initial creation of mirror plugin

packages/plugin-mirror/.babelrc

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+{
+  "presets": [
+    [
+      "@babel/preset-env",
+      {
+        "useBuiltIns": "entry"
+      }
+    ]
+  ]
+}

packages/plugin-mirror/CHANGELOG.md

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+# Change log for: @freesewing/plugin-mirror
+
+## Unreleased

packages/plugin-mirror/README.md

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+![FreeSewing](https://freesewing.org/banner.jpg)
+
+<p align='center'><a
+  href="https://www.npmjs.com/package/@freesewing/plugin-mirror"
+  title="@freesewing/plugin-mirror on NPM"
+  ><img src="https://img.shields.io/npm/v/@freesewing/plugin-mirror.svg"
+  alt="@freesewing/plugin-mirror on NPM"/>
+  </a><a
+  href="https://opensource.org/licenses/MIT"
+  title="License: MIT"
+  ><img src="https://img.shields.io/npm/l/@freesewing/plugin-mirror.svg?label=License"
+  alt="License: MIT"/>
+  </a><a
+  href="https://deepscan.io/dashboard#view=project&tid=2114&pid=2993&bid=23256"
+  title="Code quality on DeepScan"
+  ><img src="https://deepscan.io/api/teams/2114/projects/2993/branches/23256/badge/grade.svg"
+  alt="Code quality on DeepScan"/>
+  </a><a
+  href="https://github.com/freesewing/freesewing/issues?q=is%3Aissue+is%3Aopen+label%3Apkg%3Aplugin-mirror"
+  title="Open issues tagged pkg:plugin-mirror"
+  ><img src="https://img.shields.io/github/issues/freesewing/freesewing/pkg:plugin-mirror.svg?label=Issues"
+  alt="Open issues tagged pkg:plugin-mirror"/>
+  </a></p><p align='center'><a
+  href="https://twitter.com/freesewing_org"
+  title="Follow @freesewing_org on Twitter"
+  ><img src="https://img.shields.io/badge/%F3%A0%80%A0-Follow%20us-blue.svg?logo=twitter&logoColor=white&logoWidth=15"
+  alt="Follow @freesewing_org on Twitter"/>
+  </a><a
+  href="https://gitter.im/freesewing/chat"
+  title="Chat with us on Gitter"
+  ><img src="https://img.shields.io/badge/%F3%A0%80%A0-Chat%20with%20us-CA0547.svg?logo=gitter&logoColor=white&logoWidth=15"
+  alt="Chat with us on Gitter"/>
+  </a><a
+  href="https://freesewing.org/patrons/join"
+  title="Become a FreeSewing Patron"
+  ><img src="https://img.shields.io/badge/%F3%A0%80%A0-Support%20us-blueviolet.svg?logo=cash-app&logoColor=white&logoWidth=15"
+  alt="Become a FreeSewing Patron"/>
+  </a><a
+  href="https://instagram.com/freesewing_org"
+  title="Follow @freesewing_org on Twitter"
+  ><img src="https://img.shields.io/badge/%F3%A0%80%A0-Follow%20us-E4405F.svg?logo=instagram&logoColor=white&logoWidth=15"
+  alt="Follow @freesewing_org on Twitter"/>
+  </a></p>
+
+## What am I looking at? 🤔
+
+This repository is our _monorepo_ holding [all our NPM packages](https://www.npmjs.com/search?q=keywords:freesewing).  
+This folder holds **@freesewing/plugin-mirror**
+
+A FreeSewing plugin to mirror parts and points accross a line
+
+## About FreeSewing 💀
+
+Where the world of makers and developers collide, that's where you'll find FreeSewing.
+
+Our [core library](https://freesewing.dev/reference/api/) is a _batteries-included_ toolbox
+for parametric design of sewing patterns. It's a modular system (check our list
+of [plugins](https://freesewing.dev/reference/plugins/) and getting started is as simple as:
+
+```bash
+npm init freesewing-pattern
+```
+
+The [getting started](https://freesewing.dev/guides/getting-started/) section on [freesewing.dev](https://freesewing.dev/) is a good
+entrypoint to our documentation, but you'll find a lot more there, including
+our [API reference](https://freesewing.dev/reference/api/),
+as well as [our turorial](https://freesewing.dev/tutorials/pattern-design/),
+and [howtos](https://freesewing.dev/howtos/).
+
+If you're a maker, checkout [freesewing.org](https://freesewing/) where you can generate
+our sewing patterns adapted to your measurements.
+
+## Support FreeSewing: Become a patron 🥰
+
+FreeSewing is an open source project run by a community,
+and financially supported by our patrons.
+
+If you feel what we do is worthwhile, you too
+should [become a patron](https://freesewing.org/patrons/join).
+
+## Links 👩‍💻
+
+- 💻 Makers website: [freesewing.org](https://freesewing.org)
+- 💻 Developers website: [freesewing.dev](https://freesewing.dev)
+- 💬 Chat: [gitter.im/freesewing](https://gitter.im/freesewing/chat)
+- 🐦 Twitter: [@freesewing_org](https://twitter.com/freesewing_org)
+- 📷 Instagram: [@freesewing_org](https://instagram.com/freesewing_org)
+
+## License: MIT 🤓
+
+© [Joost De Cock](https://github.com/joostdecock).  
+See [the license file](https://github.com/freesewing/freesewing/blob/develop/LICENSE) for details.
+
+## Where to get help 🤯
+
+Our [chatroom on Gitter](https://gitter.im/freesewing/chat) is the best place to ask questions,
+share your feedback, or just hang out.
+
+If you want to report a problem, please [create an issue](https://github.com/freesewing/freesewing/issues/new).

