HTML5重力感应小球冲撞动画实现教程

今天我们来分享一款很酷的HTML5重力感应动画教程，这款动画可以让你甩动页面中的小球，小球的大小都不同，并且鼠标点击空白区域时又可以生成一定数量的小球。当我们甩动小球时，各个小球之间就会发生互相碰撞的效果，并且在运动过程中模拟了重力感应的物理效果。你可以在DEMO演示中来尝试一下。

你也可以在这里查看在线演示

接下来我们来分析一下这款超酷的HTML5重力动画实现的思路及源码，主要由HTML代码和Javascript代码组成。

HTML代码：

<div id="canvas"></div>

还是很简单，HTML仅仅是列出了一个canvas容器，今后我们将在这里生成一些列canvas元素，这些小球就在canvas中运动。

另外由于该动画利用了box2d的js脚本库，所以在页面上你也需要引用它：

<script src="box2d.js"></script>

接下来是Javascript代码，在canvas上动态创建大小和样式不一的小球，并发生碰撞效果。

Javascript代码：

var canvas;



var delta = [ 0, 0 ];

var stage = [ window.screenX, window.screenY, window.innerWidth, window.innerHeight ];

getBrowserDimensions();



var themes = [ [ "#10222B", "#95AB63", "#BDD684", "#E2F0D6", "#F6FFE0" ],

        [ "#362C2A", "#732420", "#BF734C", "#FAD9A0", "#736859" ],

        [ "#0D1114", "#102C2E", "#695F4C", "#EBBC5E", "#FFFBB8" ],

        [ "#2E2F38", "#FFD63E", "#FFB54B", "#E88638", "#8A221C" ],

        [ "#121212", "#E6F2DA", "#C9F24B", "#4D7B85", "#23383D" ],

        [ "#343F40", "#736751", "#F2D7B6", "#BFAC95", "#8C3F3F" ],

        [ "#000000", "#2D2B2A", "#561812", "#B81111", "#FFFFFF" ],

        [ "#333B3A", "#B4BD51", "#543B38", "#61594D", "#B8925A" ] ];

var theme;



var worldAABB, world, iterations = 1, timeStep = 1 / 15;



var walls = [];

var wall_thickness = 200;

var wallsSetted = false;



var bodies, elements, text;



var createMode = false;

var destroyMode = false;



var isMouseDown = false;

var mouseJoint;

var mouse = { x: 0, y: 0 };

var gravity = { x: 0, y: 1 };



var PI2 = Math.PI * 2;



var timeOfLastTouch = 0;



init();

play();



function init() {



    canvas = document.getElementById( 'canvas' );



    document.onmousedown = onDocumentMouseDown;

    document.onmouseup = onDocumentMouseUp;

    document.onmousemove = onDocumentMouseMove;

    document.ondblclick = onDocumentDoubleClick;



    document.addEventListener( 'touchstart', onDocumentTouchStart, false );

    document.addEventListener( 'touchmove', onDocumentTouchMove, false );

    document.addEventListener( 'touchend', onDocumentTouchEnd, false );



    window.addEventListener( 'deviceorientation', onWindowDeviceOrientation, false );



    // init box2d



    worldAABB = new b2AABB();

    worldAABB.minVertex.Set( -200, -200 );

    worldAABB.maxVertex.Set( window.innerWidth + 200, window.innerHeight + 200 );



    world = new b2World( worldAABB, new b2Vec2( 0, 0 ), true );



    setWalls();

    reset();

}





function play() {



    setInterval( loop, 1000 / 40 );

}



function reset() {



    var i;



    if ( bodies ) {



        for ( i = 0; i < bodies.length; i++ ) {



            var body = bodies[ i ]

            canvas.removeChild( body.GetUserData().element );

            world.DestroyBody( body );

            body = null;

        }

    }



    // color theme

    theme = themes[ Math.random() * themes.length >> 0 ];

    document.body.style[ 'backgroundColor' ] = theme[ 0 ];



    bodies = [];

    elements = [];



    createInstructions();



    for( i = 0; i < 10; i++ ) {



        createBall();



    }



}



//



function onDocumentMouseDown() {



    isMouseDown = true;

    return false;

}



function onDocumentMouseUp() {



    isMouseDown = false;

    return false;

}



function onDocumentMouseMove( event ) {



    mouse.x = event.clientX;

    mouse.y = event.clientY;

}



function onDocumentDoubleClick() {



    reset();

}



function onDocumentTouchStart( event ) {



    if( event.touches.length == 1 ) {



        event.preventDefault();



        // Faking double click for touch devices



        var now = new Date().getTime();



        if ( now - timeOfLastTouch  < 250 ) {



            reset();

            return;

