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Use a special data structure for transferring feature id maps to the …
…main thread (#7132) * introduce a special structure for transfering feature id map * fix overflow in feature state offsets * simplify feature position map * fix buffer offset for feature state, more resilient structure * add a unit test for feature map
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// @flow | ||
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import { register } from '../util/web_worker_transfer'; | ||
import assert from 'assert'; | ||
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type SerializedFeaturePositionMap = { | ||
ids: Float64Array; | ||
positions: Uint32Array; | ||
}; | ||
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type FeaturePosition = { | ||
index: number; | ||
start: number; | ||
end: number; | ||
}; | ||
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// A transferable data structure that maps feature ids to their indices and buffer offsets | ||
export default class FeaturePositionMap { | ||
ids: Array<number>; | ||
positions: Array<number>; | ||
indexed: boolean; | ||
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constructor() { | ||
this.ids = []; | ||
this.positions = []; | ||
this.indexed = false; | ||
} | ||
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add(id: number, index: number, start: number, end: number) { | ||
this.ids.push(id); | ||
this.positions.push(index, start, end); | ||
} | ||
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getPositions(id: number): Array<FeaturePosition> { | ||
assert(this.indexed); | ||
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// binary search for the first occurrence of id in this.ids; | ||
// relies on ids/positions being sorted by id, which happens in serialization | ||
let i = 0; | ||
let j = this.ids.length - 1; | ||
while (i < j) { | ||
const m = (i + j) >> 1; | ||
if (this.ids[m] >= id) { | ||
j = m; | ||
} else { | ||
i = m + 1; | ||
} | ||
} | ||
const positions = []; | ||
while (this.ids[i] === id) { | ||
const index = this.positions[3 * i]; | ||
const start = this.positions[3 * i + 1]; | ||
const end = this.positions[3 * i + 2]; | ||
positions.push({index, start, end}); | ||
i++; | ||
} | ||
return positions; | ||
} | ||
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static serialize(map: FeaturePositionMap, transferables: Array<ArrayBuffer>): SerializedFeaturePositionMap { | ||
const ids = new Float64Array(map.ids); | ||
const positions = new Uint32Array(map.positions); | ||
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sort(ids, positions, 0, ids.length - 1); | ||
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transferables.push(ids.buffer, positions.buffer); | ||
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return {ids, positions}; | ||
} | ||
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static deserialize(obj: SerializedFeaturePositionMap): FeaturePositionMap { | ||
const map = new FeaturePositionMap(); | ||
// after transferring, we only use these arrays statically (no pushes), | ||
// so TypedArray vs Array distinction that flow points out doesn't matter | ||
map.ids = (obj.ids: any); | ||
map.positions = (obj.positions: any); | ||
map.indexed = true; | ||
return map; | ||
} | ||
} | ||
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// custom quicksort that sorts ids, indices and offsets together (by ids) | ||
function sort(ids, positions, left, right) { | ||
if (left >= right) return; | ||
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const pivot = ids[(left + right) >> 1]; | ||
let i = left - 1; | ||
let j = right + 1; | ||
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while (true) { | ||
do i++; while (ids[i] < pivot); | ||
do j--; while (ids[j] > pivot); | ||
if (i >= j) break; | ||
swap(ids, i, j); | ||
swap(positions, 3 * i, 3 * j); | ||
swap(positions, 3 * i + 1, 3 * j + 1); | ||
swap(positions, 3 * i + 2, 3 * j + 2); | ||
} | ||
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sort(ids, positions, left, j); | ||
sort(ids, positions, j + 1, right); | ||
} | ||
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function swap(arr, i, j) { | ||
const tmp = arr[i]; | ||
arr[i] = arr[j]; | ||
arr[j] = tmp; | ||
} | ||
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register('FeaturePositionMap', FeaturePositionMap); |
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import { test } from 'mapbox-gl-js-test'; | ||
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import FeatureMap from '../../../src/data/feature_position_map'; | ||
import { serialize, deserialize } from '../../../src/util/web_worker_transfer'; | ||
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test('FeaturePositionMap', (t) => { | ||
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test('Can be queried after serialization/deserialization', (t) => { | ||
const featureMap = new FeatureMap(); | ||
featureMap.add(7, 1, 0, 1); | ||
featureMap.add(3, 2, 1, 2); | ||
featureMap.add(7, 3, 2, 3); | ||
featureMap.add(4, 4, 3, 4); | ||
featureMap.add(2, 5, 4, 5); | ||
featureMap.add(7, 6, 5, 7); | ||
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const featureMap2 = deserialize(serialize(featureMap, [])); | ||
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const compareIndex = (a, b) => a.index - b.index; | ||
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t.same(featureMap2.getPositions(7).sort(compareIndex), [ | ||
{index: 1, start: 0, end: 1}, | ||
{index: 3, start: 2, end: 3}, | ||
{index: 6, start: 5, end: 7} | ||
].sort(compareIndex)); | ||
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t.end(); | ||
}); | ||
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test('Can not be queried before serialization/deserialization', (t) => { | ||
const featureMap = new FeatureMap(); | ||
featureMap.add(0, 1, 2, 3); | ||
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t.throws(() => { | ||
featureMap.getPositions(0); | ||
}); | ||
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t.end(); | ||
}); | ||
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t.end(); | ||
}); |