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);
}