        }



        timeOfLastTouch = now;



        mouse.x = event.touches[ 0 ].pageX;

        mouse.y = event.touches[ 0 ].pageY;

        isMouseDown = true;

    }

}



function onDocumentTouchMove( event ) {



    if ( event.touches.length == 1 ) {



        event.preventDefault();



        mouse.x = event.touches[ 0 ].pageX;

        mouse.y = event.touches[ 0 ].pageY;



    }



}



function onDocumentTouchEnd( event ) {



    if ( event.touches.length == 0 ) {



        event.preventDefault();

        isMouseDown = false;



    }



}



function onWindowDeviceOrientation( event ) {



    if ( event.beta ) {



        gravity.x = Math.sin( event.gamma * Math.PI / 180 );

        gravity.y = Math.sin( ( Math.PI / 4 ) + event.beta * Math.PI / 180 );



    }



}



//



function createInstructions() {



    var size = 250;



    var element = document.createElement( 'div' );

    element.width = size;

    element.height = size;    

    element.style.position = 'absolute';

    element.style.left = -200 + 'px';

    element.style.top = -200 + 'px';

    element.style.cursor = "default";



    canvas.appendChild(element);

    elements.push( element );



    var circle = document.createElement( 'canvas' );

    circle.width = size;

    circle.height = size;



    var graphics = circle.getContext( '2d' );



    graphics.fillStyle = theme[ 3 ];

    graphics.beginPath();

    graphics.arc( size * .5, size * .5, size * .5, 0, PI2, true );

    graphics.closePath();

    graphics.fill();



    element.appendChild( circle );



    text = document.createElement( 'div' );

    text.onSelectStart = null;

    text.innerHTML = '<span style="color:' + theme[0] + ';font-size:40px;">Hello!</span><br /><br /><span style="font-size:15px;"><strong>This is how it works:</strong><br /><br />1. Drag a ball.<br />2.&nbsp;Click&nbsp;on&nbsp;the&nbsp;background.<br />3. Shake your browser.<br />4. Double click.<br />5. Play!</span>';

    text.style.color = theme[1];

    text.style.position = 'absolute';

    text.style.left = '0px';

    text.style.top = '0px';

    text.style.fontFamily = 'Georgia';

    text.style.textAlign = 'center';

    element.appendChild(text);



    text.style.left = ((250 - text.clientWidth) / 2) +'px';

    text.style.top = ((250 - text.clientHeight) / 2) +'px';    



    var b2body = new b2BodyDef();



    var circle = new b2CircleDef();

    circle.radius = size / 2;

    circle.density = 1;

    circle.friction = 0.3;

    circle.restitution = 0.3;

    b2body.AddShape(circle);

    b2body.userData = {element: element};



    b2body.position.Set( Math.random() * stage[2], Math.random() * -200 );

    b2body.linearVelocity.Set( Math.random() * 400 - 200, Math.random() * 400 - 200 );

    bodies.push( world.CreateBody(b2body) );    

}



function createBall( x, y ) {



    var x = x || Math.random() * stage[2];

    var y = y || Math.random() * -200;



    var size = (Math.random() * 100 >> 0) + 20;



    var element = document.createElement("canvas");

    element.width = size;

    element.height = size;

    element.style.position = 'absolute';

    element.style.left = -200 + 'px';

    element.style.top = -200 + 'px';

    element.style.WebkitTransform = 'translateZ(0)';

    element.style.MozTransform = 'translateZ(0)';

    element.style.OTransform = 'translateZ(0)';

    element.style.msTransform = 'translateZ(0)';

    element.style.transform = 'translateZ(0)';



    var graphics = element.getContext("2d");



    var num_circles = Math.random() * 10 >> 0;



    for (var i = size; i > 0; i-= (size/num_circles)) {



        graphics.fillStyle = theme[ (Math.random() * 4 >> 0) + 1];

        graphics.beginPath();

        graphics.arc(size * .5, size * .5, i * .5, 0, PI2, true); 

        graphics.closePath();

        graphics.fill();

    }



    canvas.appendChild(element);



    elements.push( element );



    var b2body = new b2BodyDef();



    var circle = new b2CircleDef();

    circle.radius = size >> 1;

    circle.density = 1;

    circle.friction = 0.3;

    circle.restitution = 0.3;

    b2body.AddShape(circle);

    b2body.userData = {element: element};



    b2body.position.Set( x, y );

    b2body.linearVelocity.Set( Math.random() * 400 - 200, Math.random() * 400 - 200 );

    bodies.push( world.CreateBody(b2body) );

}



//



function loop() {



    if (getBrowserDimensions()) {



        setWalls();



