I want to animate a rectangle on html canvas. when the user will click the canvas, the rectangle will start it's animation, and go to the clicked position. I used delta x and y to add and subtract pixels from the x and y position of the rectangle. But the problem with this solution is, I can't find a way to make the rectangle animate in a straight path.
My code:
'use strict'
const canvas = document.getElementById('canvas')
const ctx = canvas.getContext('2d')
const ratio = Math.ceil(window.devicePixelRatio)
let height = window.innerHeight
let width = window.innerWidth
canvas.height = height * ratio
canvas.width = width * ratio
canvas.style.height = `${height}px`
canvas.style.width = `${width}px`
ctx.setTransform(ratio, 0, 0, ratio, 0, 0)
let position = {
x: 0,
y: 0,
deltaX: 0,
deltaY: 0,
size: 20
}
let move = {
x: 0,
y: 0,
}
function animate() {
if (position.x === move.x && position.y === move.y) {
cancelAnimationFrame()
}
if (position.x !== move.x) {
ctx.fillRect(position.x, position.y, position.size, position.size)
position.x += position.deltaX
}
if (position.y !== move.y) {
ctx.fillRect(position.x, position.y, position.size, position.size)
position.y += position.deltaY
}
requestAnimationFrame(animate)
}
function moveTo(x, y) {
move.x = x
move.y = y
position.deltaX = position.x > x ? -1 : 1
position.deltaY = position.y > y ? -1 : 1
animate()
}
canvas.addEventListener('click', (event) => {
moveTo(event.clientX, event.clientY)
})
ctx.fillRect(position.x, position.y, position.size, position.size)<canvas id="canvas">
</canvas>If you click in the canvas the rectangle will start moving but it'll go in a weird path, I can't find a way to properly go straight at the clicked position.
see demo at Github page
Here is the sample Math from something I did a while ago...
If there is something you don't understand there ask
In your code it was moving "weird" because your delta values where always 1 or -1, no fractions, that limits the way the object can travel, instead we do our calculations using the angle.
const canvas = document.getElementById('canvas')
const ctx = canvas.getContext('2d')
let player = {
x: 0, y: 0, size: 10,
delta: { x: 0, y: 0 },
move: { x: 0, y: 0 }
}
function animate() {
let a = player.x - player.move.x;
let b = player.y - player.move.y;
if (Math.sqrt( a*a + b*b ) < 2) {
player.delta = { x: 0, y: 0 }
}
player.x += player.delta.x
player.y += player.delta.y
ctx.fillRect(player.x, player.y, player.size, player.size)
requestAnimationFrame(animate)
}
function moveTo(x, y) {
player.move.x = x
player.move.y = y
let angle = Math.atan2(y - player.y, x - player.x)
player.delta.x = Math.cos(angle)
player.delta.y = Math.sin(angle)
}
canvas.addEventListener('click', (event) => {
moveTo(event.clientX, event.clientY)
})
animate()<canvas id="canvas"></canvas>