2e:null 2f:["$","title",null,{"children":"Review of Formation Flying RFC for Endless Sky | Thomas Ballinger | Observable"}] 34:Ta14,md`## Making formations Once I had this simple parser hooked up I tried writing a few formations that I wanted (until this point I had just been playing with numbers until things looked cool). **One line** I want a line of fighter directly behind me. I'll make my line start at (0, -10) based on my diagram, and us a spacing of 10. This is easy! It felt a little odd to use angle when I had been using x/y instead; but in the real spec I think I could have used either, I just didn't implement polar coordinates. ~~~ formation "cone thing" line start 0 -10 slots 10 angle 0 spacing 10 ~~~ **A triangle** I figure I can make my lines horizontal or vertical. If each line is vertical I think I'll need three lines, one for the center one to repeat on each side? This would be for a triangle that grows outwards. *I'd want to use slots of -1 in my repeat clause to make sure I really build a triangle instead of a v, but that doesn't work; you can only add more in each row repeat of a row, not fewer.* ~~~ formation "foo" line start 0 -10 slots 5 angle 0 spacing 10 line start 20 -10 slots 5 angle 0 spacing 10 repeat start 20 -20 line start -20 -10 slots 5 angle 0 spacing 10 repeat start -20 -20 ~~~ ${await FileAttachment("2020-06-12 15.33.56.gif").image()} This was the wrong way to do this though, if I want a triangle I should build it in layers from the top. ~~~ formation "foo" line start -10 -10 slots 3 angle 225 spacing 14 repeat start -10 -10 slots 2 ~~~ ${await FileAttachment("2020-06-12 15.50.59.gif").image()} It confused me at first that I had to specify the angle with respect to the angle from my ship to the first escort's ship, but I could have used a end point instead and then it would have been pretty straightforward. (but I didn't implement that) **V** I'm thinking two lines of one ship each? ~~~ formation "foo" line start -10 -10 slots 1 angle 0 spacing 10 repeat start -10 -10 line start 10 -10 slots 1 angle 100 spacing 10 repeat start 10 -10 ~~~ Pretty easy! **Buddy ship** I want my buddy right over my shoulder, and everyone else off behind us both. I'm thinking one line for my buddy, another for a triangle or line that's offset a bit. ~~~ formation "foo" line start -10 0 slots 1 angle 0 spacing 10 line start -5 -30 slots 1 angle 100 spacing 10 repeat start 0 -10 ~~~ No problem! ${await FileAttachment("2020-06-12 15.56.31.gif").image()} **A circle** I didn't try to do a circle because I didn't implement arcs. `35:T55f,md`## Questions Question about [the proposal](https://github.com/EndlessSkyCommunity/endless-sky/pull/52/files): - The point of symmetry is only used to help ships find a better position when ~~they are far out of position~~ edit: turns out it's if you turn quickly. If an asymmetric formation is reported as symmetric then the formation may be flipped on this axis, if it makes it easier for escorts to get to that spot. I was confused at first because this property seems useful even when a formation is not symmetric; I thought of it as "allow flip." - petervdmeer: interesting, post that on the PR if you want to suggest it - What rotational symmetry should be used for a circle? 1? Would that work? - Would it be simpler to specify how many pieces you want the circle cut up into, n = d/360? - thinking about this more, I dont' see why one is better than the other. - Are end and angle mutually exclusive? Will repeat be inferred from spacing and end? I'd rather get rid of one of the two of angle and end. - From the spec: > If a line has an end-coordinate and slots and spacing set, then the end coordinate is only used to determine the direction. - Some things are mutually exclusive. How will than be handled? Some validation on load? I think validating to prevent both from being used may be more useful than allowing both and having a defined behavior. `36:T917,// Copied from https://github.com/petervdmeer/endless-sky/blob/e008bb6f7ffae85f213b1622f05d087ea7e7cc4f/source/FormationPattern.cpp class FormationPattern { constructor(name) { this.lines = []; } static load(str) { const { title, lines, arcs } = parseFormation(str); const fp = new FormationPattern(title); fp.lines = lines; return fp; } // Get the next line that has space for placement of ships. Returns -1 if none found/available. NextLineAndRing(ring, lineNr) { // All lines participate in the first initial ring. if (ring == 0 && lineNr < this.lines.length - 1) return { ring, lineNr: lineNr + 1 }; // For later rings only lines that repeat will participate. let linesScanned = 0; while (linesScanned <= this.lines.length) { lineNr = lineNr + 1; if (lineNr >= this.lines.length) { lineNr = lineNr % this.lines.length; ring += 1; } if (this.lines[lineNr].slotsIncrease >= 0) return { ring, lineNr }; // Safety mechanism to avoid endless loops if the formation has a limited size. linesScanned++; } return { ring: -1, lineNr: -1 }; } // Get the number of positions on a line for the given ring. LineSlots(ring, lineNr) { if (lineNr >= this.lines.length) return 0; // Retrieve the relevant line. const line = this.lines[lineNr]; // For the first ring, only the initial positions are relevant. if (ring == 0) return line.initialSlots; // If we are in a later ring, then skip lines that don't repeat. if (line.slotsIncrease < 0) return 0; return line.initialSlots + line.slotsIncrease * ring; } // Get a formation position based on ring, line-number and position on the line. Position(ring, lineNr, lineSlot) { if (lineNr >= this.lines.length) return Point(); const line = this.lines[lineNr]; // Calculate position based on the initial anchor, the ring on which we are, the // line-position on the current line and the rotation of the current line. return Point( line.anchor.x + line.repeatVector.x * ring + Rotate(line.direction, Point(0, -line.spacing * lineSlot)).x, line.anchor.y + line.repeatVector.y * ring + Rotate(line.direction, Point(0, -line.spacing * lineSlot)).y ); } }37:T803,parseFormation = src => { let title; let lines = []; let arcs = []; let curLineOrArc; let context = []; let lastIndentation = 0; for (const line of src.split('\n')) { if (!line.trim()) { continue; } const indentation = line.lastIndexOf('\t') + 1; context = context.slice(0, indentation); if (line.startsWith('formation')) { title = line.match(/formation "(.