added perf example for sweep

There is a case when sweep line is still faster

README.md

@@ -92,6 +92,17 @@ Bush shortens. Sweep line comes last.
 Now Bush algorithm wins by huge margin. Bentley-Ottman comes second, and brute
 force comes the last.
 
+### Parallel Slanted lines
+
+[![slanted](https://i.imgur.com/vYAZzNvm.png)](https://anvaka.github.io/isect/?isAsync=false&p0=1000&p1=40&generator=parallelSlanted&algorithm=sweep&stepsPerFrame=1)
+
+* **Sweep: 1000 slanted, not intersect x 622 ops/sec ±1.23% (91 runs sampled)**
+* Brute: 1000 slanted, not intersect x 230 ops/sec ±2.37% (87 runs sampled)
+* Bush: 1000 slanted, not intersect x 243 ops/sec ±1.07% (87 runs sampled)
+
+In this example there too many lines, and none of them intersect. Furthermore, most of the
+rectangular bounding boxes do intersect, which gives more work for the `bush` algorithm
+
 # usage
 
 Install the module from npm:

demo/interactive/src/generators.js

@@ -20,6 +20,18 @@ export function random(count = 4, range = 100, seed) {
   return lines;
 }
 
+export function parallelSlanted(count) {
+  var lines = [];
+  for (var i = 0; i < count; ++i) {
+    var x = -i, y = i;
+    lines.push({
+      from: {x, y},
+      to: {x: i, y: i + i}
+    })
+  }
+  return lines;
+}
+
 export function sparse(size = 50) {
   var lines = [];
   var rows = size, columns = size;

perf/generators.js

@@ -14,7 +14,8 @@ module.exports = {
   grid: grid,
   complete: complete,
   drunkGrid: drunkGrid,
-  sparse: sparse
+  sparse: sparse,
+  parallelSlanted: parallelSlanted
 }
 
 function sparse(size, seed) {
@@ -37,6 +38,19 @@ function sparse(size, seed) {
   return lines;
 }
 
+function parallelSlanted(count) {
+  var lines = [];
+  for (var i = 0; i < count; ++i) {
+    var x = -i, y = i;
+    lines.push({
+      from: {x, y},
+      to: {x: i, y: i + i}
+    })
+  }
+  return lines;
+}
+
+
 function random(count = 4, range = 100, seed) {
   if (seed !== undefined) {
     prng = createRandom(seed);

perf/index.js

@@ -20,6 +20,10 @@ var sparseLines = g.sparse(50, seed);
 var bruteSparseLines = g.sparse(50, seed);
 var bushSparseLines = g.sparse(50, seed);
 
+var slanted = g.parallelSlanted(1000);
+var bruteSlanted = g.parallelSlanted(1000);
+var bushSlanted = g.parallelSlanted(1000);
+
 var aLines = lines.map(x => [[x.from.x, x.from.y], [x.to.x, x.to.y]]);
 var aRandomLines = randomLines.map(x => [[x.from.x, x.from.y], [x.to.x, x.to.y]]);
 
@@ -69,7 +73,18 @@ suite.add('Sweep: Circular lines 12x40', function() {
   var res = bush(bushSparseLines).run();
   if (res.length !== 358) throw new Error('Invalid number of intersections');
 })
-
+.add('Sweep: 1,000 slanted, not intersect', function() {
+  var res = sweep(slanted).run();
+  if (res.length !== 0) throw new Error('Invalid number of intersections');
+})
+.add('Brute: 1,000 slanted, not intersect', function() {
+  var res = brute(bruteSlanted).run();
+  if (res.length !== 0) throw new Error('Invalid number of intersections');
+})
+.add('Bush: 1,000 slanted, not intersect', function() {
+  var res = brute(bushSlanted).run();
+  if (res.length !== 0) throw new Error('Invalid number of intersections');
+})
 // .add('Alternative circular lines 12x40', function () {
 //   var res = alternativeImplementation(aRandomLines);
 //   if (res.length !== 1123) throw new Error('Invalid number of intersections');