42 lines
1.2 KiB
JavaScript
42 lines
1.2 KiB
JavaScript
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// Transforms the coordinates of each feature in the given tile from
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// mercator-projected space into (extent x extent) tile space.
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export default function transformTile(tile, extent) {
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if (tile.transformed) return tile;
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const z2 = 1 << tile.z;
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const tx = tile.x;
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const ty = tile.y;
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for (const feature of tile.features) {
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const geom = feature.geometry;
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const type = feature.type;
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feature.geometry = [];
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if (type === 1) {
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for (let j = 0; j < geom.length; j += 2) {
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feature.geometry.push(transformPoint(geom[j], geom[j + 1], extent, z2, tx, ty));
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}
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} else {
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for (let j = 0; j < geom.length; j++) {
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const ring = [];
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for (let k = 0; k < geom[j].length; k += 2) {
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ring.push(transformPoint(geom[j][k], geom[j][k + 1], extent, z2, tx, ty));
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}
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feature.geometry.push(ring);
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}
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}
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}
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tile.transformed = true;
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return tile;
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}
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function transformPoint(x, y, extent, z2, tx, ty) {
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return [
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Math.round(extent * (x * z2 - tx)),
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Math.round(extent * (y * z2 - ty))];
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}
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