连接移动弧线的 JavaScript 不需要的线

Question

所以我有这个基本的脚本，它使4个圆围绕一个中心移动，我放了两个圆圈，这是圆圈遵循的路线。问题是有奇怪的不需要的线将圆圈连接到静止的圆圈。我认为这可能是因为圆圈ctx.arc(cx, cy, 200, 200, 0, 2 * Math.PI);的线在绘制功能内。有谁知道如何解决这个问题？(将静止圆圈放置在绘制功能之外会导致它们在清除画布时消失。

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var w = canvas.width;
var h = canvas.height;
var dd = 3;
var dd2 = 3;
var dd3 = 3;
var dd4 = 3;
var angle = 0;
var angle2 = 0;
var angle3 = 0;
var angle4 = 0;
var cx = 1000;
var cy = 1000;
var radius = 200;
var radius2 = 300;
var radius3 = 400;
var radius4 = 500;
var fps = 100;
ctx.fillStyle = "yellow";
ctx.strokeStyle = "skyblue";
(function () {
"use strict";
function draw(x, y) {
ctx.save();
ctx.clearRect(0, 0, w, h);
ctx.beginPath();
ctx.arc(cx, cy, 75, 75, 0, 2 * Math.PI);
ctx.fillStyle = "lightgray";
ctx.arc((x - 50 / 2) + 25, (y - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.arc(cx, cy, 200, 200, 0, 2 * Math.PI);
ctx.stroke();
ctx.closePath();
ctx.restore();
}
function draw1(x1, y1) {
ctx.save();
ctx.beginPath();
ctx.fillStyle = "orange";
ctx.arc((x1 - 50 / 2) + 25, (y1 - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.arc(cx, cy, 300, 300, 0, 2 * Math.PI);
ctx.stroke();
ctx.closePath();
ctx.restore();
}   
function draw2(x2, y2) {
ctx.save();
ctx.beginPath();
ctx.fillStyle = "blue";
ctx.arc((x2 - 50 / 2) + 25, (y2 - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.arc(cx, cy, 400, 400, 0, 2 * Math.PI);
ctx.stroke();
ctx.closePath();
ctx.restore();
}
function draw3(x3, y3) {
ctx.save();
ctx.beginPath();
ctx.fillStyle = "red";
ctx.arc((x3 - 50 / 2) + 25, (y3 - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.arc(cx, cy, 500, 500, 0, 2 * Math.PI);
ctx.stroke();
ctx.closePath();
ctx.restore();
}
window.requestAnimFrame = (function (callback) {
return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function (callback) {
window.setTimeout(callback, 1000 / fps);
};
}());

function animate() {
setTimeout(function () {
requestAnimFrame(animate);
ctx.beginPath();
angle += Math.acos(1 - Math.pow(dd / radius, 2) / 2);
var newX = cx + radius * Math.cos(angle),
newY = cy + radius * Math.sin(angle),
newX1 = cx + radius2 * Math.cos(angle2),
newY1 = cy + radius2 * Math.sin(angle2),
newX2 = cx + radius3 * Math.cos(angle3),
newY2 = cy + radius3 * Math.sin(angle3),
newX3 = cx + radius4 * Math.cos(angle4),
newY3 = cy + radius4 * Math.sin(angle4);
draw(newX, newY);
ctx.arc(cx, cy, radius, 0, Math.PI * 2);
ctx.closePath();
ctx.beginPath();
angle2 += Math.acos(1 - Math.pow(dd2 / radius2, 2) / 2);
draw1(newX1, newY1);
ctx.arc(cx, cy, radius2, 0, 2 * Math.PI);
ctx.closePath();
ctx.beginPath();
angle3 += Math.acos(1 - Math.pow(dd3 / radius3, 2) / 2);
draw2(newX2, newY2);
ctx.arc(cx, cy, radius3, 0, 2 * Math.PI);
ctx.closePath();
ctx.beginPath();
angle4 += Math.acos(1 - Math.pow(dd4 / radius4, 2) / 2);
draw3(newX3, newY3);
ctx.arc(cx, cy, radius4, 0, 2 * Math.PI);
ctx.closePath();
}, 1000 / fps);
}
animate();
}());

Answer 1

你必须使用ctx.beginPath()，ctx.closePath()和ctx.stroke()你创建的每arc，否则它会用线条连接它们(如果你正在画画并且不允许将铅笔从纸上取下来，你自己也必须这样做(：

