP9Q';
    var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/streets-v9',
    center: [-122.486052, 37.830348],
    zoom: 15
    });

    map.on('load', function () {

    map.addLayer({
        "id": "route",
        "type": "line",
        "source": {
            "type": "geojson",
            "data": {
                "type": "Feature",
                "properties": {},
                "geometry": {
                    "type": "LineString",
                    "coordinates": [
                        [-122.48369693756104, 37.83381888486939],
                        [-122.48348236083984, 37.83317489144141],
                        [-122.48339653015138, 37.83270036637107],
                        [-122.48356819152832, 37.832056363179625],
                        [-122.48404026031496, 37.83114119107971],
                        [-122.48404026031496, 37.83049717427869],
                        [-122.48348236083984, 37.829920943955045],
                        [-122.48356819152832, 37.82954808664175],
                        [-122.48507022857666, 37.82944639795659],
                        [-122.48610019683838, 37.82880236636284],
                        [-122.48695850372314, 37.82931081282506],
                        [-122.48700141906738, 37.83080223556934],
                        [-122.48751640319824, 37.83168351665737],
                        [-122.48803138732912, 37.832158048267786],
                        [-122.48888969421387, 37.83297152392784],
                        [-122.48987674713133, 37.83263257682617],
                        [-122.49043464660643, 37.832937629287755],
                        [-122.49125003814696, 37.832429207817725],
                        [-122.49163627624512, 37.832564787218985],
                        [-122.49223709106445, 37.83337825839438],
                        [-122.49378204345702, 37.83368330777276]
                    ]
                }
            }
        },
 layout: {
    'line-join': 'round',
    'line-cap': 'round',
  },
        "paint": {
            "line-color": "#888",
            "line-width": 8,
            "line-dasharray": [0.2, 2]
        }
    });
});
</script>

</body>
</html>

如何绘制在缩放时不会改变的虚线

2 个答案: