How can I apply a clipPath in SVG with multiple paths and NOT clip out the area between the paths?

Question

I have an SVG clipPath made of multiple path elements, which I need to apply to a group of elements. I only want to clip out the area under the path stroke itself, not in between the paths. (example that doesn't do what I want follows)

var lineData = [ { "x": 1,   "y": 5},  { "x": 100,  "y": 400},
                  { "x": 300,  "y": 100}, { "x": 600,  "y": 600}, 
                  { "x": 700, "y": 50} ];
var lineData2 = [ { "x": 1,   "y": 500},  { "x": 100,  "y": 100},
                  { "x": 300,  "y": 700}, { "x": 600,  "y": 60},
                  { "x": 700,   "y": 700} ]; 


var lineFunction = d3.line()
    .x(function(d) { return d.x; })
    .y(function(d) { return d.y; })
    .curve(d3.curveBundle);

var svg = d3.select('body')
    .append('svg')
    .attr('id', 'svg')
    .attr('width', 660)
    .attr('height', 660)
    .style('outline', '1px solid red')
    .append('g')
    .attr('clip-path', 'url(#clippy)');

var polygon = svg.append('polygon')
    .attr('points', '230 10, 660 330, 230 650')
    .attr('fill', '#c99');

var circle = svg.append('circle')
    .attr('cx', 230)
    .attr('cy', 330)
    .attr('r', 200)
    .attr('fill', '#9c6')

var clippy = d3.select('#svg')
    .append('defs')
    .append('clipPath')
    .attr('id', 'clippy');

clippy.append("path")
    .attr("d", lineFunction(lineData))
    .attr("stroke", "blue")
    .attr("stroke-width", 18)
    .attr("fill", "none");

clippy.append("path")
    .attr("d", lineFunction(lineData2))
    .attr("stroke", "blue")
    .attr("stroke-width", 18)
    .attr("fill", "none");

Basically I want to accomplish something similar to what you get using letters, but instead using lines/paths.

var lineData = [ { "x": 1,   "y": 5},  { "x": 100,  "y": 400},
                  { "x": 300,  "y": 100}, { "x": 600,  "y": 600}, 
                  { "x": 700, "y": 50} ];
var lineData2 = [ { "x": 1,   "y": 500},  { "x": 100,  "y": 100},
                  { "x": 300,  "y": 700}, { "x": 600,  "y": 60},
                  { "x": 700,   "y": 700} ]; 


var lineFunction = d3.line()
    .x(function(d) { return d.x; })
    .y(function(d) { return d.y; })
    .curve(d3.curveBundle);

var svg = d3.select('body')
    .append('svg')
    .attr('id', 'svg')
    .attr('width', 660)
    .attr('height', 660)
    .style('outline', '1px solid red')
    .append('g')
    .attr('clip-path', 'url(#clippy)');

var polygon = svg.append('polygon')
    .attr('points', '230 10, 660 330, 230 650')
    .attr('fill', '#c99');

var circle = svg.append('circle')
    .attr('cx', 230)
    .attr('cy', 330)
    .attr('r', 200)
    .attr('fill', '#9c6')

var clippy = d3.select('#svg')
    .append('defs')
    .append('clipPath')
    .attr('id', 'clippy');

clippy.append('text')
    .attr('x', 120)
    .attr('y', 320)
    .attr('font-size', '4em')
    .attr('font-weight', 'bold')
    .attr('font-family', 'Georgia')
    .text('This is a clip');

clippy.append('text')
    .attr('x', 120)
    .attr('y', 420)
    .attr('font-size', '4em')
    .attr('font-weight', 'bold')
    .attr('font-family', 'Georgia')
    .text('Also a clip')

Please help!

EDIT: Here's a Codepen with both examples.

Answer 1

From my reading of the SVG spec, it's not possible to use only a <path>'s stroke as the clipping path:

The raw geometry of each child element exclusive of rendering properties such as ‘fill’, ‘stroke’, ‘stroke-width’ within a ‘clipPath’ conceptually defines a 1-bit mask (with the possible exception of anti-aliasing along the edge of the geometry) which represents the silhouette of the graphics associated with that element. Anything outside the outline of the object is masked out.

However, converting the <clipPath> to a <mask> element produces what I think is your desired effect. Here's a forked CodePen to demonstrate — the paths have have their strokes set to white, and the <text> elements were also given a fill of white to match the clip-path effect.