canvas html5的问题无法关闭绘图

Question

I'm developing a website where you can insert data of person, each person is represented by a image (a circle), the images are in a html table(the rows are the years and the columns are the months), depends of birth date, they will be in one position or other position. Well the thing is that I have to link the images with canvas to make a figure, a close figure. And by now I only managed to join it with lines, I know that if you use the property ".fill()" the figure will be closed, but it doesn't work and I don't know why. What I'm doing wrong?

Here is my js code: (I call the function "person" from the event onClick() in a button of the html, every time you insert a person)

    function position(year, mon) //this function puts the images
    {
        $('#' + year + ' .' + mon).prepend('<img class="black_point" src="./images/circle.png"/>');    
    }
    function person () {
        var date;
        date=prompt('Birthday date','01/01/1935');
        var elem = date.split('/'); 
        var month= elem[1]; //we take the month
        var year=elem[2]; //we take the year
        var mon= num2mon(month);
        var rw=document.getElementById("table").rows.length;
        var cols = $("#table").find('tr')[0].cells.length;
        position(year,mon);
     draw();
    }


    function draw() { //this function draw the lines
        var table = document.getElementById("table");
        var images = table.getElementsByTagName("img");  
        var canvas = document.getElementById("myCanvas");
        var ctx = canvas.getContext("2d");
        var x,y;

        canvas.width  = table.offsetWidth;
        canvas.height = table.offsetHeight;

          function connect(image) { //this function link the images
            var tabBcr = table.getBoundingClientRect();
            var imgBcr = image.getBoundingClientRect();
            ctx.beginPath();
            ctx.moveTo(x, y);

            x = imgBcr.left + (imgBcr.width / 2) - tabBcr.left;
            y = imgBcr.top + (imgBcr.height / 2) - tabBcr.top;

            ctx.lineTo(x, y);
            ctx.stroke();

            //ctx.fill(); //that's no work :S
            //ctx.closePath();

          }
        for(var i=0; i<images.length; i++){ 
          connect( images[i]);
        }
    }

Thank you!

Answer 1

There are two kind of paths in canvas, the main path and then sub-paths.

For a close to work you need to only have max one sub-path. Every time moveTo() is used a new sub-path will be created so when a line is made like this:

moveTo(x1, y1);
lineTo(x2, y2);
moveTo(x2, y2);
lineTo(x3, y3);

You have two sub-paths that are not connected. What you want is to continue adding lines to the existing sub-paths like this:

moveTo(x1, y1);
lineTo(x2, y2);
lineTo(x3, y3);

Now it is possible to close the shape connecting x3->x1 and y3->y1.

Using ctx.beginPath() in this case makes it worst. It will clear all sub-paths added to the main path.

What you need to do is to globally (or at some higher level) create a new path using beginPath() (every time you need to redraw the content for example).

Then the first line needs to be set using moveTo() . Then every other lines using lineTo() .

Finally you can use closePath() and render it using stroke() or fill() (closePath() is not needed with fill, with stroke it must be called before stroke).

For example (untested, adopt as needed):

function draw() { //this function draw the lines
    var table = document.getElementById("table");
    var images = table.getElementsByTagName("img");  
    var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    var x,y;

    canvas.width  = table.offsetWidth;
    canvas.height = table.offsetHeight;

    function connect(image, index) { //this function link the images
        var tabBcr = table.getBoundingClientRect();
        var imgBcr = image.getBoundingClientRect();

        x = imgBcr.left + (imgBcr.width / 2) - tabBcr.left;
        y = imgBcr.top + (imgBcr.height / 2) - tabBcr.top;

        index === 0 ? ctx.moveTo(x, y) : ctx.lineTo(x, y);
    }

    // new path here
    ctx.beginPath();

    for(var i=0; i<images.length; i++){ 
      connect( images[i], i);  // provide index so we can sep. move/line
    }

    // then at the end:
    ctx.fill();
}