canvas动画基础

 setInterval(

        function(){

            render( context );

            update();

        }

        ,

    );

window.requestAnimFrame = (function() {

    return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||

        function( /* function FrameRequestCallback */ callback, /* DOMElement Element */ element) {

            return window.setTimeout(callback,  / );

        };

})();

window.requestAnimFrame = (function() {

    return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||

        function( /* function FrameRequestCallback */ callback, /* DOMElement Element */ element) {

            return window.setTimeout(callback,  / );

        };

})();

function calLength2(x1, y1, x2, y2) {

    return Math.pow(x1 - x2, ) + Math.pow(y1 - y2, );

}

function randomColor() {

    var col = [, , ];

    col[] = Math.random() *  + ;

    col[] = col[].toFixed();

    col[] = Math.random() *  + ;

    col[] = col[].toFixed();

    col[] = Math.random() *  + ;

    col[] = col[].toFixed();

    var num = Math.floor(Math.random() * );

    col[num] = ;

    return "rgba(" + col[] + "," + col[] + "," + col[] + ",";

}

function lerpAngle(a, b, t) {

    var d = b - a;

    if (d > Math.PI) d = d -  * Math.PI;

    if (d < -Math.PI) d = d +  * Math.PI;

    return a + d * t;

}

function inOboundary(arrX, arrY, l, r, t, b) { //在l r t b范围内的检测

    return arrX > l && arrX < r && arrY > t && arrY < b;

}

function rgbColor(r, g, b) {

    r = Math.round(r * );

    g = Math.round(g * );

    b = Math.round(b * );

    return "rgba(" + r + "," + g + "," + b + ",1)";

}

function rgbNum(r, g, b) {

    r = Math.round(r * );

    g = Math.round(g * );

    b = Math.round(b * );

    return "rgba(" + r + "," + g + "," + b;

}

function rnd(m) {

    var n = m || ;

    return Math.random() * n;

}

function rateRandom(m, n) {

    var sum = ;

    for (var i = ; i < (n - m); i++) {

        sum += i;

    }

    var ran = Math.random() * sum;

    for (var i = ; i < (n - m); i++) {

        ran -= i;

        if (ran < ) {

            return i -  + m;

        }

    }

}

function distance(x1, y1, x2, y2, l) {

    var x = Math.abs(x1 - x2);

    var y = Math.abs(y1 - y2);

    if (x < l && y < l) {

        return true;

    }

    return false;

}

function AABBbox(object1, w1, h1, object2, w2, h2, overlap) {

    A1 = object1.x + overlap;

    B1 = object1.x + w1 - overlap;

    C1 = object1.y + overlap;

    D1 = object1.y + h1 - overlap;

    A2 = object2.x + overlap;

    B2 = object2.x + w2 - overlap;

    C2 = object2.y + overlap;

    D2 = object2.y + h2 - overlap;

    if (A1 > B2 || B1 < A2 || C1 > D2 || D1 < C2) return false;

    else return true;

}

function dis2(x, y, x0, y0) {

    var dx = x - x0;

    var dy = y - y0;

    return dx * dx + dy * dy;

}

function rndi2(m, n) {

    var a = Math.random() * (n - m) + m;

    return Math.floor(a);

}