*)"/)[1]; context.push('formation'); } else if (line.trim().startsWith('symmetry')) { context.push('symmetry'); // this parser ignores symmetry continue; } else if (line.trim().startsWith("line")) { context.push('line'); curLineOrArc = {}; lines.push(curLineOrArc); continue; } else if (line.trim().startsWith("repeat")) { const prev = curLineOrArc; context.push('repeat'); curLineOrArc = {}; prev.repeat = curLineOrArc; continue; } else if (context[0] == 'symmetry') { // this parser ignores symmetry continue; } else if ( context[context.length - 1] == 'line' || (context[context.length - 1] == 'repeat' && context[context.length - 2] == 'line') ) { if (line.trim().startsWith('start')) { const [, polar, x, y] = line.match(/start (polar)?[ ]?(\S+) (\S+)/); curLineOrArc.anchor = { polar: !!polar, x: parseInt(x), y: parseInt(y) }; } else if (line.trim().startsWith('slots')) { const [, slots] = line.match(/slots (\S+)/); curLineOrArc.slots = parseInt(slots); } else if (line.trim().startsWith('angle')) { const [, direction] = line.match(/angle (\S+)/); curLineOrArc.direction = parseInt(direction); } else if (line.trim().startsWith('spacing')) { const [, spacing] = line.match(/spacing (\S+)/); curLineOrArc.spacing = parseInt(spacing); } } } return { title, lines: lines.map(l => new Line(l.anchor, l.slots, l.direction, l.spacing, l.repeat)), arcs }; }38:[{"id":"78d996b7210a87cdddd65ac1437284b3408413be57ce6e4cab882e4b193fadf34672aabbc5a7c77bd5ff323218ad6c4581df2afe47760a69f6805e24dd3d4038","href":"https://static.observableusercontent.com/files/78d996b7210a87cdddd65ac1437284b3408413be57ce6e4cab882e4b193fadf34672aabbc5a7c77bd5ff323218ad6c4581df2afe47760a69f6805e24dd3d4038","name":"Screen Shot 2020-06-12 at 10.35.42 AM.png","type":"image/png","lastModified":1591983417899.573,"size":1949863},{"id":"5ec033bddd43a94ca8eccfa8819ff927eeecb459a73f1d964c226db4425e415981f0ad655269a5d93c657854ed1141c0557e66f81fb6a912ecdc3469ff538cf2","href":"https://static.observableusercontent.com/files/5ec033bddd43a94ca8eccfa8819ff927eeecb459a73f1d964c226db4425e415981f0ad655269a5d93c657854ed1141c0557e66f81fb6a912ecdc3469ff538cf2","name":"2020-06-12 15.56.31.gif","type":"image/gif","lastModified":1592002637802.019,"size":68561},{"id":"73d4b1e830a7750b011a2291ecafa14e0237253df3b3c5fb7853ee67bae1a3ae9f635d5a9a786c215a5c0b1488141958c7cc13b0e2b652d7d293c56192775818","href":"https://static.observableusercontent.com/files/73d4b1e830a7750b011a2291ecafa14e0237253df3b3c5fb7853ee67bae1a3ae9f635d5a9a786c215a5c0b1488141958c7cc13b0e2b652d7d293c56192775818","name":"2020-06-12 15.50.59.gif","type":"image/gif","lastModified":1592002289855.165,"size":122937},{"id":"bfe23f78994feb0224c29aa90499002408a604e6b93305193310ce345cc0e82a674f019b03e813ba40a20ed4c8c9b6150942cd00e149b747e283782464a772b0","href":"https://static.observableusercontent.com/files/bfe23f78994feb0224c29aa90499002408a604e6b93305193310ce345cc0e82a674f019b03e813ba40a20ed4c8c9b6150942cd00e149b747e283782464a772b0","name":"2020-06-12 15.33.56.gif","type":"image/gif","lastModified":1592001273901.545,"size":156141}] 32:{"id":"aa9298a68f050086","slug":"review-of-formation-flying-rfc-for-endless-sky","title":"Review of Formation Flying RFC for Endless Sky","thumbnail":"5b2c00dc1672c55212d5bad6281157da727ac50ecd6b355b4d7b3b9e9c5436fb","access_level":"public","create_time":"$D2020-06-12T15:56:26.217Z","update_time":"$D2020-06-14T14:43:20.913Z","view_time":null,"first_public_time":"$D2020-06-12T21:19:08.059Z","has_unpublished_edits":null,"fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"99d0de2d65d767e9","login":"ballingt-personal","name":"Thomas Ballinger","avatar_url":"https://avatars-next.observableusercontent.com/8ad92a493f85feedf6531556fe220dd29149c2e77f7de99419eb9ad4a60dc179","tier":"starter_2024"},"version":980,"publish_version":980,"role":null,"authored":false,"authors":[{"type":"individual","id":"f4a1ec06e8e5f9ad","login":"ballingt-personal","name":"Thomas Ballinger","avatar_url":"https://avatars-next.observableusercontent.com/8ad92a493f85feedf6531556fe220dd29149c2e77f7de99419eb9ad4a60dc179","tier":null}],"members":[{"type":"individual","id":"f4a1ec06e8e5f9ad","login":"ballingt-personal","name":"Thomas Ballinger","avatar_url":"https://avatars-next.observableusercontent.com/8ad92a493f85feedf6531556fe220dd29149c2e77f7de99419eb9ad4a60dc179","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":1,"collection":null,"type":"notebook","body":{"title":"Review of Formation Flying RFC for Endless Sky","cells":[{"id":11,"value":"md`# Review of Formation Flying RFC for Endless Sky\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":171,"value":"md`## Comparison to the old syntax\n\nThe examples with the old syntax in https://github.com/endless-sky/endless-sky/pull/4471 look like this:\n~~~\nformation \"foo\"\n line 2 0 3 270\n spacing 2.8\n repeat 7 9\n~~~\nvs the new spec \n~~~\nformation \"foo\"\n line\n start 2 0\n slots 3\n angle 270\n spacing 2.8\n repeat\n start 7 9\n~~~\nI *think* these two are equivalent, it wasn't exactly clear.\n\nAt first glance I prefer the new syntax: it tells me what the parameters mean.\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":85,"value":"oldSpecText = html`\n

