simple-gameloop
v2.1.0
Published
A simple canvas gameloop with a fixed update rate and dynamic render rate
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Simple Gameloop
A small library for running a simulation with a fixed update rate and a variable render rate.
The update
function will be run at the set rate (times per second).
The render
function is tied to requestAnimationFrame
and so runs when the browser says it can.
The update
function is called inside the requestAnimationFrame
call, but only when enough time has passed (tracked via an accumulator) since the last time update
was called. This ensures that the update
function is called at a set rate, regardless of how frequently requestAnimationFrame
runs.
See changelog.md
for changes.
To Use
import * as simpleGameloop from 'simple-gameloop';
/**
* @param dt - time in seconds since last call to update function
*/
const update = function update(dt) {
// your update logic here
};
const render = function render() {
// your render logic here
};
simpleGameloop.createLoop({
update,
render,
});
Create Canvas
There is also a helper function for creating a canvas element of a given size that returns useful references.
const canvasObj = simpleGameloop.createCanvas({
containerSelector: '.canvasContainer',
classes: 'canvas other-class',
width: 500,
height: 500,
});
This will create a 500x500 canvas inside the .canvasContainer
element with the classes canvas
and other-class
.
canvasObj
contains references to:
element
the result of thedocument.createElement('canvas')
call.context
the canvas context (e.g.element.getContext('2d')
).canvas
a reference tocontext.canvas
.
Loop Example
These files are included in the example
directory in the repo.
Run them with npm run example
.
index.html
<!doctype html>
<html>
<head>
<title>Simple Gameloop Example</title>
</head>
<body>
<canvas></canvas>
<script src="index.ts"></script>
</body>
</html>
index.ts
import * as simpleGameloop from '../dist';
const ctx = document.querySelector('canvas')?.getContext('2d');
if (!ctx) {
throw new Error('Canvas Missing');
}
ctx.canvas.style.cssText = 'border: 1px solid black';
const square = {
x: 10,
y: 40,
width: 30,
height: 20,
};
/**
* Update the state of the scene.
*
* @param dt - time in seconds since last call to update function
*/
const update = function update(dt: number) {
// Move square right at 50 pixels per second.
square.x += 50 * dt;
// Wrap the square back to the left edge if it goes off the right edge.
square.x -= square.x > ctx.canvas.width ? ctx.canvas.width : 0;
};
/**
* Draw the scene.
*/
const render = function render() {
// Reset the canvas.
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
// Draw square.
ctx.fillRect(square.x, square.y, square.width, square.height);
// Draw square again if it is transitioning from right edge to left edge.
if (square.x + square.width > ctx.canvas.width) {
ctx.fillRect(square.x - ctx.canvas.width, square.y, square.width, square.height);
}
};
simpleGameloop.createLoop({
update,
render,
// Optionally pass in the canvas context and `fps: true` to render the FPS on the canvas.
ctx,
fps: true,
});
To Do
createLoop
should return an object with the following methods:
pause
to stop calling the update function.play
to start calling the update function.setUpdateRate
if you want to set how many times the update function is called per second. Default is 60.setSpeed
allows you to set the speed of the simulation. Set below 1 for slow motion. Default is 1.