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73 lines
2.3 KiB
73 lines
2.3 KiB
1 year ago
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import {cartesian, cartesianNormalizeInPlace, spherical} from "./cartesian";
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import constant from "./constant";
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import {acos, cos, degrees, epsilon, radians, sin, tau} from "./math";
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import {rotateRadians} from "./rotation";
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// Generates a circle centered at [0°, 0°], with a given radius and precision.
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export function circleStream(stream, radius, delta, direction, t0, t1) {
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if (!delta) return;
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var cosRadius = cos(radius),
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sinRadius = sin(radius),
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step = direction * delta;
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if (t0 == null) {
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t0 = radius + direction * tau;
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t1 = radius - step / 2;
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} else {
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t0 = circleRadius(cosRadius, t0);
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t1 = circleRadius(cosRadius, t1);
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if (direction > 0 ? t0 < t1 : t0 > t1) t0 += direction * tau;
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}
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for (var point, t = t0; direction > 0 ? t > t1 : t < t1; t -= step) {
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point = spherical([cosRadius, -sinRadius * cos(t), -sinRadius * sin(t)]);
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stream.point(point[0], point[1]);
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}
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}
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// Returns the signed angle of a cartesian point relative to [cosRadius, 0, 0].
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function circleRadius(cosRadius, point) {
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point = cartesian(point), point[0] -= cosRadius;
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cartesianNormalizeInPlace(point);
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var radius = acos(-point[1]);
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return ((-point[2] < 0 ? -radius : radius) + tau - epsilon) % tau;
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}
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export default function() {
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var center = constant([0, 0]),
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radius = constant(90),
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precision = constant(6),
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ring,
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rotate,
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stream = {point: point};
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function point(x, y) {
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ring.push(x = rotate(x, y));
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x[0] *= degrees, x[1] *= degrees;
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}
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function circle() {
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var c = center.apply(this, arguments),
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r = radius.apply(this, arguments) * radians,
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p = precision.apply(this, arguments) * radians;
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ring = [];
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rotate = rotateRadians(-c[0] * radians, -c[1] * radians, 0).invert;
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circleStream(stream, r, p, 1);
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c = {type: "Polygon", coordinates: [ring]};
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ring = rotate = null;
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return c;
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}
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circle.center = function(_) {
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return arguments.length ? (center = typeof _ === "function" ? _ : constant([+_[0], +_[1]]), circle) : center;
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};
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circle.radius = function(_) {
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return arguments.length ? (radius = typeof _ === "function" ? _ : constant(+_), circle) : radius;
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};
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circle.precision = function(_) {
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return arguments.length ? (precision = typeof _ === "function" ? _ : constant(+_), circle) : precision;
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};
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return circle;
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}
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