我正在写一个面向对象风格的javasscript演示——只是为了画一堆在屏幕上移动的球。没有什么新奇的,没有碰撞检测或任何事情。认为我的Ball.js类很好是安全的。
我的问题是:我应该在哪里叫球。draw(上下文)?按照我设置的方式将球绘制到屏幕上的唯一方法似乎是在generateBalls()中进行调用。但这意味着每个球只抽一次。
所以,如果有人能指出我在这里的错误,我真的很感激。这不是家庭作业,只是想更好地处理javascript和画布。
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
<script src="ball.js"></script>
<script src="utils.js"></script>
...
<canvas id="canvas" width="600" height="480"></canvas>
<script type="text/javascript">
window.addEventListener('load', eventWindowLoaded, false);
function eventWindowLoaded() {
canvasApp();
}
function canvasSupport() {
return true;
}
function canvasApp() {
if(!canvasSupport()) {
return;
}
}
console.log("app entered");
var numBalls = 45;
//var numBalls = demo.numberofballs.value;
var maxSize = 8;
var minSize = 5;
var maxSpeed = maxSize + 5;
var balls = new Array();
var tempBall;
var tempX;
var tempY;
var tempSpeed;
var tempAngle;
var tempRadius;
var tempRadians;
var tempXunits;
var tempYunits;
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
generateBalls();
setInterval(drawScreen, 33);
function generateBalls() {
console.log("Make some balls");
for(var index = 0; index < numBalls; index++) {
var tempRadius = Math.floor(Math.random()*maxSize)+minSize;
var ball = new Ball(tempRadius, "#000000");
ball.x = tempRadius * 2 + (Math.floor(Math.random()*canvas.width) - tempRadius * 2);
ball.y = tempRadius * 2 + (Math.floor(Math.random()*canvas.height) - tempRadius * 2);
ball.speed = maxSpeed - tempRadius;
ball.angle = Math.floor(Math.random()*360);
ball.dx = Math.cos(tempRadians) * tempSpeed;
ball.dy = Math.sin(tempRadians) * tempSpeed;
// here outputted balls but a stupid place to put it LOL
balls.push(ball);
}
}
function drawScreen() {
console.log("draw screen");
// loop through all balls and adjust their position
// a BallManager could do this more cleanly
for(var index = 0; index < balls.length; index++) {
context.fillStyle="#EE00EE";
context.fillRect(0,0,canvas.width, canvas.height);
// Box
context.strokeStyle = "#ff0043";
context.strokeRect(1,1,canvas.width-2, canvas.height-2);
// place balls
context.fillStyle = "#ff8783";
console.log("ball mover loop in drawscreen");
// no var ball now
ball = balls[index];
ball.x += ball.dx;
ball.y += ball.dy;
ball.draw(context);
//checkBoundaries(balls[index]);
if(ball.x > canvas.width || ball.x < 0) {
ball.angle = 180 - ball.angle;
updateBall(ball);
} else if(ball.y > canvas.height || ball.y < 0) {
ball.angle = 360 - ball.angle;
updateBall(ball);
//ball.draw(context);
}
}
}
//function checkBoundaries(ball) {
//console.log("Check Bounds: " + " " + "ball.x: " + ball.x + " " + //"ball.y: " + ball.y);
//}
function updateBall(ball) {
ball.radians = ball.angle * Math.PI / 180;
ball.dx = Math.cos(ball.radians) * ball.speed;
ball.dy = Math.sin(ball.radians) * ball.speed;
//ball.draw(context);
}
</script>
</body>
</html>
谢谢你的建议,Marc
您的示例包含多个错误,请检查修改后的代码。它是有效的,但你必须扩展并更正它。
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
<script type="text/javascript">
// next lines is a Ball() implementation code
Ball = function(radius,color) {
this.radius=radius;
this.color=color;
};
Ball.prototype.x=0;
Ball.prototype.y=0;
Ball.prototype.speed=0;
Ball.prototype.angle=0;
Ball.prototype.dx=0;
Ball.prototype.dy=0;
Ball.prototype.radius=10;
Ball.prototype.color="#000";
Ball.prototype.draw=function() {
context.beginPath();
context.arc(this.x,this.y,this.radius,0,Math.PI*2,true);
context.lineWidth = 5;
context.strokeStyle = this.color; // line color
context.stroke();
context.closePath();
};
window.addEventListener('load', eventWindowLoaded, false);
function eventWindowLoaded() {
