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jasondaviesjasondavies
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Add tests for d3.geom.polygon and fix centroid bug.
d3.geom.polygon(…).area() assumes screen pixel coordinates with (0, 0) at the top left, and y increasing going downwards. This results in a positive area for counterclockwise coordinates. Howver, the default centroid calculation was assuming "usual" Cartesian coordinates with y increasing going upwards, hence the centroid coordinates were incorrectly multiplied by -1. This fix won't affect d3.geo.path(…).centroid() as it passes a constant to d3.geom.centroid.
1 parent 0e0ba08 commit 3740741

4 files changed

Lines changed: 37 additions & 3 deletions

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‎d3.geom.js‎

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@@ -198,7 +198,7 @@ d3.geom.polygon = function(coordinates) {
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a,
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b,
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c;
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if (!arguments.length) k = 1 / (6 * coordinates.area());
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if (!arguments.length) k = -1 / (6 * coordinates.area());
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while (++i < n) {
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a = coordinates[i];
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b = coordinates[i + 1];

‎d3.geom.min.js‎

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‎src/geom/polygon.js‎

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@@ -21,7 +21,7 @@ d3.geom.polygon = function(coordinates) {
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a,
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b,
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c;
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if (!arguments.length) k = 1 / (6 * coordinates.area());
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if (!arguments.length) k = -1 / (6 * coordinates.area());
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while (++i < n) {
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a = coordinates[i];
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b = coordinates[i + 1];

‎test/geom/polygon-test.js‎

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require("../env");
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require("../../d3");
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require("../../d3.geom");
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var vows = require("vows"),
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assert = require("assert");
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var suite = vows.describe("d3.geom.polygon");
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suite.addBatch({
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"polygon": {
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topic: function() {
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return d3.geom.polygon;
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},
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"area": {
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"last point equal to start point": function(polygon) {
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assert.equal(polygon([[0, 0], [0, 1], [1, 1], [1, 0], [0, 0]]).area(), 1);
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},
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"implicitly ending at start point": function(polygon) {
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assert.equal(polygon([[0, 0], [0, 1], [1, 1], [1, 0]]).area(), 1);
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}
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},
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"centroid": {
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"last point equal to start point": function(polygon) {
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assert.deepEqual(polygon([[0, 0], [0, 1], [1, 1], [1, 0], [0, 0]]).centroid(), [.5, .5]);
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},
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"implicitly ending at start point": function(polygon) {
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assert.deepEqual(polygon([[0, 0], [0, 1], [1, 1], [1, 0]]).centroid(), [.5, .5]);
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}
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}
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}
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});
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suite.export(module);

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