在HTML5画布上绘制形状

Question

I have a function that basically uses lines to draw a psuedo circle of a specific size and fills it in a colour.

However when I try to call my method, it does not draw and I found no errors on the debug console (I'm using chrome) and jsfiddle threw up no errors for me.

Here is the code:

function drawLineCircle (x, y, size, colour, scale, segments) {
    context.save();

    context.strokestyle = '#000000';
    context.fillStyle   = colour;
    context.lineWidth   = 3;

    context.beginPath();

    var anglePerSegment = Math.PI *2 / segments;

    for (var i = 0; i <= segments; i = i + 1){
        var angle  = anglePerSegment * i;
        var radius = size * scale;
        var a      = x + radius * cos (angle);
        var b      = y + radius * sin (angle);
        if (i == 0)
            context.moveTo (a, b);
        else
            context.lineTo (a, b);

    }

    context.stroke();
    context.fill();

    context.closePath();
    context.restore();
}

Any help would be greatly appreciated!

Answer 1

There are a couple of problems with your code:

1. You are not defining context
2. cos and sin are properties of Math

Here is a corrected example: http://jsfiddle.net/REw7j/1/

function drawLineCircle (x, y, size, colour, scale, segments) {
    var canvas = document.getElementById('example');
    var context = canvas.getContext('2d');
    context.save();

    context.strokestyle = '#000000';
    context.fillStyle   = colour;
    context.lineWidth   = 3;

    context.beginPath();

    var anglePerSegment = Math.PI *2 / segments;

    for (var i = 0; i <= segments; i = i + 1){
        var angle  = anglePerSegment * i;
        var radius = size * scale;
        var a      = x + radius * Math.cos (angle);
        var b      = y + radius * Math.sin (angle);
        if (i == 0)
            context.moveTo (a, b);
        else
            context.lineTo (a, b);

    }

    context.stroke();
    context.fill();

    context.closePath();
    context.restore();
}