canvasApp();
//console.log("app entered");
window.canvas = document.getElementById("canvas");
window.context = canvas.getContext("2d");
generateBalls();
// if you want to use setInterval() instead replace next line
setTimeout(drawScreen, 33);
}
function canvasSupport() {
return true;
}
function canvasApp() {
if(!canvasSupport()) {
return;
}
}
var numBalls = 45;
//var numBalls = demo.numberofballs.value;
var maxSize = 8;
var minSize = 5;
var maxSpeed = maxSize + 5;
var balls = new Array();
var tempBall;
var tempX;
var tempY;
var tempSpeed;
var tempAngle;
var tempRadius;
var tempRadians;
var tempXunits;
var tempYunits;
function generateBalls() {
//console.log("Make some balls");
for(var index = 0; index < numBalls; index++) {
var tempRadius = Math.floor(Math.random()*maxSize)+minSize;
var tempRadians = Math.random()*Math.PI;
var tempSpeed = 10;
var ball = new Ball(tempRadius, "#000000");
ball.x = tempRadius * 2 + (Math.floor(Math.random()*canvas.width) - tempRadius * 2);
ball.y = tempRadius * 2 + (Math.floor(Math.random()*canvas.height) - tempRadius * 2);
ball.speed = maxSpeed - tempRadius;
ball.angle = Math.floor(Math.random()*360);
ball.dx = Math.cos(tempRadians) * tempSpeed;
ball.dy = Math.sin(tempRadians) * tempSpeed;
// here outputted balls but a stupid place to put it LOL
balls.push(ball);
}
}
function drawScreen() {
console.log("draw screen");
context.fillStyle="#EE00EE";
context.fillRect(0,0,canvas.width, canvas.height);
// Box
context.strokeStyle = "#ff0043";
context.strokeRect(1,1,canvas.width-2, canvas.height-2);
// loop through all balls and adjust their position
// a BallManager could do this more cleanly
for(var index = 0; index < balls.length; index++) {
// place balls
context.fillStyle = "#008700";
//console.log("ball mover loop in drawscreen");
// no var ball now
ball = balls[index];
ball.x += ball.dx;
ball.y += ball.dy;
ball.draw(context);
//checkBoundaries(balls[index]);
if(ball.x > canvas.width || ball.x < 0) {
ball.angle = 180 - ball.angle;
updateBall(ball);
} else if(ball.y > canvas.height || ball.y < 0) {
ball.angle = 360 - ball.angle;
updateBall(ball);
//ball.draw(context);
}
}
// if you want to use setInterval() instead remove next line
setTimeout(drawScreen, 33);
}
//function checkBoundaries(ball) {
//console.log("Check Bounds: " + " " + "ball.x: " + ball.x + " " + //"ball.y: " + ball.y);
//}
function updateBall(ball) {
ball.radians = ball.angle * Math.PI / 180;
ball.dx = Math.cos(ball.radians) * ball.speed;
ball.dy = Math.sin(ball.radians) * ball.speed;
//ball.draw(context);
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="480" style="background:red;"></canvas>
</body>
</html>
http://jsfiddle.net/QVgZx/2/
只需坏死线程,即可为新到画布的用户添加一点更新:
Stan建议创建一个函数,在代码中的一个位置绘制每个球;这是好的,原因有很多,它使动画更流畅,代码更容易调试/维护。
然而,当谈到使用setInterval来触发这个。。。尽管如此,当斯坦写这本书的时候,这很可能是一种常见的做法
然而,现在我们使用requestAnimationFrame。
这将使您的绘画与浏览器的其他部分同步。
这让你的代码运行得更快,因为每次浏览器绘制东西时,它都必须再次浏览整个页面,以确定所有东西的去向,以防有东西移动。
使用setInterval并不能保证它何时会启动,当然也不会使它与浏览器的屏幕刷新同步。
这意味着它画了一点,重新配置页面,再画一点,再重新配置,再画一些。。。一次又一次。这非常糟糕,而且非常缓慢。
然而,使用requestAnimationFrame,浏览器可以在任何时候重新绘制屏幕时调用您的函数。。。这意味着一次重画和一次刷新。
速度快得多,清洁得多。
它的工作原理略有不同,但实际上非常简单。
requestAnimationFrame(redraw);
这会将您的函数"rewrap"注册到requestAnimationFrame中,这样下次浏览器想要重新绘制窗口时,就会调用您的函数。
问题是它只会调用你的函数一次。。。这样一来,它就像一个setTimeout,而不是一个setInterval。
这样,就不需要绕过计时器变量来停止动画;它将停止,因为它不再被调用。
然而,为了确保动画继续运行,只需将相同的调用放在重绘函数的底部即可:
function redraw()
{
var blah, blahblah;
...
requestAnimationFrame(redraw);
}
你也可以有条件地设置它,运行你的动画直到它完成,然后停止:
function redraw()
{
...
if (!finished) requestAnimationFrame(redraw);
}
Mozilla参考HERE,Paul Irish HERE和Chris Coyer HERE。