这里有一个更完整的例子：
//just a utility
function image(url, callback){
var img = new Image();
if(typeof callback === "function"){
img.onload = function(){
//just to ensure that the callback is executed async
setTimeout(function(){ callback(img, url) }, 0)
}
}
img.src = url;
return img;
}
//a utility to keep a value constrained between a min and a max
function clamp(v, min, max){
return v > min? v < max? v: max: min;
}
//returns a function that can be called with a keyCode or one of the known aliases
//and returns true||false wether the button is down
var isKeyDown = (function(aliases){
for(var i=256, keyDown=Array(i); i--; )keyDown[i]=false;
var handler = function(e){
keyDown[e.keyCode] = e.type === "keydown";
e.preventDefault(); //scrolling; if you have to suppress it
};
addEventListener("keydown", handler, false);
addEventListener("keyup", handler, false);
return function(key){
return(true === keyDown[ key in aliases? aliases[ key ]: key ])
}
})({
//some aliases, to be extended
up: 38,
down: 40,
left: 37,
right: 39
});
// Get the canvas and context
var canvas = document.getElementById("space");
canvas.width = 1920;
canvas.height = 700;
var ctx = canvas.getContext("2d");
//the acutal image is just a little-part of what defines your figue
var spaceperson = {
image: image("//i.imgur.com/Eh9Dpq2.png", function(img){
spaceperson.width = img.naturalWidth;
spaceperson.height = img.naturalHeight;
//start the rendering by calling update
update();
}),
//position
x: 60, y: 310,
width: 0, height: 0,
speed: 200 // 200px/s
};
var lastCall = 0; //to calculate the (real) time between two update-calls
//the render-fucntion
function update(){
//taking account for (sometimes changing) framerates
var now = Date.now(), time = lastCall|0 && (now-lastCall)/1000;
lastCall = now;
requestAnimationFrame(update);
var sp = spaceperson,
speed = sp.speed;
//checking the pressed buttons and calculates the direction
//two opposite buttons cancel out each other, like left and right
var dx = (isKeyDown('right') - isKeyDown('left')) * time,
dy = (isKeyDown('down') - isKeyDown('up')) * time;
//fix the speed for diagonals
if(dx && dy) speed *= 0.7071067811865475; // * 1 / Math.sqrt(2)
if(dx) { //there is some movement on the x-axes
sp.x = clamp(
//calculate the new x-Position
//currentPos + direction * speed
sp.x + dx * sp.speed,
//restraining the result to the bounds of the map
0, canvas.width - sp.width
);
}
//same for y
if(dy) sp.y = clamp(sp.y + dy * sp.speed, 0, canvas.height - sp.height);
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.drawImage(sp.image, sp.x, sp.y);
}
编辑：
一个简单的问题（我希望）；如果我以后要添加其他对象，我会在 update() 中检查冲突吗？
这仍然只是一个非常基本的示例。 update()-function 的主要目的应该是作为主事件循环。
触发所有必须按照必须发生的顺序在每一帧发生的事件。
var lastCall = 0;
function update(){
//I always want a next frame
requestAnimationFrame(update);
//handle timing
var now = Date.now(),
//time since the last call in seconds
//cause usually it's easier for us to think in
//tems like 50px/s than 0.05px/ms or 0.8333px/frame
time = lastCall|0 && (now-lastCall) / 1000;
lastCall = now;
movePlayer(time);
moveEnemies(time);
moveBullets(time);
collisionDetection();
render();
}
function render(){
ctx.clear(0, 0, canvas.width, canvas.height);
drawBackground(ctx);
for(var i=0; i<enemies.length; ++i)
enemies[i].render(ctx);
player.render(ctx);
}
并不是说您现在必须实现所有这些功能，而是让您了解可能的结构。
不要害怕将大任务（函数）分解为子任务。
给每个敌人一个move()-function 可能是有意义的，这样你就可以为每个敌人实现不同的运动模式，
或者你说每个敌人的模式都是（并且将是）相同的，最好是参数化的，然后你可以在一个循环中处理它。
渲染也是一样，正如我在代码的最后一部分中展示的那样。