DeltaFrame

DeltaFrame is a lightweight animation and game loop manager.

Note: Extra features like tasks will now go into deltaframe-extra. This package, deltaframe, will remain a small and fast game loop manager while extra features like tasks will go into deltaframe-extra for those who want the extra features.

Installation

To install this module through npm, simply use the following command:

$ npm install deltaframe

and to use it, you can import it as an ES6 module:

// Webpack
import Deltaframe from 'deltaframe';
 
// Browser
import Deltaframe from './node_modules/deltaframe/deltaframe.js';

Initialization

After installing Deltaframe, it can be initialized like so:

const deltaframe = new Deltaframe();

Deltaframe also accepts an options object at initialization with the following options available:

So an example of initializating Deltaframe with options is:

const options = {
  minFps: 40,
  maxRestartAttempts: 10
};
 
const deltaframe = new Deltaframe(options);

From here you can use any of the conversion features available.

API

Deltaframe all revolves around a function you pass to it and this function should contain your drawing code.

For example, we'll take a simple game loop that moves a circle.

Traditionally, with requestAnimationFrame it would be accomplished like so:

const canvas = document.getElementById('myCanvas');
const ctx = canvas.getContext('2d');
 
let x = canvas.width / 2;
let y = canvas.height - 30;
 
function drawCircle() {
  ctx.beginPath();
  ctx.arc(x, y - 30, 10, 0, Math.PI * 2);
  ctx.fillStyle = '#0095DD';
  ctx.fill();
  ctx.closePath();
}
 
function draw(time) {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  
  drawCircle();
 
  x += 2;
  y += -2;
 
  requestAnimationFrame(draw);
}
 
requestAnimationFrame(draw);

This example uses drawCircle to just draw a circle centered horizontally and near the bottom of the canvas and then it uses requestAnimationFrame recursively to keep the loop going and it makes the ball go diagonally.

To change this so that it uses deltaframe instead, use the following:

const canvas = document.getElementById('myCanvas');
const ctx = canvas.getContext('2d');
 
let x = canvas.width / 2;
let y = canvas.height - 30;
 
function drawCircle() {
  ctx.beginPath();
  ctx.arc(x, y - 30, 10, 0, Math.PI * 2);
  ctx.fillStyle = '#0095DD';
  ctx.fill();
  ctx.closePath();
}
 
function draw(time, delta, deltaAverage) {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  
  drawCircle();
 
  x += 2;
  y += -2;
}
 
deltaframe.start(draw);

The biggest difference here is removing all calls to requestAnimationFrame and just using deltaframe.start(draw) instead. You'll also notice now that the draw function now accepts two more parameters because deltaframe returns three values which can be used inside of your drawing function. The time parameter is the same as it is in the first example, its the DOMHighResTimestamp as returned from requestAnimationFrame or (window.performance.now() in the case of setTimeout). The delta parameter is the change in time from the last frame to this frame and deltaAverage is the mean of the most recent 10 delta values. These values can all be used inside of the draw function however you deem fit.

start

The start method takes a function and begins running the deltaframe loop on it.

const canvas = document.getElementById('myCanvas');
const ctx = canvas.getContext('2d');
 
let x = canvas.width / 2;
let y = canvas.height - 30;
 
function drawCircle() {
  ctx.beginPath();
  ctx.arc(x, y - 30, 10, 0, Math.PI * 2);
  ctx.fillStyle = '#0095DD';
  ctx.fill();
  ctx.closePath();
}
 
function draw(time, delta, deltaAverage) {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  
  drawCircle();
 
  x += 2;
  y += -2;
}
 
deltaframe.start(draw);

pause

The pause method temprarily stops the deltaframe loop. This should only be used if you plan on resuming it at some point and not just stopping entirely.

Note that deltaframe automatically pauses when the user switches tabs.

// Start the drawing loop.
deltaframe.start(draw);
 
setTimeout(() => {
  // After one second the drawing loop will pause and the game will look 'frozen'.
  deltaframe.pause();
}, 1000);

resume

The resume method resumes the deltaframe loop after a paused state. Everything will be where it was before it was paused so it will seem like it was never even paused.

Note that deltaframe automatically resumes from being paused when the user switches back to the tab containing deltaframe.

// Start the drawing loop.
deltaframe.start(draw);
 
setTimeout(() => {
  // After one second the drawing loop will pause and the game will look 'frozen'.
  deltaframe.pause();
 
  setTimeout(() => {
    // After two seconds resume the drawing loop like it was never even paused.
    deltaframe.resume();
  }, 2000);
}, 1000);

stop

The stop method stops the game and resets all deltaframe values back to their original values.

Note that this should only be used when you are done with the animation or drawing. In order to start the loop again you have to call start and provide the drawing function.

// Start the drawing loop.
deltaframe.start(draw);
 
// If some imaginary condition is met, stop deltaframe from running any more.
if (someConditionThatEndsTheAnimation) {
  deltaframe.stop();
}

Tests

The tests for Deltaframe are browser based so to run them you will first need to start the local testing server like so:

$ npm run test

then you will need to navigate to https://localhost/test/index.html in your browser to run all of the available tests for Deltaframe.

License

MIT