    }



    delta[0] += (0 - delta[0]) * .5;

    delta[1] += (0 - delta[1]) * .5;



    world.m_gravity.x = gravity.x * 350 + delta[0];

    world.m_gravity.y = gravity.y * 350 + delta[1];



    mouseDrag();

    world.Step(timeStep, iterations);



    for (i = 0; i < bodies.length; i++) {



        var body = bodies[i];

        var element = elements[i];



        element.style.left = (body.m_position0.x - (element.width >> 1)) + 'px';

        element.style.top = (body.m_position0.y - (element.height >> 1)) + 'px';



        if (element.tagName == 'DIV') {



            var style = 'rotate(' + (body.m_rotation0 * 57.2957795) + 'deg) translateZ(0)';

            text.style.WebkitTransform = style;

            text.style.MozTransform = style;

            text.style.OTransform = style;

            text.style.msTransform = style;

            text.style.transform = style;



        }



    }



}





// .. BOX2D UTILS



function createBox(world, x, y, width, height, fixed) {



    if (typeof(fixed) == 'undefined') {



        fixed = true;



    }



    var boxSd = new b2BoxDef();



    if (!fixed) {



        boxSd.density = 1.0;



    }



    boxSd.extents.Set(width, height);



    var boxBd = new b2BodyDef();

    boxBd.AddShape(boxSd);

    boxBd.position.Set(x,y);



    return world.CreateBody(boxBd);



}



function mouseDrag()

{

    // mouse press

    if (createMode) {



        createBall( mouse.x, mouse.y );



    } else if (isMouseDown && !mouseJoint) {



        var body = getBodyAtMouse();



        if (body) {



            var md = new b2MouseJointDef();

            md.body1 = world.m_groundBody;

            md.body2 = body;

            md.target.Set(mouse.x, mouse.y);

            md.maxForce = 30000 * body.m_mass;

            // md.timeStep = timeStep;

            mouseJoint = world.CreateJoint(md);

            body.WakeUp();



        } else {



            createMode = true;



        }



    }



    // mouse release

    if (!isMouseDown) {



        createMode = false;

        destroyMode = false;



        if (mouseJoint) {



            world.DestroyJoint(mouseJoint);

            mouseJoint = null;



        }



    }



    // mouse move

    if (mouseJoint) {



        var p2 = new b2Vec2(mouse.x, mouse.y);

        mouseJoint.SetTarget(p2);

    }

}



function getBodyAtMouse() {



    // Make a small box.

    var mousePVec = new b2Vec2();

    mousePVec.Set(mouse.x, mouse.y);



    var aabb = new b2AABB();

    aabb.minVertex.Set(mouse.x - 1, mouse.y - 1);

    aabb.maxVertex.Set(mouse.x + 1, mouse.y + 1);



    // Query the world for overlapping shapes.

    var k_maxCount = 10;

    var shapes = new Array();

    var count = world.Query(aabb, shapes, k_maxCount);

    var body = null;



    for (var i = 0; i < count; ++i) {



        if (shapes[i].m_body.IsStatic() == false) {



            if ( shapes[i].TestPoint(mousePVec) ) {



                body = shapes[i].m_body;

                break;



            }



        }



    }



    return body;



}



function setWalls() {



    if (wallsSetted) {



        world.DestroyBody(walls[0]);

        world.DestroyBody(walls[1]);

        world.DestroyBody(walls[2]);

        world.DestroyBody(walls[3]);



        walls[0] = null; 

        walls[1] = null;

        walls[2] = null;

        walls[3] = null;

    }



    walls[0] = createBox(world, stage[2] / 2, - wall_thickness, stage[2], wall_thickness);

    walls[1] = createBox(world, stage[2] / 2, stage[3] + wall_thickness, stage[2], wall_thickness);

    walls[2] = createBox(world, - wall_thickness, stage[3] / 2, wall_thickness, stage[3]);

    walls[3] = createBox(world, stage[2] + wall_thickness, stage[3] / 2, wall_thickness, stage[3]);    



    wallsSetted = true;



}



// BROWSER DIMENSIONS



function getBrowserDimensions() {



    var changed = false;



    if (stage[0] != window.screenX) {



        delta[0] = (window.screenX - stage[0]) * 50;

        stage[0] = window.screenX;

        changed = true;



    }



    if (stage[1] != window.screenY) {



        delta[1] = (window.screenY - stage[1]) * 50;

        stage[1] = window.screenY;

        changed = true;



    }



    if (stage[2] != window.innerWidth) {



        stage[2] = window.innerWidth;

        changed = true;



    }



    if (stage[3] != window.innerHeight) {



        stage[3] = window.innerHeight;

        changed = true;



    }



    return changed;



}

上面mouseDrag方法就实现了鼠标拖拽甩动小球的功能，这也是该动画最重要的方法。全部代码可以下载源码来研究。源码下载>>