Add d3.pathRound. (#12)

* pathFixed

* expose Path; template literal

* minimize diff

* minimize diff

* Path(digits); pathFixed(digits = 3)

* Update README

* simpler iteration

* pathRound, not pathFixed

* shorter

Co-authored-by: Philippe Rivière <fil@rezo.net>

Author: mbostock

README.md

@@ -21,12 +21,12 @@ Now code you write once can be used with both Canvas (for performance) and SVG (
 
 ## Installing
 
-If you use npm, `npm install d3-path`. You can also download the [latest release on GitHub](https://github.com/d3/d3-path/releases/latest). In modern browsers, you can import d3-path from Skypack:
+If you use npm, `npm install d3-path`. You can also download the [latest release on GitHub](https://github.com/d3/d3-path/releases/latest). In modern browsers, you can import d3-path from jsDelivr:
 
 ```html
 <script type="module">
 
-import {path} from "https://cdn.skypack.dev/d3-path@3";
+import {path} from "https://cdn.jsdelivr.net/npm/d3-path@3/+esm";
 
 const p = path();
 p.moveTo(1, 2);
@@ -88,3 +88,7 @@ Creates a new subpath containing just the four points ⟨*x*, *y*⟩, ⟨*x* + *
 <a name="path_toString" href="#path_toString">#</a> <i>path</i>.<b>toString</b>()
 
 Returns the string representation of this *path* according to SVG’s [path data specification](http://www.w3.org/TR/SVG/paths.html#PathData).
+
+<a name="pathRound" href="#pathRound">#</a> d3.<b>pathRound</b>(*digits* = 3) · [Source](https://github.com/d3/d3-path/blob/master/src/path.js), [Examples](https://observablehq.com/@d3/d3-path)
+
+Like [d3.path](#path), except limits the digits after the decimal to the specified number of *digits*.

src/index.js

@@ -1 +1 @@
-export {default as path} from "./path.js";
+export {Path, path, pathRound} from "./path.js";

src/path.js

@@ -3,52 +3,68 @@ const pi = Math.PI,
     epsilon = 1e-6,
     tauEpsilon = tau - epsilon;
 
-function Path() {
-  this._x0 = this._y0 = // start of current subpath
-  this._x1 = this._y1 = null; // end of current subpath
-  this._ = "";
+function append(strings) {
+  this._ += strings[0];
+  for (let i = 1, n = strings.length; i < n; ++i) {
+    this._ += arguments[i] + strings[i];
+  }
 }
 
-function path() {
-  return new Path;
+function appendRound(digits) {
+  let d = Math.floor(digits);
+  if (!(d >= 0)) throw new Error(`invalid digits: ${digits}`);
+  if (d > 15) return append;
+  const k = 10 ** d;
+  return function(strings) {
+    this._ += strings[0];
+    for (let i = 1, n = strings.length; i < n; ++i) {
+      this._ += Math.round(arguments[i] * k) / k + strings[i];
+    }
+  };
 }
 
-Path.prototype = path.prototype = {
-  constructor: Path,
-  moveTo: function(x, y) {
-    this._ += "M" + (this._x0 = this._x1 = +x) + "," + (this._y0 = this._y1 = +y);
-  },
-  closePath: function() {
+export class Path {
+  constructor(digits) {
+    this._x0 = this._y0 = // start of current subpath
+    this._x1 = this._y1 = null; // end of current subpath
+    this._ = "";
+    this._append = digits == null ? append : appendRound(digits);
+  }
+  moveTo(x, y) {
+    this._append`M${this._x0 = this._x1 = +x},${this._y0 = this._y1 = +y}`;
+  }
+  closePath() {
     if (this._x1 !== null) {
       this._x1 = this._x0, this._y1 = this._y0;
-      this._ += "Z";
+      this._append`Z`;
     }
-  },
-  lineTo: function(x, y) {
-    this._ += "L" + (this._x1 = +x) + "," + (this._y1 = +y);
-  },
-  quadraticCurveTo: function(x1, y1, x, y) {
-    this._ += "Q" + (+x1) + "," + (+y1) + "," + (this._x1 = +x) + "," + (this._y1 = +y);
-  },
-  bezierCurveTo: function(x1, y1, x2, y2, x, y) {
-    this._ += "C" + (+x1) + "," + (+y1) + "," + (+x2) + "," + (+y2) + "," + (this._x1 = +x) + "," + (this._y1 = +y);
-  },
-  arcTo: function(x1, y1, x2, y2, r) {
+  }
+  lineTo(x, y) {
+    this._append`L${this._x1 = +x},${this._y1 = +y}`;
+  }