Old examples (click to expand)

\n${await (await fetch(\n  'https://raw.githubusercontent.com/petervdmeer/endless-sky/formation_flying/data/formations.txt'\n)).text()}\n

\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":165,"value":"md`## Coordinate system`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":152,"value":"FileAttachment(\"Screen Shot 2020-06-12 at 10.35.42 AM.png\").image()","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":27,"value":"md`### Trying it out\n\nI've written a quick, incomplete parser below to try out this syntax.\n\n

\n Warning: This parser is missing lots of features from [the spec](https://github.com/EndlessSkyCommunity/endless-sky/pull/52), including but not limited to arc, polar, end, skip, repeat angle, and repeat spacing.\n

\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":711,"value":"viewof specChoice.bind(\n radio({\n title: 'Formation',\n options: [\n { label: 'V', value: 'coneThing' },\n { label: 'Lines behind', value: 'linesBehindMe' },\n { label: 'Simple spec', value: 'simpleSpec' }\n ],\n value: 'simpleSpec'\n })\n)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":76,"value":"viewof customSpec = textarea({ rows: 10, value: specPresets[specChoice] })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":72,"value":"viewof numShips = slider({\n min: 0,\n max: 100,\n value: 15,\n step: 1,\n title: 'number of escorts'\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":547,"value":"show(customSpec, numShips)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":227,"value":"html`

\n${FormationPattern.load(spec).lines.map(\n line =>\n html`

Line: (${line.anchor.x}, ${line.anchor.y}), slots: ${\n line.initialSlots\n }, angle: ${line.direction}, repeat: ${line.repeatVector &&\n line.repeatVector &&\n `(${line.repeatVector.x}, ${line.repeatVector.y})`}

