问题描述
修改
这是一个JSFiddle,其中注释了“ tail”函数的代码。Solar System JSFiddle
我有一个正在处理的物体,其中一个物体绕着中心质量运行。那很好。
我现在正在尝试在该行星后面添加一条拖尾线或“尾巴”。 我的尾巴对象看起来像这样:
function Tail(maxLength){
this.points = [];
this.maxLength = maxLength;
this.addPoint = function(point){
for(var i = Math.min(maxLength,this.points.length); i < maxLength; i++){
this.points[i] = this.points[i - 1];
}
this.points[0] = point;
}
this.draw = function(ctx){
for(var i = 1; Math.min(maxLength,this.points.length); i++){
if(i < maxLength - 20){
ctx.globalAlpha = 1;
} else {
ctx.globalAlpha = (this.maxLength - i) / 20;
}
ctx.beginPath();
ctx.moveTo(this.points[i - 1].x,this.points[i - 1].y);
ctx.lineTo(this.points[i].x,this.points[i].y);
ctx.stroke();
}
ctx.globalAlpha = 1;
}
}
addPoint函数采用一个看起来像'{x:currentX,y:currentY}的对象 当调用对象时,currentX和currentY是对象的x和y点。
我不知道如何将点添加到点数组,然后根据这些坐标进行绘制。
解决方法
如果您用低不透明度的背景填充框架而不是清除它,则可以可视化对象的轨迹:
var canvas,width,height,ctx;
var bodies = [];
function init(){
canvas = document.getElementById("space-time");
width = window.innerWidth;
height = window.innerHeight;
canvas.width = width;
canvas.height = height;
ctx = canvas.getContext('2d');
createBodies();
setInterval(function(){
updateSystem();
updateBodies(0.01);
// ctx.clearRect(0,height);
// All magic here:
ctx.fillStyle = `rgba(0,.05)`;
ctx.shadowBlur = 0;
ctx.fillRect(0,canvas.width,canvas.height);
drawBodies();
},10);
}
function createBodies(){
bodies.push(new Body((this.width / 2) - 250,(this.height / 2) - 300,200,1,10,"#14c71d",true));
bodies.push(new Body((this.width / 2) + 100,(this.height / 2) + 100,350,5,"#de2d16",true));
bodies.push(new Body(this.width / 2,this.height / 2,1000000,30,"#FF8501",false)); //sun
}
function drawBodies(){
for(var i = 0; i < bodies.length; i++){
bodies[i].draw(ctx);
}
}
function updateBodies(dt){
for(var i = 0; i < bodies.length; i++){
bodies[i].update(dt);
}
}
function updateSystem(){
var G = 10;
for(var i = 0; i < bodies.length; i++){
for(var j = 0; j < bodies.length; j++){
if(i === j) continue;
var b1 = bodies[i];
var b2 = bodies[j];
var dist = Math.sqrt((b1.x - b2.x) * (b1.x - b2.x) + (b1.y - b2.y) * (b1.y - b2.y));
var force = G * (b1.m * b2.m) / dist / dist;
var nx = (b2.x - b1.x) / dist;
var ny = (b2.y - b1.y) / dist;
b1.ax += nx * force / b1.m;
b1.ay += ny * force / b1.m;
b2.ax -= nx * force / b2.m;
b2.ay -= ny * force / b2.m;
}
}
}
function Body(x,y,v,angle,mass,radius,color,hasTail){
this.x = x;
this.y = y;
this.vx = v * Math.cos(angle);
this.vy = v * Math.sin(angle);
this.m = mass;
this.radius = radius;
this.color = color;
this.ax = 0;
this.ay = 0;
this.update = function(dt){
this.vx += this.ax * dt;
this.vy += this.ay * dt;
this.x += this.vx * dt;
this.y += this.vy * dt;
this.ax = 0;
this.ay = 0;
}
this.draw = function(ctx){
ctx.beginPath();
ctx.arc(this.x,this.y,this.radius,6.28);
ctx.strokeStyle = this.color;
ctx.fillStyle = this.color;
ctx.shadowColor = this.color;
ctx.shadowBlur = 5;
ctx.fill();
}
}
#space-time {
background-color: #1a1a1c;
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<title>Solar System AJ</title>
</head>
<body onload="init();">
<canvas id="space-time"></canvas>
</body>
</html>
,
我已将您的版本修改为工作状态
var canvas,ctx;
var bodies = [];
function init(){
canvas = document.getElementById("space-time");
width = window.innerWidth;
height = window.innerHeight;
canvas.width = width;
canvas.height = height;
ctx = canvas.getContext('2d');
createBodies();
setInterval(function(){
updateSystem();
updateBodies(0.01);
ctx.clearRect(0,height);
drawBodies();
},hasTail){
this.x = x;
this.y = y;
this.vx = v * Math.cos(angle);
this.vy = v * Math.sin(angle);
this.m = mass;
this.radius = radius;
this.color = color;
this.ax = 0;
this.ay = 0;
if (hasTail) {
this.tail = new Tail(50);
}
this.update = function(dt){
this.vx += this.ax * dt;
this.vy += this.ay * dt;
this.x += this.vx * dt;
this.y += this.vy * dt;
this.ax = 0;
this.ay = 0;
if(this.tail){
this.tail.addPoint({x: this.x,y: this.y});
}
}
this.draw = function(ctx){
ctx.strokeStyle = this.color;
ctx.fillStyle = this.color;
ctx.shadowColor = this.color;
ctx.shadowBlur = 5;
if(this.tail){
this.tail.draw(ctx);
}
ctx.beginPath();
ctx.arc(this.x,6.28);
ctx.fill();
}
}
function Tail(maxLength){
this.points = [];
this.maxLength = maxLength;
this.addPoint = point => {
this.points = [point].concat(this.points).slice(0,this.maxLength);
}
this.draw = function(ctx){
for(var i = 1; i < this.points.length; i++){
ctx.beginPath();
if(i < maxLength - 20){
ctx.globalAlpha = 1;
} else {
ctx.globalAlpha = (this.maxLength - i) / 20;
}
ctx.moveTo(this.points[i - 1].x,this.points[i - 1].y);
ctx.lineTo(this.points[i].x,this.points[i].y);
ctx.stroke();
}
ctx.globalAlpha = 1;
}
}
#space-time {
background-color: #1a1a1c;
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<title>Solar System AJ</title>
</head>
<body onload="init();">
<canvas id="space-time"></canvas>
</body>
</html>