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javascript - 如何停止我的尾随线导致对象由于数组大小而变慢

问题描述

随着阵列变大，我在画布上的方形物体会急剧变慢。该数组用于存储先前的 x,y 位置，然后尾随线使用这些位置来绘制自身。

有没有办法让我的对象以相同的速度移动，同时保持整个尾随线，即我不希望尾随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>

标签： javascriptarrayscanvas

解决方案

您可以进行有益的优化。目前，您在每次更新时都向 myArrayX 和 myArrayY 添加数字。这意味着如果你的方格根本不动，你将有很多无用的数据，因为位置没有改变。

我建议：如果 x 或 y 位置发生变化，只需将元素放入数组即可。这可以通过设置两个全局变量来完成，这些变量保存最后的 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>

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