packages/plugin-mirror/package.json

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+{
+  "name": "@freesewing/plugin-mirror",
+  "version": "2.6.0",
+  "description": "A FreeSewing plugin to mirror paths and points accross a line",
+  "author": "Joost De Cock <joost@decock.org> (https://github.com/joostdecock)",
+  "homepage": "https://freesewing.org/",
+  "repository": "github:freesewing/freesewing",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/freesewing/freesewing/issues"
+  },
+  "keywords": [
+    "freesewing",
+    "plugin",
+    "sewing pattern",
+    "sewing",
+    "design",
+    "parametric design",
+    "made to measure",
+    "diy",
+    "fashion"
+  ],
+  "main": "dist/index.js",
+  "module": "dist/index.mjs",
+  "scripts": {
+    "clean": "rimraf dist",
+    "build": "npm run clean && rollup -c",
+    "test": "echo \"plugin-mirrors: No tests configured. Perhaps you'd like to do this?\" && exit 0",
+    "pubtest": "npm publish --registry http://localhost:6662",
+    "pubforce": "npm publish",
+    "symlink": "mkdir -p ./node_modules/@freesewing && cd ./node_modules/@freesewing && ln -s -f ../../../* . && cd -",
+    "start": "rollup -c -w"
+  },
+  "peerDependencies": {
+    "@freesewing/core": "^2.6.0"
+  },
+  "dependencies": {},
+  "devDependencies": {},
+  "files": [
+    "dist/*",
+    "README.md",
+    "package.json"
+  ],
+  "publishConfig": {
+    "access": "public",
+    "tag": "latest"
+  },
+  "engines": {
+    "node": ">=8.0.0",
+    "npm": ">=5"
+  }
+}

