//描点，参数有点的大小，颜色，点的坐标和标签; 很明显opts参数是一个对象
function drawPoint(opts){
    document.write("<span id=\'"+opts.point[0]+""+opts.point[1]+"\' style=\'display: inline-block; width: "+opts.pw+"px; height: "+opts.ph+"px; background-color: "+opts.color+"; position: absolute "+opts.point[0]+"px; top: "+opts.point[1]+"px;\'>"+(opts.point[2]?("<div style=\'position: relative;\'><span style=\'position: absolute; left: 5px; bottom: 1px; text-align: left; width: 100px;\'>"+opts.point[2]+"</span></div>"):"")+"</span>");
}

//画线
//pstart 起点
//pend 终点
//opts 参数
function drawLine(pstart, pend, opts){
    var ph = 1;
    var pw = 1;
    var color = "DarkRed";
    if(opts){
        color = opts.color ? opts.color: color;
    }
    var slope; //斜率
    var noSlope = false; //是否有斜率
    var hdist = pend[0] - pstart[0];
    var vdist = pend[1] - pstart[1];
    if(hdist != 0){
        slope =  Math.abs(vdist/hdist);  //计算斜率
    }else{
        noSlope = true; //当hdist=0时，直线没有斜率
    }
    var gapp = pw > ph ? ph : pw; //默认相邻点（左上角的像素点）间的距离
    
    var diagonal = Math.sqrt(Math.pow(hdist,2) + Math.pow(vdist,2)); //斜边长度
    var pn = parseInt(diagonal/gapp); //计算两点之间的点的数量
    if(pn < 3){pn=pn*3+1}; //如果点的数量小于3，则加大点数；为什么+1呢，是保证pn=0时至少有一个点
    var vgap = Math.abs(vdist)/pn; //相邻两点间的垂直距离
    var hgap = Math.abs(hdist)/pn; //相邻两点间的水平距离
    for(var i = 0; i< pn ; i++){
        //描点
        //hgap 相邻两点间的水平距离
        //vgap 相邻两点间的垂直距离
        //hgap*i*(pend[0]<pstart[0]?-1:1)*(noSlope?0:1) 相对于起点的水平偏移
        //vgap*i*(pend[1]<pstart[1]?-1:1) 相对于起点的垂直偏移
        //(pend[0]<pstart[0]?-1:1) 水平偏移方向
        //(pend[1]<pstart[1]?-1:1) 垂直偏移方向
        //(noSlope?0:1) 直线没有斜率时，水平偏移为0
        drawPoint({
            pw: pw,
            ph: ph,
            color: color,
            point: [(hgap*i*(pend[0]<pstart[0]?-1:1)*(noSlope?0:1)+pstart[0]),(vgap*i*(pend[1]<pstart[1]?-1:1)+pstart[1])]
        });
    }
}

//折线形
//ps 点的一维数组
function drawPolyline(ps){
    if(ps){
        //画线
        for(var i = 0; i<ps.length-1; i++){
            drawLine(ps[i], ps[i+1]);
        }
        //描拐点
        for(var i = 0; i<ps.length; i++){
            drawPoint({
                pw: 3,
                ph: 3,
                color: \'RED\',
                point: ps[i]
            });
        }
        
    }
}

//多边形
//ps 点的一维数组
function drawPolygon(ps){
    if(ps){
        //画线
        for(var i = 0; i<ps.length-1; i++){
            drawLine(ps[i], ps[i+1]);
        }
        //使闭合
        if(ps.length > 2){
            drawLine(ps[ps.length-1], ps[0])
        }
        //描拐点
        for(var i = 0; i<ps.length; i++){
            drawPoint({
                pw: 3,
                ph: 3,
                color: \'RED\',
                point: ps[i]
            });
        }
    }
}

//画矩形
//leftTop 左上角的点的位置
//width 宽
//high 高
function drawRectangle(leftTop, width, high){
    drawPolygon([
        leftTop,
        [leftTop[0], leftTop[1]+high],
        [leftTop[0]+width, leftTop[1]+high],
        [leftTop[0]+width, leftTop[1]]
    ]);
    //填充
    //document.write("<span style=\'height: "+(high-1)+"px; width: "+(width-1)+"px; background-color: "+"Green"+"; position: absolute; left:"+(leftTop[0]+1)+"px; top: "+(leftTop[1]+1)+"\'></span>");
}