`\n)}\n

`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":475,"value":"getPositions(spec, numShips).map(p => `${p.x.toFixed(2)}, ${p.y.toFixed(2)}`)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":284,"value":"$34","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":8,"value":"$35","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":289,"value":"md`## Other thoughts\n\nI think it would be neat if positions in a formation were not always replaced; leaving some space allows you to assess casualities in your own and especially other fleets.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":624,"value":"md`## Background`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":31,"value":"md`### Videos\n\n${loopedYouTube('W0RrTRSSqGs', true)}\n\n${loopedYouTube('iuwoZN2gaSI', true)}\n\n${loopedYouTube('T6dCA2hmOlk', true)}\n\nFor more see [this PR on GitHub](https://github.com/endless-sky/endless-sky/pull/4471)\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":702,"value":"md`### Formations`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":84,"value":"simpleSpec = `formation \"foo\"\n line\n start -10 -10\n slots 3\n angle 225\n spacing 14\n repeat\n start -10 -10\n slots 2`.replace(/ /g, '\\t')","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":705,"value":"coneThing = `formation \"cone thing\"\n\\tline\n\\t\\tstart -10 -10\n\\t\\tslots 1\n\\t\\tangle 0\n\\t\\tspacing 10\n\\t\\trepeat\n\\t\\t\\tstart -10 -10\n\\tline\n\\t\\tstart 10 -10\n\\t\\tslots 1\n\\t\\tangle 100\n\\t\\tspacing 10\n\\t\\trepeat\n\\t\\t\\tstart 10 -10`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":721,"value":"linesBehindMe = `formation \"foo\"\n\tline\n\t\tstart 0 -10\n\t\tslots 4\n\t\tangle 0\n\t\tspacing 10\n\tline\n\t\tstart 20 -10\n\t\tslots 5\n\t\tangle 0\n\t\tspacing 10\n\t\trepeat\n\t\t\tstart 20 -20\n\tline\n\t\tstart -20 -10\n\t\tslots 5\n\t\tangle 0\n\t\tspacing 10\n\t\trepeat\n\t\t\tstart -20 -20`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":40,"value":"md`## Appendix\nThe JavaScript code that makes this notebook run.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":735,"value":"spec = specPresets[specChoice]","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":819,"value":"specPresets = ({\n linesBehindMe,\n coneThing,\n simpleSpec\n})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":382,"value":"Rotate = (angle, point) => {\n const rad = (Math.PI / 180) * angle;\n const x = Math.cos(rad) * point.x + Math.sin(rad) * point.y;\n const y = Math.cos(rad) * point.y - Math.sin(rad) * point.y;\n return Point(x, y);\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":294,"value":"$36","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":304,"value":"Point = (x, y) => new PointClass(x, y)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":377,"value":"class Line {\n constructor(anchor, slots, direction, spacing, repeat) {\n this.anchor = anchor;\n this.initialSlots = slots;\n this.direction = direction;\n this.spacing = spacing;\n this.repeatVector =\n repeat && repeat.anchor\n ? Point(repeat.anchor.x, repeat.anchor.y)\n : Point(0, 0);\n this.slotsIncrease = repeat ? repeat.slots || 0 : -1;\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":417,"value":"class PointClass {\n constructor(x, y) {\n this.x = x;\n this.y = y;\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":107,"value":"$37","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":45,"value":"loopedYouTube = (id, muted = true) =>\n html``","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":438,"value":"{\n // side effect to make tab key enter tabs\n viewof specChoice;\n var textareas = document.getElementsByTagName('textarea');\n var count = textareas.length;\n for (var i = 0; i < count; i++) {\n textareas[i].onkeydown = function(e) {\n if (e.keyCode == 9 || e.which == 9) {\n e.preventDefault();\n var s = this.selectionStart;\n this.value =\n this.value.substring(0, this.selectionStart) +\n \"\\t\" +\n this.value.substring(this.selectionEnd);\n this.selectionEnd = s + 1;\n }\n };\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":479,"value":"show = (spec, n) => {\n const positions = getPositions(spec, n);\n\n let seed = 1;\n function random() {\n var x = Math.sin(seed++) * 10000;\n return x - Math.floor(x);\n }\n\n return html`\n\n`;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":317,"value":"getPositions = (spec, n) => {\n const fp = FormationPattern.load(spec);\n\n let curRing = 0;\n let curLine = -1;\n const positions = [];\n while (true) {\n const { ring, lineNr } = fp.NextLineAndRing(curRing, curLine);\n curRing = ring;\n curLine = lineNr;\n const slots = fp.LineSlots(curRing, curLine);\n for (const pos of [...Array(slots).keys()].map(s =>\n fp.Position(curRing, curLine, s)\n )) {\n if (positions.length < n) {\n positions.push(pos);\n } else {\n return positions;\n }\n }\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":839,"value":"viewof specChoice = new View('simpleSpec')","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":836,"value":"import { View, bind } from '@mbostock/synchronized-views'","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":68,"value":"import { slider, textarea, radio } from '@jashkenas/inputs'","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W38","stdlib":"1","titling":"auto"}} 33:"$32:body"