packages/plugin-mirror/rollup.config.js

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+import babel from 'rollup-plugin-babel'
+import resolve from 'rollup-plugin-node-resolve'
+import commonjs from 'rollup-plugin-commonjs'
+import json from 'rollup-plugin-json'
+import minify from 'rollup-plugin-babel-minify'
+import peerDepsExternal from 'rollup-plugin-peer-deps-external'
+import { name, version, description, author, license, main, module } from './package.json'
+
+const output = [
+  {
+    file: main,
+    format: 'cjs',
+    sourcemap: true
+  }
+]
+if (typeof module !== 'undefined')
+  output.push({
+    file: module,
+    format: 'es',
+    sourcemap: true
+  })
+
+export default {
+  input: 'src/index.js',
+  output,
+  plugins: [
+    peerDepsExternal(),
+    resolve({ modulesOnly: true }),
+    commonjs(),
+    json(),
+    babel({
+      exclude: 'node_modules/**',
+      plugins: ['@babel/plugin-proposal-object-rest-spread']
+    }),
+    minify({
+      comments: false,
+      sourceMap: true,
+      banner: `/**\n * ${name} | v${version}\n * ${description}\n * (c) ${new Date().getFullYear()} ${author}\n * @license ${license}\n */`
+    })
+  ]
+}

packages/plugin-mirror/src/index.js

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+import { name, version } from '../package.json'
+
+export const lineValues = (start, end) => {
+  const { x: x1, y: y1 } = end
+  const { x: x2, y: y2 } = start
+  const c = x1 * y2 - x2 * y1
+  return [-(x1 - x2), y1 - y2, c]
+}
+
+export const mirrorGen = (start, end) => {
+  const [A, B, C] = lineValues(start, end)
+  return (point) => {
+    const { x, y } = point
+    const uNom = (B ** 2 - A ** 2) * x - 2 * A * B * y - 2 * A * C
+    const vNom = (A ** 2 - B ** 2) * y - 2 * A * B * x - 2 * B * C
+    const denom = A ** 2 + B ** 2
+    return [uNom / denom, vNom / denom]
+  }
+}
+
+export default {
+  name: name,
+  version: version,
+  hooks: {
+    preRender: function (svg) {
+      if (svg.attributes.get('freesewing:plugin-mirror') === false)
+        svg.attributes.set('freesewing:plugin-mirror', version)
+    }
+  },
+  macros: {
+    macros: {
+      mirror: function ({
+        mirror,
+        clone = true,
+        points = null,
+        paths = null,
+        prefix = 'mirrored',
+        nameFormat // unimplemented
+      }) {
+        const [start, end] = mirror
+        const mirrorPoint = mirrorGen(start, end)
+        const ops = ['from', 'to', 'cp1', 'cp2']
+
+        if (paths !== null) {
+          paths.forEach((path) => {
+            // find existing path id
+            // Find point name from path by looking in the list of all points?
+            let foundId = null
+            for (let id of Object.keys(this.paths)) {
+              if (this.paths[id] === path) {
+                foundId = id
+                break
+              }
+            }
+            if (clone && foundId !== null) {
+              path = clone ? path.clone() : path
+              this.paths[`${prefix}${foundId}`] = path
+            }
+            for (let op in path.ops) {
+              for (let type of ops) {
+                // Iterate over all possible path op points and clone/move point
+                const pathOp = path.ops[op][type]
+                if (typeof pathOp !== 'undefined') {
+                  ;[pathOp.x, pathOp.y] = mirrorPoint(pathOp)
+                  pathOp.attributes.set('mirrored', true)
+                }
+              }
+            }
+          })
+        }
+        if (points !== null) {
+          points.forEach((point) => {
+            if (clone) {
+              point = point.clone()
+            }
+            ;[point.x, point.y] = mirrorPoint(point)
+            point.attributes.set('mirrored', true)
+          })
+        }
+      }
+    }
+  }
+}

packages/plugin-mirror/tests/mirror.test.js

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+import freesewing from 'freesewing'
+import { version } from '../package.json'
+let chai = require('chai')
+let expect = chai.expect
+chai.use(require('chai-string'))
+let plugin = require('../dist/index.js')
+
+it('Should set the plugin name:version attribute', () => {
+  let pattern = new freesewing.Pattern().with(plugin)
+  pattern.render()
+  expect(pattern.svg.attributes.get('freesewing:plugin-mirror')).to.equal(version)
+})