随着数组变大，我在 Canvas 上的方形对象速度急剧下降。该数组用于存储之前的 x,y 位置，然后拖尾线使用这些位置绘制自身。
有没有办法让我的对象以相同的速度移动，同时保持整个拖尾线，即我不希望拖尾线在任何时间点褪色/消失。
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
border:1px solid #d3d3d3;
background-color: #f1f1f1;
}
</style>
</head>
<body onload="startGame()">
<script>
var myGamePiece;
var myArrayX = [];
var myArrayY = [];
function startGame() {
myGamePiece = new component(30, 30, "red", 10, 120);
myGameArea.start();
}
var myGameArea = {
canvas : document.createElement("canvas"),
start : function() {
this.canvas.width = 480;
this.canvas.height = 270;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.interval = setInterval(updateGameArea, 20);
},
clear : function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function component(width, height, color, x, y) {
this.width = width;
this.height = height;
this.speedX = 0;
this.speedY = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = myGameArea.context;
ctx.fillStyle = color;
ctx.fillRect(this.x, this.y, this.width, this.height);
// testing:
ctx.beginPath();
ctx.strokeStyle = "red";
ctx.setLineDash([5,5]);
ctx.moveTo(10, 120);
var arrLength = myArrayX.length;
for(var i=0; i<arrLength;i+=1){
ctx.lineTo(myArrayX[i], myArrayY[i]);
ctx.stroke();
}
}
this.newPos = function() {
this.x += this.speedX;
this.y += this.speedY;
myArrayX.push(this.x);
myArrayY.push(this.y);
}
//end test
}
function updateGameArea() {
myGameArea.clear();
myGamePiece.newPos();
myGamePiece.update();
document.getElementById("test").innerHTML = "size of array: " + (myArrayX.length -1).toString()
}
window.addEventListener('keydown', function(e) {
switch(e.keyCode){
case 37:
myGamePiece.speedX = -1;
break;
case 38:
myGamePiece.speedY = -1;
break;
case 39:
myGamePiece.speedX = 1;
break;
case 40:
myGamePiece.speedY = 1;
break;
}
})
window.onkeyup = function() {
switch(window.event.keyCode){
case 37:
myGamePiece.speedX = 0;
break;
case 38:
myGamePiece.speedY = 0;
break;
case 39:
myGamePiece.speedX = 0;
break;
case 40:
myGamePiece.speedY = 0;
break;
}
}
</script>
<p id="test"></p>
</body>
</html>
最佳答案
您可以进行有益的优化。目前，您在每次更新时都会向 myArrayX 和 myArrayY 添加数字。这意味着如果您的正方形根本没有移动，您将拥有大量无用数据，因为位置没有改变。
我建议:如果 x 或 y 位置发生变化，则将元素放入数组。这可以通过设置两个全局变量来完成，这两个变量保存最后的 x 和 y 坐标，并在更新数组之前与它们进行比较。
看看这个:
var myGamePiece;
var myArrayX = [];
var myArrayY = [];
var oldX = 0;
var oldY = 0;
function startGame() {
myGamePiece = new component(30, 30, "red", 10, 120);
myGameArea.start();
}
var myGameArea = {
canvas: document.createElement("canvas"),
start: function() {
this.canvas.width = 480;
this.canvas.height = 270;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.interval = setInterval(updateGameArea, 20);
},
clear: function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function component(width, height, color, x, y) {
this.width = width;
this.height = height;
this.speedX = 0;
this.speedY = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = myGameArea.context;
ctx.fillStyle = color;
ctx.fillRect(this.x, this.y, this.width, this.height);
// testing:
ctx.beginPath();
ctx.strokeStyle = "red";
ctx.setLineDash([5, 5]);
ctx.moveTo(10, 120);
var arrLength = myArrayX.length;
for (var i = 0; i < arrLength; i += 1) {
ctx.lineTo(myArrayX[i], myArrayY[i]);
ctx.stroke();
}
}
this.newPos = function() {
this.x += this.speedX;
this.y += this.speedY;
if (this.x != oldX || this.y != oldY) {
myArrayX.push(this.x);
myArrayY.push(this.y);
}
oldX = this.x;
oldY = this.y;
}
//end test
}
function updateGameArea() {
myGameArea.clear();
myGamePiece.newPos();
myGamePiece.update();
document.getElementById("test").innerHTML = "size of array: " + (myArrayX.length - 1).toString()
}
window.addEventListener('keydown', function(e) {
switch (e.keyCode) {
case 37:
myGamePiece.speedX = -1;
break;
case 38:
myGamePiece.speedY = -1;
break;
case 39:
myGamePiece.speedX = 1;
break;
case 40:
myGamePiece.speedY = 1;
break;
}
})
window.onkeyup = function() {
switch (window.event.keyCode) {
case 37:
myGamePiece.speedX = 0;
break;
case 38:
myGamePiece.speedY = 0;
break;
case 39:
myGamePiece.speedX = 0;
break;
case 40:
myGamePiece.speedY = 0;
break;
}
}
startGame();canvas {
border: 1px solid #d3d3d3;
background-color: #f1f1f1;
}<p id="test"></p>关于javascript - 如何停止我的尾随线导致对象因数组大小而减慢，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56184965/