Question

I have a small project in my webprogramming course where I am supposed to make a small game in javascript. This is the game: two cannons are fixed on opposing ends of the game space. The cannons take turns shooting at each other, and the player tilts the cannon to some degree and chooses a force to shoot the cannonball with. There s a bunch of other stuff I m thinking of that will be added if there s time.

我找到了一个不错的网站,"http://www.rodedev.com/tutorics/gamephysics/" rel="nofollow">http://www.rodedev.com/tutors/gamephysics/ ,让我能接受2D物理,我做了一些测试,见下面的代码。但我确实有两个大问题:

Non-flat floor/ground.
Rotation!

Right now the script is only checking for the style.top value of the floorDiv, so the box will always "land" on this row of pixels. If I want to have variable-height terrain, this won t suffice. Any ideas from you guys on how this could be accomplished? Is there anyway to check the color at a specific pixel? If so I could check for non-sky or ground colored pixels and make this the landing critera.

I need to rotate the cannon so players can adjust their aim! I m thinking I ll make two different cannon objects, the cannon "base" and the cannon barrel. Then I could just rotate the cannon barrel when the player presses a key. Unfortunately rotation seems to be hard in webprogramming. I found this jquery plugin, at http://code.google.com/p/jquery-rotate/, but I m not getting it to work quite as I would like. Even though I ve made sure the cannonball is centered in the picture there is also some translation, not just rotation. I suppose this might be because the picture doesn t rotate about it s center? See the rotation test code below (you ll have to download the rotation plugin if you want to try the code). I suppose I could just make a picture for each angle but that seems kind of wasteful since there s no actual visual change to the cannon otherwise.

Also, if I want to animate several objects at the same time, do you think I should just change all the objects in the same gameloop function? Any ideas on this?

以下是物理测试的代码。

CSS 文件

#moveDiv {
    position:absolute;
    width:100px;
    height:100px;
    background-color:#000;
}

#floorDiv {
    position:absolute;
    width:800px;
    height:1px;
    background-color:#2E2;
}

table {
text-align:right;

}
table input {
    width:35px;
}

HTML 文件

<script type="text/javascript">
//global vars
var gravity = 0.5;
var friction = 0.5;
var moving = false;
var moveDiv;
var floorDiv;
var yPos;
var xPos;
var floorPos;
var velocity_y = 0;
var velocity_x = 0;
</script>
</head>

<body onload="initialize();">
<input type="button" value="fall" onclick="fall();"></button>
<input type="button" value="Push" onclick="push();"></button>
<input type="button" value="reset" onclick="reset();"></button>

<table>
<tr>
<td>Angle: <input type="text" value="45" id="angle" /></td>
<td>Speed: <input type="text" value="10" id="speed"/></td>
</tr>
<tr>
<td>Gravity: <input type="text" value="0.5" id="gravity" /></td>
<td>Friction: <input type="text" value="0.5" id="friction" /></td>
</table>

<div id="moveDiv"></div>
<div id="floorDiv"></div>
</body>
</html>

js 文件

function initialize() {
    moveDiv = document.getElementById( moveDiv );
    floorDiv = document.getElementById( floorDiv ); 

    moveDiv.style.left=400;
    moveDiv.style.top=50;

    floorDiv.style.left=200;
    floorDiv.style.top=400;
}//end initialize

function fall() 
{
    moving=true;
    var angle = 275;
    var rad = angle / (Math.pi * 2);
    var scale_x = Math.cos(rad);
    var scale_y = Math.sin(rad);

    var moveDivSpeed = 0;

    gameLoop();

}//end fall

function push() 
{
    moving=true;
    var angle = document.getElementById( angle ).value;
    var rad = angle / (Math.PI * 2);
    var scale_x = Math.cos(rad);
    var scale_y = Math.sin(rad);
    var moveDivSpeed = document.getElementById( speed ).value;
    friction = document.getElementById( friction ).value;
    gravity = document.getElementById( gravity ).value;
    velocity_x = moveDivSpeed*scale_x;
    console.log("original velocity_x is " + velocity_x);
    velocity_y = moveDivSpeed*scale_y;
    gameLoop();
}

function gameLoop () {
    //console.log("gameLoop start");
    var len = moveDiv.style.top.length;
    var presentTop = parseInt(moveDiv.style.top.substr(0, len-2));

    var lenX = moveDiv.style.left.length;
    var presentLeft = parseInt(moveDiv.style.left.substr(0, lenX-2));

    var len2 = floorDiv.style.top.length;
    var floorTop = parseInt(floorDiv.style.top.substr(0, len2-2));

    if (moving == true) 
    {
        velocity_y -= gravity;

