d3.js: paintbrush with d3.svg.area problems

Question

I am trying to make a tool to draw an arbitrary figure like in this example - Line Drawing, but using path itself with fill - not stroke. Here is what i already done - https://jsfiddle.net/zeleniy/b14paam2/. Example already contains single arbitrary path figure, but you can draw by yourself using dragging.

As you can see a have two troubles:

1. Nib is sloped i do not know why. As consequence when draw diagonal line from top-right to bottom-left or vice versa path almost invisible.

2. In places where path intersect itself filling are absent.

How to fix this problems?

Answer 1

You can use line instead of area, it is more suitable for brush.

var path;

var area = d3.svg.line()
  .x(function(d) { return d[0]; })
  .y(function(d) { return d[1]; })
  .tension(0)
  .interpolate("basis");

var svg = d3.select("svg")
 .call(d3.behavior.drag()
  .on("dragstart", dragstarted)
    .on("drag", dragged)
    .on("dragend", dragended));

function dragstarted() {
  path = svg.append("path").datum([]).attr("class", "line")
     .attr({
         "fill": "none",
          "stroke": "lightblue",
          "stroke-width": 25 + "px",
          "stroke-linejoin": "round"
        });
}

function dragged() {
  path.datum().push(d3.mouse(this));
  path.attr("d", area);
}

function dragended() {
  path = null;
}

svg {
  border: 2px solid gray;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.3.13/d3.min.js"></script>
<h2>Paint with brush</h2>
<svg width="100%" height="300px"></svg>