Skip To ContentArcGIS for DevelopersSign In Dashboard
require(["esri/views/2d/layers/BaseLayerViewGL2D"], function(BaseLayerViewGL2D) { /* code goes here */ });
Class: esri/views/2d/layers/BaseLayerViewGL2D
Inheritance: BaseLayerViewGL2D LayerView Accessor
Since: ArcGIS API for JavaScript 4.11
beta

Represents the LayerView of a Layer after it has been added to a Map with a MapView. In contrast to the related class BaseLayerView2D, this one exposes WebGL rendering capabilities.

Important notes

This interface is experimental. Please read the following information carefully before using it in a product.

Due to the nature of WebGL it is not possible to fully sandbox user-supplied code, and its malfunctions can affect the performance, visual quality and even stability of the entire MapView. For this reason, Esri does not provide any support for issues related to WebGL rendering in custom rendering code, or for issues that arise in MapView rendering while using custom rendering code.

This class may be extended to create a custom LayerView for a Layer. A LayerView is created on demand by the MapView when a layer is added the to list of layers of its map.

The subclass can implement multiple functions of the LayerView lifecycle.

  • First, the attach() method is called when the LayerView is about to start drawing the layer's content; it is usually responsible for resource allocation.
  • Then during the life of the LayerView the render() method is called once per frame; it must complete drawing before returning.
  • Finally the detach() method is called after the layer is removed from the map; it releases all allocated resources and stops on-going requests.

Each of these functions has access to the MapView's WebGL context through the instance property this.context.

Example:
var CustomLayerView2D = BaseLayerViewGL2D.createSubclass({
   render(renderParameters) {
     const gl = this.context;

     ...
   }

   attach() {
     const gl = this.context;

     ...
   }

   detach() {
     const gl = this.context;

     ...
   }
 });

 var CustomTileLayer = Layer.createSubclass({
   tileInfo: TileInfo.create({ spatialReference: { wkid: 3857 }}),

   createLayerView(view) {
     if (view.type === "2d") {
       return new CustomLayerView2D({
         view: view,
         layer: this
       });
     }
   }
 });

Constructors

new BaseLayerViewGL2D(properties)
Parameter:
properties Object
optional

See the properties for a list of all the properties that may be passed into the constructor.

Property Overview

Any properties can be set, retrieved or listened to. See the Working with Properties topic.
NameTypeSummaryClass
WebGLRenderingContext|WebGL2RenderingContext

The WebGL rendering context associated to this layer view.

more details
more detailsBaseLayerViewGL2D
String

The name of the class.

more details
more detailsAccessor
Layer

References the layer this LayerView represents.

more details
more detailsBaseLayerViewGL2D
Boolean

Value is true if the layer is suspended (i.e., layer will not redraw or update itself when the extent changes).

more details
more detailsLayerView
Tile[]

The array of Tile objects computed to cover the MapView's visible area.

more details
more detailsBaseLayerViewGL2D
Boolean

Value is true when the layer is updating; for example, if it is in the process of fetching data.

more details
more detailsLayerView
MapView

References the MapView this LayerView belongs to.

more details
more detailsBaseLayerViewGL2D
Boolean

When true, the layer is visible in the view.

more details
more detailsLayerView

Property Details

context WebGLRenderingContext|WebGL2RenderingContext

The WebGL rendering context associated to this layer view.

declaredClass Stringreadonly inherited

The name of the class. The declared class name is formatted as esri.folder.className.

layer Layer

References the layer this LayerView represents.

suspended Booleanreadonly inherited

Value is true if the layer is suspended (i.e., layer will not redraw or update itself when the extent changes).

tiles Tile[]

The array of Tile objects computed to cover the MapView's visible area. This array is updated when the view is animating or the user is interacting with it. Then if tiles have been added or removed, tilesChanged() is called.

See also:
updating Booleanreadonly inherited

Value is true when the layer is updating; for example, if it is in the process of fetching data.

Default Value:false
view MapView

References the MapView this LayerView belongs to.

When true, the layer is visible in the view. Set this property to false to hide the layer from the view.

Default Value:true

Method Overview

NameReturn TypeSummaryClass

Method called after the LayerView is created and right before it starts drawing the layer's content.

more details
more detailsBaseLayerViewGL2D

Method called after the layer is removed and the LayerView is about to be removed.

more details
more detailsBaseLayerViewGL2D
Promise<Graphic>

Method to implement that is responsible for providing objects hit at the specified screen coordinates.

more details
more detailsBaseLayerViewGL2D
Boolean

isFulfilled() may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected).

more details
more detailsLayerView
Boolean

isRejected() may be used to verify if creating an instance of the class is rejected.

more details
more detailsLayerView
Boolean

isResolved() may be used to verify if creating an instance of the class is resolved.

more details
more detailsLayerView

The method to implement that is responsible of drawing the content of the layer.

more details
more detailsBaseLayerViewGL2D

The LayerView can call this method to ask the MapView to schedule a new rendering frame.

more details
more detailsBaseLayerViewGL2D

Method to implement, which notifies of tiles being added or removed for the current view state.

more details
more detailsBaseLayerViewGL2D
Promise

when() may be leveraged once an instance of the class is created.

more details
more detailsLayerView

Method Details

attach()

Method called after the LayerView is created and right before it starts drawing the layer's content. Typically this method is implemented to start watching property changes on the layer and to initialize WebGL objects such as shaders.

