renderer.CanvasRenderer

renderer.CanvasRenderer is the base renderer that renders a layer on an HTMLCanvasElement, extending LayerAbstractRenderer. It creates the canvas 2D context, resets/clears/clips the canvas during the render lifecycle, and fires layer events such as canvascreate, renderstart, renderend, and resourceload. It is normally created internally by renderers and usually not instantiated directly.

import { renderer } from "maptalks";

// Usually created internally by the layer
const r = new renderer.CanvasRenderer(layer);

Constructor

new CanvasRenderer(layer)

Parameters:

• layer Layer — The layer to be rendered.

Options

CanvasRenderer has no standalone options; rendering-related configuration is controlled by the options of the layer being rendered, such as forceRenderOnMoving (whether to force a redraw while moving), globalCompositeOperation (canvas composite mode), and renderer (renderer type). See the options docs of each layer.

Methods

• needToRedraw(): boolean — Whether the current frame needs a redraw; returns true while the map is interacting or the view has changed.
• createContext(): void — Create the 2D context for the current canvas and apply the device pixel ratio and composite mode.
• resetCanvasTransform(): void — Reset the canvas transform according to the device pixel ratio.
• clearCanvas(): void — Clear the canvas to blank.
• clear(): void — Clear the canvas and mark it for redraw.
• prepareCanvas(): PointExtent — Prepare the canvas for rendering: create the canvas on first use or reset/clear the existing one, and return the mask's 2D extent.
• onResize(param): void — On map resize, drop the extent cache, resize the canvas, and redraw.

Events

The renderer fires the following layer events via layer.fire:

• canvascreate — Fired when the canvas is created; the event payload includes context and gl.
• renderstart — Fired when the layer starts rendering; the event payload includes context and gl.
• renderend — Fired when the layer finishes rendering.
• resourceload — Fired when the layer finishes loading resources.