+  quadraticCurveTo(x1, y1, x, y) {
+    this._append`Q${+x1},${+y1},${this._x1 = +x},${this._y1 = +y}`;
+  }
+  bezierCurveTo(x1, y1, x2, y2, x, y) {
+    this._append`C${+x1},${+y1},${+x2},${+y2},${this._x1 = +x},${this._y1 = +y}`;
+  }
+  arcTo(x1, y1, x2, y2, r) {
     x1 = +x1, y1 = +y1, x2 = +x2, y2 = +y2, r = +r;
-    var x0 = this._x1,
+
+    // Is the radius negative? Error.
+    if (r < 0) throw new Error(`negative radius: ${r}`);
+
+    let x0 = this._x1,
         y0 = this._y1,
         x21 = x2 - x1,
         y21 = y2 - y1,
         x01 = x0 - x1,
         y01 = y0 - y1,
         l01_2 = x01 * x01 + y01 * y01;
 
-    // Is the radius negative? Error.
-    if (r < 0) throw new Error("negative radius: " + r);
-
     // Is this path empty? Move to (x1,y1).
     if (this._x1 === null) {
-      this._ += "M" + (this._x1 = x1) + "," + (this._y1 = y1);
+      this._append`M${this._x1 = x1},${this._y1 = y1}`;
     }
 
     // Or, is (x1,y1) coincident with (x0,y0)? Do nothing.
@@ -58,12 +74,12 @@ Path.prototype = path.prototype = {
     // Equivalently, is (x1,y1) coincident with (x2,y2)?
     // Or, is the radius zero? Line to (x1,y1).
     else if (!(Math.abs(y01 * x21 - y21 * x01) > epsilon) || !r) {
-      this._ += "L" + (this._x1 = x1) + "," + (this._y1 = y1);
+      this._append`L${this._x1 = x1},${this._y1 = y1}`;
     }
 
     // Otherwise, draw an arc!
     else {
-      var x20 = x2 - x0,
+      let x20 = x2 - x0,
           y20 = y2 - y0,
           l21_2 = x21 * x21 + y21 * y21,
           l20_2 = x20 * x20 + y20 * y20,
@@ -75,32 +91,33 @@ Path.prototype = path.prototype = {
 
       // If the start tangent is not coincident with (x0,y0), line to.
       if (Math.abs(t01 - 1) > epsilon) {
-        this._ += "L" + (x1 + t01 * x01) + "," + (y1 + t01 * y01);
+        this._append`L${x1 + t01 * x01},${y1 + t01 * y01}`;
       }
 
-      this._ += "A" + r + "," + r + ",0,0," + (+(y01 * x20 > x01 * y20)) + "," + (this._x1 = x1 + t21 * x21) + "," + (this._y1 = y1 + t21 * y21);
+      this._append`A${r},${r},0,0,${+(y01 * x20 > x01 * y20)},${this._x1 = x1 + t21 * x21},${this._y1 = y1 + t21 * y21}`;
     }
-  },
-  arc: function(x, y, r, a0, a1, ccw) {
+  }
+  arc(x, y, r, a0, a1, ccw) {
     x = +x, y = +y, r = +r, ccw = !!ccw;
-    var dx = r * Math.cos(a0),
+
+    // Is the radius negative? Error.
+    if (r < 0) throw new Error(`negative radius: ${r}`);
+
+    let dx = r * Math.cos(a0),
         dy = r * Math.sin(a0),
         x0 = x + dx,
         y0 = y + dy,
         cw = 1 ^ ccw,
         da = ccw ? a0 - a1 : a1 - a0;
 
-    // Is the radius negative? Error.
-    if (r < 0) throw new Error("negative radius: " + r);
-
     // Is this path empty? Move to (x0,y0).
     if (this._x1 === null) {
-      this._ += "M" + x0 + "," + y0;
+      this._append`M${x0},${y0}`;
     }
 
     // Or, is (x0,y0) not coincident with the previous point? Line to (x0,y0).
     else if (Math.abs(this._x1 - x0) > epsilon || Math.abs(this._y1 - y0) > epsilon) {
-      this._ += "L" + x0 + "," + y0;
+      this._append`L${x0},${y0}`;
     }
 
     // Is this arc empty? We’re done.
@@ -111,20 +128,29 @@ Path.prototype = path.prototype = {
 
     // Is this a complete circle? Draw two arcs to complete the circle.
     if (da > tauEpsilon) {
-      this._ += "A" + r + "," + r + ",0,1," + cw + "," + (x - dx) + "," + (y - dy) + "A" + r + "," + r + ",0,1," + cw + "," + (this._x1 = x0) + "," + (this._y1 = y0);
+      this._append`A${r},${r},0,1,${cw},${x - dx},${y - dy}A${r},${r},0,1,${cw},${this._x1 = x0},${this._y1 = y0}`;
     }
 
     // Is this arc non-empty? Draw an arc!
     else if (da > epsilon) {
-      this._ += "A" + r + "," + r + ",0," + (+(da >= pi)) + "," + cw + "," + (this._x1 = x + r * Math.cos(a1)) + "," + (this._y1 = y + r * Math.sin(a1));
