Apakah yang salah dengan pembolehubah dan nilai dir?

Question

window.onload=function(){varcanvas=document.getElementById("canvas");varcontext=canvas.getContext("2d");vart=Date.now();varx=0;vary=0;vardir=1; varspeed=150+Math.round(Math.random()

P粉781235689 · Answer

Saya mengubah suai logik anda sedikit dan memisahkan pengiraan kelajuan mendatar dan menegak:

function rnd(n){return Math.ceil(Math.random()*n)}
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
var t = Date.now();
const w=600,h=600;
var x = 10;
var y = 10;
var xspeed=150+rnd(75), yspeed=150+rnd(75);
function draw() { 
  var timePassed = (Date.now() - t) /1000;
  t = Date.now()
  context.clearRect(0, 0, w, h)
 
  context.beginPath();
  context.rect(x, y, 100, 60)
  context.fillStyle = "red"
  context.fill();

  if (y= h-60) yspeed=-yspeed;
  if (x= w-100) xspeed=-xspeed;
  x += xspeed*timePassed;
  y += yspeed*timePassed;
 
  window.requestAnimationFrame(draw);
}
draw();