[英]Making mouse position (0, 0) the center of the canvas
所以我最近一直在搞亂html5畫布並試圖弄清楚如何制作一個粒子系統。 雖然它確實有效但我想制作vx =鼠標坐標(特別是x),但它們從中心開始。
我的意思是,基本上如果光標位於畫布的中心,那么vx將等於0,如果光標位於畫布中心的右側,則它具有正的鼠標坐標(如果光標是從畫布中心左側它有負鼠標坐標)。
一旦完成,我只會做p.speed += p.vx
這是我的javascript:
window.onload = function(){
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var W = window.innerWidth, H = window.innerHeight;
canvas.width = W;
canvas.height = H;
var particles = [];
var particle_count = 100;
for(var i = 0; i < particle_count; i++)
{
particles.push(new particle());
}
function particle()
{
this.vx = -1 + Math.random() * 2;
this.speed = {x: 0, y: -15+Math.random()*10};
this.location = {x: W/2, y: H/2};
this.radius = 5+Math.random()*10;
this.life = 20+Math.random()*10;
this.remaining_life = this.life;
this.r = Math.round(Math.random()*255);
this.g = Math.round(Math.random()*55);
this.b = Math.round(Math.random()*5);
}
function draw()
{
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "black";
ctx.fillRect(0, 0, W, H);
ctx.globalCompositeOperation = "lighter";
for(var i = 0; i < particles.length; i++)
{
var p = particles[i];
ctx.beginPath();
p.opacity = Math.round(p.remaining_life/p.life*100)/100
var gradient = ctx.createRadialGradient(
p.location.x, p.location.y, 0, p.location.x, p.location.y, p.radius);
gradient.addColorStop(0, "rgba("+p.r+", "+p.g+", "+p.b+", "+p.opacity+")");
gradient.addColorStop(0.5, "rgba("+p.r+", "+p.g+", "+p.b+", "+p.opacity+")");
gradient.addColorStop(1, "rgba("+p.r+", "+p.g+", "+p.b+", 0)");
ctx.fillStyle = gradient;
ctx.arc(p.location.x, p.location.y, p.radius, Math.PI*2, false);
ctx.fill();
p.remaining_life--;
p.radius--;
p.location.x += p.speed.x += p.vx;
p.location.y += p.speed.y;
if(p.remaining_life < 0 || p.radius < 0) {
particles[i] = new particle();
}
}
}
setInterval(draw, 33); }
這是我的codepen 。
示例 :
var cx = canvas.width * 0.5;
var cy = canvas.height * 0.5;
ctx.translate(cx, cy); // translate globally once
對於每個鼠標坐標補償翻譯位置:
var pos = getMousePosition(evt); // see below
var x = pos.x - cx;
var y = pos.y - cy;
要調整鼠標位置:
function getMousePosition(evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
}
}
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