虫子的图像只出现在一个地方,即 x = 0,y = 0。
var canvas = document.querySelector('canvas');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var c = canvas.getContext('2d');
var bugSmashed = 0;
//rendering background image
function renderImage()
{
var backImage = new Image();
backImage.src = "jungle.jpg"
backImage.onload = function(){
c.drawImage(backImage,0,0,canvas.width,canvas.height)}
}
renderImage();
//Making a bug
class Bug {
constructor(x,y){
this.x = x;
this.y = y;
}
renderBug(){
var bugImage = new Image();
bugImage.src = "bug.png";
bugImage.onload = function(){
c.drawImage(bugImage,this.x,this.y,65,65)}}
}
试图让 bug 随机出现在画布上
var interval = setInterval(function(){
var x = 32+Math.random()*(canvas.width-64);
var y = 32+Math.random()*(canvas.height-64);
var aBug = new Bug(x,y);
aBug.renderBug();}, 2000);
我确定我遗漏了一些东西。任何帮助表示赞赏。谢谢
答案 0 :(得分:1)
我发现了您的问题:this
在 function
中改变了它的含义。所以当你使用:
function(){c.drawImage(bugImage,this.x,this.y,65,65)}
this
不再指 aBug
! (它会改为引用全局 Window
对象。)您可以改用粗箭头语法(保留 this
):
() => c.drawImage(bugImage,this.x,this.y,65,65)
我不鼓励您使用的另一种非常丑陋的方法是创建对 this
的新引用,然后在您的函数中使用该引用:
let that = this;
function(){ c.drawImage(bugImage, that.x, that.y, 65, 65); };
或者你可以简化你的代码,让它掩盖 onload
逻辑,让你首先避免将 c.drawImage
包装在函数中(注意出现的方块是一个可公开寻址的图像) :
var canvas = document.querySelector('canvas');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var c = canvas.getContext('2d');
//Making a bug
let bugImg = new Image();
bugImg.src = "https://th.bing.com/th/id/OIP.pXD0MAw4LeAcVrt3qRiEfwAAAA?pid=ImgDet&rs=1";
class Bug {
constructor(x,y){
this.x = x;
this.y = y;
}
renderBug(){
c.drawImage(bugImg, this.x, this.y, 65, 65);
}
}
var interval = setInterval(function(){
var x = 32 + Math.random()* (canvas.width - 64);
var y = 32 + Math.random()* (canvas.height - 64);
var aBug = new Bug(x, y);
aBug.renderBug();
}, 500);
<canvas id="canvas" width="100" height="100"></canvas>