MapBox GL集成自定义Canvas制作动态效果

问题描述

当我们在使用MapBox过程中，有时需要添加动态图标或者一些其他复杂的效果。由于MapBox未提供添加GIF格式图片的接口。所以添加起来比较麻烦。而往往这些效果使用HTML或使用Canvas绘制很容易实现，所以本文主要介绍如何在MapBox中集成HTML或集成自定义Canvas效果。

相关接口

MapBox提供了addImage(id,image,options)方法，其具体介绍如下：

 Add an image to the style. This image can be displayed on the map like any other icon in the style's sprite using the image's ID with icon-image, background-pattern, fill-pattern, or line-pattern. A Map#error event will be fired if there is not enough space in the sprite to add this image.

Parameters
id(string)The ID of the image.
image((HTMLImageElement | ImageBitmap | ImageData | {width: number, height: number, data: (Uint8Array | Uint8ClampedArray)} | StyleImageInterface))The image as an HTMLImageElement , ImageData , ImageBitmap or object with width , height , and data properties with the same format as ImageData .

从接口中，我们可以看到，在image参数中，可以使用HTMLImageElement图片，我们可以查看HTMLImageElement的介绍。这就为我们使用自动有HTML或Canvas提供了方法。

官方示例

在MapBox的官方示例中提供了一种绘制动态点的例子。Add an animated icon to the map。该示例如下：

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Add an animated icon to the map</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://api.mapbox.com/mapbox-gl-js/v1.8.1/mapbox-gl.js"></script>
<link href="https://api.mapbox.com/mapbox-gl-js/v1.8.1/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 = '<your access token here>';
var map = new mapboxgl.Map({
container: 'map',
style: 'mapbox://styles/mapbox/streets-v9'
});
 
var size = 200;
 
// implementation of CustomLayerInterface to draw a pulsing dot icon on the map
// see https://docs.mapbox.com/mapbox-gl-js/api/#customlayerinterface for more info
var pulsingDot = {
width: size,
height: size,
data: new Uint8Array(size * size * 4),
 
// get rendering context for the map canvas when layer is added to the map
onAdd: function() {
var canvas = document.createElement('canvas');
canvas.width = this.width;
canvas.height = this.height;
this.context = canvas.getContext('2d');
},
 
// called once before every frame where the icon will be used
render: function() {
var duration = 1000;
var t = (performance.now() % duration) / duration;
 
var radius = (size / 2) * 0.3;
var outerRadius = (size / 2) * 0.7 * t + radius;
var context = this.context;
 
// draw outer circle
context.clearRect(0, 0, this.width, this.height);
context.beginPath();
context.arc(
this.width / 2,
this.height / 2,
outerRadius,
0,
Math.PI * 2
);
context.fillStyle = 'rgba(255, 200, 200,' + (1 - t) + ')';
context.fill();
 
// draw inner circle
context.beginPath();
context.arc(
this.width / 2,
this.height / 2,
radius,
0,
Math.PI * 2
);
context.fillStyle = 'rgba(255, 100, 100, 1)';
context.strokeStyle = 'white';
context.lineWidth = 2 + 4 * (1 - t);
context.fill();
context.stroke();
 
// update this image's data with data from the canvas
this.data = context.getImageData(
0,
0,
this.width,
this.height
).data;
 
// continuously repaint the map, resulting in the smooth animation of the dot
map.triggerRepaint();
 
// return `true` to let the map know that the image was updated
return true;
}
};
 
map.on('load', function() {
map.addImage('pulsing-dot', pulsingDot, { pixelRatio: 2 });
 
map.addSource('points', {
'type': 'geojson',
'data': {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [0, 0]
}
}
]
}
});
map.addLayer({
'id': 'points',
'type': 'symbol',
'source': 'points',
'layout': {
'icon-image': 'pulsing-dot'
}
});
});
</script>
 
</body>
</html>

修改示例

在我们自定义HTML或Canvas时，只需更改上述示例中的pulsingDot即可。下面我们修改一个扇形扫描的效果。

var pulsingDot= {
      width: size,
      height: size,
      data: new Uint8Array(size * size * 4),
      // get rendering context for the map canvas when layer is added to the map
      onAdd: function () {
        let canvas = document.createElement('canvas');
        canvas.width = this.width;
        canvas.height = this.height;
        this.context = canvas.getContext('2d');
      },

      // called once before every frame where the icon will be used
      render: function () {
        let t = (performance.now() % duration) / duration;

        let radius = (size / 2) * 0.3;
        let outerRadius = (size / 2) * 0.7 * t + radius;
        let context = this.context;
        context.clearRect(0, 0, this.width, this.height);
        context.beginPath();
        context.arc(
          this.width / 2,
          this.height / 2,
          outerRadius,
          0,
          Math.PI * 2
        );
        context.fillStyle = 'rgba(' + colorList[0] + ',' + colorList[1] + ',' + colorList[2] + ',' + (1 - t) + ' )';
        context.fill();

        // draw inner circle
        context.beginPath();
        context.arc(
          this.width / 2,
          this.height / 2,
          radius,
          0,
          Math.PI * 2
        );
        this.data = context.getImageData(
          0,
          0,
          this.width,
          this.height
        ).data;

        // continuously repaint the map, resulting in the smooth animation of the dot
        map.triggerRepaint();

        // return `true` to let the map know that the image was updated
        return true;
      }
    };

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