+      this._append`A${r},${r},0,${+(da >= pi)},${cw},${this._x1 = x + r * Math.cos(a1)},${this._y1 = y + r * Math.sin(a1)}`;
     }
-  },
-  rect: function(x, y, w, h) {
-    this._ += "M" + (this._x0 = this._x1 = +x) + "," + (this._y0 = this._y1 = +y) + "h" + (+w) + "v" + (+h) + "h" + (-w) + "Z";
-  },
-  toString: function() {
+  }
+  rect(x, y, w, h) {
+    this._append`M${this._x0 = this._x1 = +x},${this._y0 = this._y1 = +y}h${w = +w}v${+h}h${-w}Z`;
+  }
+  toString() {
     return this._;
   }
-};
+}
 
-export default path;
+export function path() {
+  return new Path;
+}
+
+// Allow instanceof d3.path
+path.prototype = Path.prototype;
+
+export function pathRound(digits = 3) {
+  return new Path(+digits);
+}

test/pathRound-test.js

@@ -0,0 +1,83 @@
+import assert from "assert";
+import {path, pathRound} from "../src/index.js";
+
+it("pathRound() defaults to three digits of precision", () => {
+  const p = pathRound();
+  p.moveTo(Math.PI, Math.E);
+  assert.strictEqual(p + "", "M3.142,2.718");
+});
+
+it("pathRound(null) is equivalent to pathRound(0)", () => {
+  const p = pathRound(null);
+  p.moveTo(Math.PI, Math.E);
+  assert.strictEqual(p + "", "M3,3");
+});
+
+it("pathRound(digits) validates the specified digits", () => {
+  assert.throws(() => pathRound(NaN), /invalid digits/);
+  assert.throws(() => pathRound(-1), /invalid digits/);
+});
+
+it("pathRound(digits) ignores digits if greater than 15", () => {
+  const p = pathRound(40);
+  p.moveTo(Math.PI, Math.E);
+  assert.strictEqual(p + "", "M3.141592653589793,2.718281828459045");
+});
+
+it("pathRound.moveTo(x, y) limits the precision", () => {
+  const p = pathRound(1);
+  p.moveTo(123.456, 789.012);
+  assert.strictEqual(p + "", "M123.5,789");
+});
+
+it("pathRound.lineTo(x, y) limits the precision", () => {
+  const p = pathRound(1);
+  p.moveTo(0, 0);
+  p.lineTo(123.456, 789.012);
+  assert.strictEqual(p + "", "M0,0L123.5,789");
+});
+
+it("pathRound.arc(x, y, r, a0, a1, ccw) limits the precision", () => {
+  const p0 = path(), p = pathRound(1);
+  p0.arc(10.0001, 10.0001, 123.456, 0, Math.PI+0.0001);
+  p.arc(10.0001, 10.0001, 123.456, 0, Math.PI+0.0001);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+  p0.arc(10.0001, 10.0001, 123.456, 0, Math.PI-0.0001);
+  p.arc(10.0001, 10.0001, 123.456, 0, Math.PI-0.0001);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+  p0.arc(10.0001, 10.0001, 123.456, 0, Math.PI / 2, true);
+  p.arc(10.0001, 10.0001, 123.456, 0, Math.PI / 2, true);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+});
+
+it("pathRound.arcTo(x1, y1, x2, y2, r) limits the precision", () => {
+  const p0 = path(), p = pathRound(1);
+  p0.arcTo(10.0001, 10.0001, 123.456, 456.789, 12345.6789);
+  p.arcTo(10.0001, 10.0001, 123.456, 456.789, 12345.6789);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+});
+
+it("pathRound.quadraticCurveTo(x1, y1, x, y) limits the precision", () => {
+  const p0 = path(), p = pathRound(1);
+  p0.quadraticCurveTo(10.0001, 10.0001, 123.456, 456.789);
+  p.quadraticCurveTo(10.0001, 10.0001, 123.456, 456.789);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+});
+
+it("pathRound.bezierCurveTo(x1, y1, x2, y2, x, y) limits the precision", () => {
+  const p0 = path(), p = pathRound(1);
+  p0.bezierCurveTo(10.0001, 10.0001, 123.456, 456.789, 0.007, 0.006);
+  p.bezierCurveTo(10.0001, 10.0001, 123.456, 456.789, 0.007, 0.006);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+});
+
+it("pathRound.rect(x, y, w, h) limits the precision", () => {
+  const p0 = path(), p = pathRound(1);
+  p0.rect(10.0001, 10.0001, 123.456, 456.789);
+  p.rect(10.0001, 10.0001, 123.456, 456.789);
+  assert.strictEqual(p + "", precision(p0 + "", 1));
+});
+
+function precision(str, precision) {
+  return str.replace(/\d+\.\d+/g, s => +parseFloat(s).toFixed(precision));
+}