terkelg/deakins

Deakins

Small Canvas 2D Camera

Small and simple 2D viewport/camera management for Canvas. Named after the legendary English cinematographer Roger Deakins known for Blade Runner, Fargo, No Country for Old Men, and The Shawshank Redemption.

Install

$ npm install deakins

This module is delivered as:

• ES Module: dist/index.mjs
• UMD: dist/deakins.umd.js

Usage

import { Deakins } from 'deakins';

const canvas = document.createElement(`canvas`);
const context = canvas.getContext(`2d`);

const camera = new Deakins(context);
const player = new Player();

function loop() {
  camera.begin();

  // Look at point in space,
  camera.lookAt(player.position);

  // Zoom
  camera.zoomTo(500);

  camera.end();
  requestAnimationFrame(loop);
}

loop();

Moving the camera

camera.lookAt([x, y]);

camera.zoomTo(z);

API

Deakins(context, [options])

Initializes a new Deakins camera instance.

context

Type: CanvasRenderingContext2D

options.fieldOfView

Type: number
Default: 1000

This value is used to imitate a FOV camera effect as you zoom.

options.flipAspectRatio

Type: boolean
Default: false

By default, everything scales based on the width of the canvas. When true, the aspect ratio is defined by the height instead.

options.margin

Type: LookAtMargins
Default: {top: 0, right: 0, bottom: 0, left: 0}

Margins for all sides defined in screen space. This is used if the lazy option in lookAt is true. If true, the camera only follows the look-at point when the point is inside the screen space margin.

camera.lookAt(point, [lazy])

Move the centre of the viewport to the location specified by the point.

Call this in the RAF loop to follow a player character, for example.

camera.moveTo([11, 8]);

point

Type: [number, number]
Default: [0, 0]

lazy

Type: boolean
Default: false

Enable lazy look-at. If true, the camera won't move before the look-at point is inside the margin defined in options.margin. If false, the look-at point stays centered. Below is an illustration of a lazy camera.

camera.zoomTo(zoom)

Zoom to the specified distance from the 2D plane.

camera.zoomTo(500);

zoom

Type: number
Default: 1000

camera.begin()

On each render pass, call .begin() before drawing to set the right transforms.

Appropriate transformations will be applied to the context, and world coordinates can be used directly with all canvas context calls.

camera.begin();

// Draw stuff here

camera.end();

camera.end()

Call .end() when you're done drawing to reset the context.

camera.worldToScreen(point)

point

Type: [number, number]

Transform a point from world coordinates into screen coordinates - useful for placing DOM elements over the scene.

camera.screenToWorld()

Returns: [number, number]

Transform and return the world space coordinate of the current look-at point.

Useful if you want to project clicks and other screen space coordinates into 2D world coordinates.

camera.resize()

Call this in your resize handler to make sure the viewport is updated.

Credit

TypeScript conversion based on camera by Rob Ashton with minor tweaks. Added support for more options, lazy camera movements, and slightly modified API.

License

MIT © Terkel Gjervig