js画图实例：正弦曲线

//画正弦曲线
//dot 原点
//amplitude    振幅 -- A
//initialPhase 初相 -- φ
//setover 偏距 -- k
//palstance 角速度 -- ω
//len 周期数
function drawSinusoid(dot, amplitude,initialPhase,palstance,setover, len, opts){
    var color = opts&&opts.color?opts.color:"DarkRed"; //曲线的颜色
    var max = len*2*Math.PI/w; //x的最大值
    //var x = -2*Math.PI/w/3;
    var x = 0; //x的初值
    var pre = [dot[0]+x, dot[1]+(amplitude*Math.sin(palstance*x+initialPhase)+setover)]; //y的初值
    for(;x < max;x+=5){ //每五个单位画一条线
        var cur = [dot[0]+x, dot[1]+(amplitude*Math.sin(palstance*x+initialPhase)+setover)];
        drawLine(pre, cur, {color: color}); // 画线
        pre = cur;
    }
    var d = Math.PI/(2*w);
    for(var x =0;x < max;x+=d){//描点
        var cur = [dot[0]+x, dot[1]+(amplitude*Math.sin(palstance*x+initialPhase)+setover)];
        drawPoint({
            pw:3,ph:3,color:'DarkRed',point: cur
        });
    }
    var pend = [dot[0]+max, dot[1]+(amplitude*Math.sin(palstance*max+initialPhase)+setover)];
    drawPoint({
        pw:3,ph:3,color:'DarkRed',point: pend
    });
    drawLine(pre, pend);
}