I try to make an animation using the following code:
var obst = new Obstacle(x, y)
obst.build()
function animate() {
ctx.clearRect(0, 0, innerWidth, innerHeight);
requestAnimationFrame(animate);
obst.update(-1, 0)
player1.build();
}
but obst var doesn't appear (but player1 appears)
class for obst:
class Obstacle {
constructor(x, y) {
this.x = x;
this.y = y;
}
build() {
var img = new Image();
img.src = 'assests/obst.png';
img.onload = () => {
ctx.drawImage(img, this.x, this.y, 60, 60);
}
}
update(x, y) {
this.x += x;
this.y += y;
this.build()
}
}
When I run the code without clearrect() syntax it shows as it should be.
Full code:
const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');
function animate() {
requestAnimationFrame(animate);
ctx.clearRect(0, 0, innerWidth, innerHeight);
obst.update(-1, 0)
player1.build();
}
class Player {
constructor(x, y, radius, color) {
this.x = x;
this.y = y;
this.radius = radius;
this.color = color;
}
build() {
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false)
ctx.fillStyle = this.color;
ctx.fill();
}
update(x, y) {
this.x += x
this.y += y
this.build()
}
}
class Obstacle {
constructor(x, y) {
this.x = x;
this.y = y;
}
build() {
var img = new Image();
img.src = 'assests/obst.png';
img.onload = () => {
ctx.drawImage(img, this.x, this.y, 60, 60);
}
}
update(x, y) {
this.x += x;
this.y += y;
this.build()
}
}
var obst = new Obstacle(canvas.width, canvas.height / 2 - 30)
obst.build()
var player1 = new Player(canvas.width / 2, canvas.height / 2, 30, 'blue');
player1.build();
animate();
The async task of loading the image should be removed from the update loop. Have the objects follow a pattern where building and updating / drawing are independent, and where building is async and happens once...
class Obstacle {
constructor(x, y) {
this.x = x;
this.y = y;
}
// don't use the object until this promise resolves
async build() {
var img = new Image();
img.src = 'assests/obst.png';
return new Promise(resolve => img.onload = resolve)
}
// call the method that draws current state "draw"
draw() {
ctx.drawImage(img, this.x, this.y, 60, 60);
}
// call the method that updates current state and draws "update"
update(x, y) {
this.x += x;
this.y += y;
this.draw()
}
}
class Player {
constructor(x, y, radius, color) {
this.x = x;
this.y = y;
this.radius = radius;
this.color = color;
}
// for symmetry, and maybe someday player will need to do async work here
async build() {
return Promise.resolve();
}
draw() {
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false)
ctx.fillStyle = this.color;
ctx.fill();
}
update(x, y) {
this.x += x
this.y += y
this.draw()
}
}
function animate() {
requestAnimationFrame(animate);
ctx.clearRect(0, 0, innerWidth, innerHeight);
obst.update(-1, 0)
player1.update(0, 1);
}
async function play() {
const obst = new Obstacle(canvas.width, canvas.height / 2 - 30)
await obst.build();
const player1 = new Player(canvas.width / 2, canvas.height / 2, 30, 'blue');
await player1.build();
animate();
}
play()
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