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var w = canvas.width;
var h = canvas.height;
var dd = 3;
var dd2 = 3;
var dd3 = 3;
var dd4 = 3;
var angle = 0;
var angle2 = 0;
var angle3 = 0;
var angle4 = 0;
var cx = 1000;
var cy = 1000;
var radius = 200;
var radius2 = 300;
var radius3 = 400;
var radius4 = 500;
var fps = 100;
ctx.fillStyle = "yellow";
ctx.strokeStyle = "skyblue";
(function () {
"use strict";
function draw(x, y) {
ctx.save();
ctx.clearRect(0, 0, w, h);
ctx.beginPath();
ctx.arc(cx, cy, 75, 75, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.fillStyle = "lightgray";
ctx.beginPath();
ctx.arc((x - 50 / 2) + 25, (y - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.arc(cx, cy, 200, 200, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.restore();
}
function draw1(x1, y1) {
ctx.save();
ctx.fillStyle = "orange";
ctx.beginPath();
ctx.arc((x1 - 50 / 2) + 25, (y1 - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.arc(cx, cy, 300, 300, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.restore();
}   
function draw2(x2, y2) {
ctx.save();
ctx.fillStyle = "blue";
ctx.beginPath();
ctx.arc((x2 - 50 / 2) + 25, (y2 - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.arc(cx, cy, 400, 400, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.restore();
}
function draw3(x3, y3) {
ctx.save();
ctx.fillStyle = "red";
ctx.beginPath();
ctx.arc((x3 - 50 / 2) + 25, (y3 - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.arc(cx, cy, 500, 500, 0, 2 * Math.PI);
ctx.closePath();
ctx.stroke();
ctx.restore();
}
window.requestAnimFrame = (function (callback) {
return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function (callback) {
window.setTimeout(callback, 1000 / fps);
};
}());
function animate() {
setTimeout(function () {
requestAnimFrame(animate);
angle += Math.acos(1 - Math.pow(dd / radius, 2) / 2);
var newX = cx + radius * Math.cos(angle),
newY = cy + radius * Math.sin(angle),
newX1 = cx + radius2 * Math.cos(angle2),
newY1 = cy + radius2 * Math.sin(angle2),
newX2 = cx + radius3 * Math.cos(angle3),
newY2 = cy + radius3 * Math.sin(angle3),
newX3 = cx + radius4 * Math.cos(angle4),
newY3 = cy + radius4 * Math.sin(angle4);
draw(newX, newY);
ctx.arc(cx, cy, radius, 0, Math.PI * 2);
angle2 += Math.acos(1 - Math.pow(dd2 / radius2, 2) / 2);
draw1(newX1, newY1);
ctx.arc(cx, cy, radius2, 0, 2 * Math.PI);
angle3 += Math.acos(1 - Math.pow(dd3 / radius3, 2) / 2);
draw2(newX2, newY2);
ctx.arc(cx, cy, radius3, 0, 2 * Math.PI);
angle4 += Math.acos(1 - Math.pow(dd4 / radius4, 2) / 2);
draw3(newX3, newY3);
ctx.arc(cx, cy, radius4, 0, 2 * Math.PI);
}, 1000 / fps);
}
animate();
}());

<canvas id="canvas" width="2000" height="2000"></canvas>

例如，我更改了以下内容：

ctx.beginPath();
ctx.arc(cx, cy, 75, 75, 0, 2 * Math.PI);
ctx.fillStyle = "lightgray";
ctx.arc((x - 50 / 2) + 25, (y - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.arc(cx, cy, 200, 200, 0, 2 * Math.PI);
ctx.stroke();
ctx.closePath();

进入这个：

ctx.beginPath();
ctx.arc(cx, cy, 75, 75, 0, 2 * Math.PI);
ctx.closePath(); //Added
ctx.stroke();    //Added
ctx.fillStyle = "lightgray";
ctx.beginPath(); //Added
ctx.arc((x - 50 / 2) + 25, (y - 30 / 2) + 15, 25, 25, 0, 2 * Math.PI);
ctx.closePath(); //Added
ctx.stroke();    //Added
ctx.beginPath(); //Added
ctx.arc(cx, cy, 200, 200, 0, 2 * Math.PI);
ctx.closePath(); //Reversed order (doesn't really matter, but looks better IMO)
ctx.stroke();    //Reversed order (doesn't really matter, but looks better IMO)