Add a custom style layer | TrackAsia GL JS Docs

Use a custom style layer to render custom WebGL content.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Add a custom style layer</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.js"></script>
<link href="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-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>
const map = new trackasiagl.Map({
container: 'map',
zoom: 7,
center: {"lat":10.762622,"lng":106.660172},
style: 'https://maps.track-asia.com/styles/v1/streets.json?key=public_key',
antialias: true // create the gl context with MSAA antialiasing, so custom layers are antialiased
});
 
// create a custom style layer to implement the WebGL content
const highlightLayer = {
id: 'highlight',
type: 'custom',
 
// method called when the layer is added to the map
// https://docs.track-asia.com/api/properties/#styleimageinterface#onadd
onAdd: function (map, gl) {
// create GLSL source for vertex shader
const vertexSource = `#version 300 es
 
uniform mat4 u_matrix;
in vec2 a_pos;
void main() {
gl_Position = u_matrix * vec4(a_pos, 0.0, 1.0);
}`;
 
// create GLSL source for fragment shader
const fragmentSource = `#version 300 es
 
out highp vec4 fragColor;
void main() {
fragColor = vec4(0.9, 0.3, 0.3, 0.9);
}`;
 
// create a vertex shader
const vertexShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertexShader, vertexSource);
gl.compileShader(vertexShader);
 
// create a fragment shader
const fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragmentShader, fragmentSource);
gl.compileShader(fragmentShader);
 
// link the two shaders into a WebGL program
this.program = gl.createProgram();
gl.attachShader(this.program, vertexShader);
gl.attachShader(this.program, fragmentShader);
gl.linkProgram(this.program);
 
this.aPos = gl.getAttribLocation(this.program, 'a_pos');
// define vertices of the triangle to be rendered in the custom style layer
const helsinki = trackasiagl.MercatorCoordinate.fromLngLat({"lng":106.53,"lat":11.244});
const berlin = trackasiagl.MercatorCoordinate.fromLngLat({"lng":106.343,"lat":10.635});
const kyiv = trackasiagl.MercatorCoordinate.fromLngLat({"lng":107.261,"lat":10.78});
 
// create and initialize a WebGLBuffer to store vertex and color data
this.buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, this.buffer);
gl.bufferData(
gl.ARRAY_BUFFER,
new Float32Array([
helsinki.x,
helsinki.y,
berlin.x,
berlin.y,
kyiv.x,
kyiv.y
]),
gl.STATIC_DRAW
);
},
 
// method fired on each animation frame
// https://docs.track-asia.com/api/map/#map.event:render
render: function (gl, matrix) {
gl.useProgram(this.program);
gl.uniformMatrix4fv(
gl.getUniformLocation(this.program, 'u_matrix'),
false,
matrix
);
gl.bindBuffer(gl.ARRAY_BUFFER, this.buffer);
gl.enableVertexAttribArray(this.aPos);
gl.vertexAttribPointer(this.aPos, 2, gl.FLOAT, false, 0, 0);
gl.enable(gl.BLEND);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
gl.drawArrays(gl.TRIANGLE_STRIP, 0, 3);
}
};
 
// add the custom style layer to the map
map.on('load', function () {
map.addLayer(highlightLayer, 'waterway');
});
</script>
 
</body>
</html>