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Proper clipping of degenerate polygons: #197

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Merged
Fil merged 3 commits into from
May 27, 2020
Merged

Proper clipping of degenerate polygons: #197

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Proper clipping of degenerate polygons:
Fil May 3, 2020
739e863
spurious else (since we returned)
Fil May 3, 2020
3064cb6
spurious requires
Fil May 3, 2020
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4 changes: 2 additions & 2 deletions src/clip/buffer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,8 @@ export default function() {
var lines = [],
line;
return {
point: function(x, y) {
line.push([x, y]);
point: function(x, y, m) {
line.push([x, y, m]);
},
lineStart: function() {
lines.push(line = []);
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13 changes: 4 additions & 9 deletions src/clip/circle.js
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Original file line number Diff line number Diff line change
Expand Up @@ -41,15 +41,10 @@ export default function(radius) {
? v ? 0 : code(lambda, phi)
: v ? code(lambda + (lambda < 0 ? pi : -pi), phi) : 0;
if (!point0 && (v00 = v0 = v)) stream.lineStart();
// Handle degeneracies.
// TODO ignore if not clipping polygons.
if (v !== v0) {
point2 = intersect(point0, point1);
if (!point2 || pointEqual(point0, point2) || pointEqual(point1, point2)) {
point1[0] += epsilon;
point1[1] += epsilon;
v = visible(point1[0], point1[1]);
}
if (!point2 || pointEqual(point0, point2) || pointEqual(point1, point2))
point1[2] = 1;
}
if (v !== v0) {
clean = 0;
Expand All @@ -61,7 +56,7 @@ export default function(radius) {
} else {
// inside going out
point2 = intersect(point0, point1);
stream.point(point2[0], point2[1]);
stream.point(point2[0], point2[1], 2);
stream.lineEnd();
}
point0 = point2;
Expand All @@ -80,7 +75,7 @@ export default function(radius) {
stream.point(t[1][0], t[1][1]);
stream.lineEnd();
stream.lineStart();
stream.point(t[0][0], t[0][1]);
stream.point(t[0][0], t[0][1], 3);
}
}
}
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16 changes: 9 additions & 7 deletions src/clip/rejoin.js
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import pointEqual from "../pointEqual.js";
import {epsilon} from "../math.js";

function Intersection(point, points, other, entry) {
this.x = point;
Expand All @@ -22,14 +23,15 @@ export default function(segments, compareIntersection, startInside, interpolate,
if ((n = segment.length - 1) <= 0) return;
var n, p0 = segment[0], p1 = segment[n], x;

// If the first and last points of a segment are coincident, then treat as a
// closed ring. TODO if all rings are closed, then the winding order of the
// exterior ring should be checked.
if (pointEqual(p0, p1)) {
stream.lineStart();
for (i = 0; i < n; ++i) stream.point((p0 = segment[i])[0], p0[1]);
stream.lineEnd();
return;
if (!p0[2] && !p1[2]) {
stream.lineStart();
for (i = 0; i < n; ++i) stream.point((p0 = segment[i])[0], p0[1]);
stream.lineEnd();
return;
}
// handle degenerate cases by moving the point
p1[0] += 2 * epsilon;
}

subject.push(x = new Intersection(p0, segment, null, true));
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16 changes: 16 additions & 0 deletions test/projection/clipcircle-test.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
var tape = require("tape"),
d3 = require("../../");

tape("projection.clipAngle() deals with degenerate polygons", function(test) {
// https://observablehq.com/d/495020ca139c39bd
var polygon = {
type: "Polygon",
coordinates: [ [[-120, -30],[0, -30],[0, -90],[0, -30],[120, -30],[-120, -30]] ]
};
var projection = d3.geoAzimuthalEqualArea()
.translate([0.5, 0.5])
.rotate([0, -90, 0])
.clipAngle(170);
test.equal(d3.geoPath(projection)(polygon).replace(/\.\d+/g,""), 'M0,249L0,238L0,216L21,219L45,219L71,215L98,207L127,193L141,184L155,173L168,161L181,148L192,133L202,117L211,100L218,83L224,65L228,48L230,30L231,13L229,-17L222,-45L212,-70L200,-90L187,-107L179,-127L167,-147L151,-168L130,-188L104,-206L89,-213L73,-220L55,-225L37,-229L19,-232L0,-233L-18,-232L-36,-229L-54,-225L-72,-220L-88,-213L-103,-206L-129,-188L-150,-168L-166,-147L-178,-127L-186,-107L-186,-107L-199,-90L-211,-70L-221,-45L-228,-17L-230,13L-229,30L-227,48L-223,65L-217,83L-210,100L-201,117L-191,133L-180,148L-167,161L-154,173L-140,184L-126,193L-97,207L-70,215L-44,219L-20,219L0,216L0,238L0,249L0,249L-25,247L-51,243L-76,236L-100,227L-123,215L-145,201L-165,185L-184,166L-200,146L-214,124L-226,101L-235,77L-242,52L-246,26L-248,0L-246,-25L-242,-51L-235,-76L-226,-100L-214,-123L-200,-145L-184,-165L-165,-184L-145,-200L-123,-214L-100,-226L-76,-235L-51,-242L-25,-246L0,-248L26,-246L52,-242L77,-235L101,-226L124,-214L146,-200L166,-184L185,-165L201,-145L215,-123L227,-100L236,-76L243,-51L247,-25L249,0L247,26L243,52L236,77L227,101L215,124L201,146L185,166L166,185L146,201L124,215L101,227L77,236L52,243L26,247Z');
test.end();
});