CustomLayerInterface

Interface for custom style layers. This is a specification for implementers to model: it is not an exported method or class.

Custom layers allow a user to render directly into the map’s GL context using the map’s camera. These layers can be added between any regular layers using Map#addLayer.

Custom layers must have a unique id and must have the type of "custom". They must implement render and may implement prerender, onAdd and onRemove. They can trigger rendering using Map#triggerRepaint and they should appropriately handle MapContextEvent with webglcontextlost and webglcontextrestored.

The renderingMode property controls whether the layer is treated as a "2d" or "3d" map layer. Use:

• "renderingMode": "3d" to use the depth buffer and share it with other layers
• "renderingMode": "2d" to add a layer with no depth. If you need to use the depth buffer for a "2d" layer you must use an offscreen framebuffer and CustomLayerInterface#prerender

Example

Custom layer implemented as ES6 class

class NullIslandLayer {
    constructor() {
        this.id = 'null-island';
        this.type = 'custom';
        this.renderingMode = '2d';
    }

    onAdd(map, gl) {
        const vertexSource = `
        uniform mat4 u_matrix;
        void main() {
            gl_Position = u_matrix * vec4(0.5, 0.5, 0.0, 1.0);
            gl_PointSize = 20.0;
        }`;

        const fragmentSource = `
        void main() {
            fragColor = vec4(1.0, 0.0, 0.0, 1.0);
        }`;

        const vertexShader = gl.createShader(gl.VERTEX_SHADER);
        gl.shaderSource(vertexShader, vertexSource);
        gl.compileShader(vertexShader);
        const fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
        gl.shaderSource(fragmentShader, fragmentSource);
        gl.compileShader(fragmentShader);

        this.program = gl.createProgram();
        gl.attachShader(this.program, vertexShader);
        gl.attachShader(this.program, fragmentShader);
        gl.linkProgram(this.program);
    }

    render(gl, matrix) {
        gl.useProgram(this.program);
        gl.uniformMatrix4fv(gl.getUniformLocation(this.program, "u_matrix"), false, matrix);
        gl.drawArrays(gl.POINTS, 0, 1);
    }
}

map.on('load', () => {
    map.addLayer(new NullIslandLayer());
});

Methods

onAdd()?

optional onAdd(map: Map, gl: WebGLRenderingContext | WebGL2RenderingContext): void

Optional method called when the layer has been added to the Map with Map#addLayer. This gives the layer a chance to initialize gl resources and register event listeners.

Parameters

Returns

void

onRemove()?

optional onRemove(map: Map, gl: WebGLRenderingContext | WebGL2RenderingContext): void

Optional method called when the layer has been removed from the Map with Map#removeLayer. This gives the layer a chance to clean up gl resources and event listeners.

Parameters

Returns

void

Properties

id

id: string

A unique layer id.

prerender?

optional prerender: CustomRenderMethod

Optional method called during a render frame to allow a layer to prepare resources or render into a texture.

The layer cannot make any assumptions about the current GL state and must bind a framebuffer before rendering.

render

render: CustomRenderMethod

Called during a render frame allowing the layer to draw into the GL context.

The layer can assume blending and depth state is set to allow the layer to properly blend and clip other layers. The layer cannot make any other assumptions about the current GL state.

If the layer needs to render to a texture, it should implement the prerender method to do this and only use the render method for drawing directly into the main framebuffer.

The blend function is set to gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA). This expects colors to be provided in premultiplied alpha form where the r, g and b values are already multiplied by the a value. If you are unable to provide colors in premultiplied form you may want to change the blend function to gl.blendFuncSeparate(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA, gl.ONE, gl.ONE_MINUS_SRC_ALPHA).

renderingMode?

optional renderingMode: "2d" | "3d"

Either "2d" or "3d". Defaults to "2d".

type

type: "custom"

The layer’s type. Must be "custom".