See also:
Example:
// Create a shader program and a property watcher
attach() {
  var gl = this.context;

  this._shaderProgram = gl.createProgram();
  ...

  this._propertyHandle = this.layer.watch("opacity", function() {
    this.requestRender();
  });
}
detach()

Method called after the layer is removed and the LayerView is about to be removed. Typically, this method is implemented to free resources like watchers and destroy WebGL objects such as shader programs.

See also:
Example:
// Remove the watchers and destroy the shader program created in attach()
detach() {
  this._propertyHandle.remove();
  this._propertyHandle = null;

  const gl = this.context;

  gl.deleteProgram(this._shaderProgram);
  this._shaderProgram = null;
}
hitTest(x, y){Promise<Graphic>}

Method to implement that is responsible for providing objects hit at the specified screen coordinates. This method is called internally by the MapView each time its hitTest() method is called.

Parameters:

The x-coordinate in screen space of the desired hit.

The y-coordinate in screen space of the desired hit.

Returns:
TypeDescription
Promise<Graphic>A Promise that can resolve with a hit graphic instance.
isFulfilled(){Boolean}inherited

isFulfilled() may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected). If it is fulfilled, true will be returned.

Returns:
TypeDescription
BooleanIndicates whether creating an instance of the class has been fulfilled (either resolved or rejected).
isRejected(){Boolean}inherited

isRejected() may be used to verify if creating an instance of the class is rejected. If it is rejected, true will be returned.

Returns:
TypeDescription
BooleanIndicates whether creating an instance of the class has been rejected.
isResolved(){Boolean}inherited

isResolved() may be used to verify if creating an instance of the class is resolved. If it is resolved, true will be returned.

Returns:
TypeDescription
BooleanIndicates whether creating an instance of the class has been resolved.
render(renderParameters)

The method to implement that is responsible of drawing the content of the layer. This method is called every time the MapView's state changes, or if requestRender() has been called.

Parameters:
Specification:
renderParameters Object
Specification:
context WebGLRenderingContext|WebGL2RenderingContext

The WebGL or WebGL 2 context. Its concrete type depends on system configuration. Every time that render() is called, the API automatically resets WebGL to a conventional state which is almost the default one; the only two things that may be non-default are the bound framebuffer and the viewport, which is set to match the entire framebuffer. The body of render() must not change these settings.

stationary Boolean

The stationary state of the MapView.

state ViewState

The object that describes view state.

Example:
// Example of a render implementation that draws using a custom shader program
render(renderParameters) {
  const gl = this.context;
  gl.bindBuffer(gl.ARRAY_BUFFER, this._vertexBuffer);
  gl.vertexAttribPointer(0, 2, gl.SHORT, false, 10, 0);
  gl.vertexAttribPointer(1, 3, gl.SHORT, true, 10, 4);
  gl.bindBuffer(gl.ARRAY_BUFFER, null);
  gl.enableVertexAttribArray(0);
  gl.enableVertexAttribArray(1);
  ...
  // Update uniforms as needed by calling gl.uniform...
  ...
  gl.useProgram(this._shaderProgram);
  gl.drawArrays(gl.TRIANGLES, 0, this._vertexCount);
  gl.disableVertexAttribArray(0);
  gl.disableVertexAttribArray(1);
  gl.useProgram(null);
}
requestRender()

The LayerView can call this method to ask the MapView to schedule a new rendering frame.

Example:
// Call requestRender whenever the layer opacity has changed
attach() {
  this._propertyHandle = this.layer.watch("opacity", function() {
    this.requestRender();
  });
}
tilesChanged(added, removed)

Method to implement, which notifies of tiles being added or removed for the current view state. This function can be implemented to start and stop fetching new data, or allocate and dispose resources.

Parameters:
added Tile[]

The tile objects added for the current view viewport.

removed Tile[]

The tile objects removed from the view viewport.

when(callback, errback){Promise}inherited

when() may be leveraged once an instance of the class is created. This method takes two input parameters: a callback function and an errback function. The callback executes when the instance of the class loads. The errback executes if the instance of the class fails to load.

Parameters:
callback Function
optional

The function to call when the promise resolves.

errback Function
optional

The function to execute when the promise fails.

Returns:
TypeDescription
PromiseReturns a new promise for the result of callback that may be used to chain additional functions.
Example:
// Although this example uses MapView, any class instance that is a promise may use then() in the same way
var view = new MapView();
view.when(function(){
  // This function will execute once the promise is resolved
}, function(error){
  // This function will execute if the promise is rejected due to an error
});

Type Definitions

Tile Object

Represents a tile reference.

Properties:

The tile string identifier in the format level/row/col/world

level Number

The level identifier of the LOD to which the tile belongs

row Number

The row identifier.

col Number

The column identifier.

world Number

When the projection allows world wrapping (e.g. Web Mercator), identifies the instance of the world this tile's level/row/col.

resolution Number

The number of map units per pixel in the tile.

scale Number

The map scale at the tile's level.

coords Number[]

The coordinates of the top-left corner of the tile as an array of two numbers. The coordinates are in un-normalized map units.

bounds Number[]

The bounds of the tile as an array of four numbers that be readily converted to an Extent object.

API Reference search results

NameTypeModule
Loading...