        if ((presentTop+100) - velocity_y < floorTop) 
        { //if moveDiv hasn t hit the floor yet...
            moveDiv.style.top = presentTop - velocity_y;
            moveDiv.style.left = presentLeft + velocity_x;
        }
        else if (presentTop + 100 == floorTop) //if moveDiv is ON the floor
        {
            velocity_x = velocity_x*(1-friction);
            moveDiv.style.left = presentLeft + velocity_x;
            console.log("on the floor");
            console.log("friction is " + friction);
            console.log(" and velocity_x is " + velocity_x);
            console.log("moveDiv.style.left is " +moveDiv.style.left);

            if (velocity_x <= 1)
            {
                console.log("stopped moving");
                moving = false;
            }

        }
        else //if moveDiv will hit the floor/go through the floor this time
        {
            var diff = floorTop - (presentTop + 100);
            moveDiv.style.top = presentTop + diff;
            moveDiv.style.left = presentLeft + velocity_x;
        }
    }
    else if (moving == false) 
    {
        clearTimeout(runAgain);
        console.log("else if moving == false");
        return false;
    }

    var runAgain = setTimeout("gameLoop()", 5);
    //console.log("end of gameLoop");
    return false;
}//end gameLoop

function reset () {
    moving = false;

    moveDiv.style.left=400;
    moveDiv.style.top=50;

    floorDiv.style.left=200;
    floorDiv.style.top=400;
}//end reset

旋转测试的代码( 只有 html 文件及旋转插件)

<html>
<head>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript" src="jquery.rotate.1-1.js"></script>
<script type="text/javascript">
    $(document).ready(function() {

        $("#hide").click(function() {
            $("p").hide(500);
            $(".box").animate({height:300, opacity:0}, 1000);
        });

        $("#show").click(function() {
            $("p").show(500);
            $(".box").animate({height:100, opacity:100}, 1000);
        });

        $(".box").mouseenter(function() {
            $(".box").animate({height:300, opacity:0}, 500);
        });

        $(".box").mouseleave(function() {
            $(".box").animate({height:100, opacity:10}, 1000);
        });

        $("#move").click(function() {
            $("#grey").animate({left: -300, top: -100}, 1000)
            .animate({left: -600, top: 200}, 1000);
        });

        $("#cannonball").click(function() {
            $("#cannonball").animate({"left": "+=300", "top": "-=100"}, 500)
            .animate({"left": "+=300", "top": "+=100"}, 500);

        });

        $("p.fading").css("opacity","0.3");
        $("p.fading").hover(function() {
            $(this).stop().animate({opacity: 1.0}, "slow");}, 
                function () {
                $(this).stop().animate({opacity: 0.3}, "slow");
            });

        $("#rotateRight").click(function() {
            $("#cannonball").rotate(10);
        });

    }); //end jquery document.ready scripts

function initialize () {
    document.getElementById( box ).style.top = 250;
}
</script>

<style type="text/css">
body {
    background-color: #ccc;
}

.box {
    background-color: #000;
    width:100px;
    height:100px;
    margin-left:300px;
}

.divMove {
    position:relative;
    top:350px;
    float:right;
    background-color: #ddd;
    width:100px;
    height:100px;
    margin-right:100px;
}   

#cannonball {
    position: relative;
}
</style>
</head>
<body onload="initialize();">
<p>Let s make this disappear and appear.</p>

<button id="hide">Hide</button>
<button id="show">Show</button>
<button id="move">Move</button>
<button id="rotateRight">Rotate+</button>

<div id="box" class="box">
</div>


<div class="divMove" id="grey">
</div>

<img src="http://dl.dropbox.com/u/18833130/Webprogrammering/test/cannonball.png" id="cannonball" border="1" />
<p class="fading">This is a paragraph that fades. Let s see how it looks.</p>
</body>
</html>

我为那长长的邮箱和大量的代码道歉, 但如果你想尝试的话, 你可以基本上只是复制纸, 我认为这样讨论会更容易!

Answer 1

我想我要做两个不同的大炮物体,即大炮“基地”和大炮桶。然后,当播放器按键时,我可以旋转大炮桶。不幸的是,在网络编程中,轮换似乎很难。

最容易(现在)的办法是使用CSS transform 属性 :

const angleInputElement = document.getElementById( angle );
const degrees = angleInputElement.value;
const barrelElement = document.getElementById( barrel ); // I don t see this in your sample though
barrelElement.style.transform = `rotate(${degrees}deg)`;

另外,如果我想同时动画几个对象, 你认为我应该改变同一个游戏圈函数中的所有对象吗?

对于这一应当行之有效的简单实施来说,这一简单实施应当行之有效。

友情链接