Add line segment-line segment intersection

CHANGES.md

@@ -5,6 +5,7 @@ Change Log
 
 ##### Additions :tada:
 * Added `Scene.invertClassificationSupported` for checking if invert classification is supported.
+* Added `computeLineSegmentLineSegmentIntersection` to `Intersections2D`. [#7228](https://github.com/AnalyticalGraphicsInc/Cesium/pull/7228)
 
 ### 1.51 - 2018-11-01
 

Source/Core/Intersections2D.js

@@ -1,9 +1,13 @@
 define([
+        './Cartesian2',
         './Cartesian3',
+        './Check',
         './defined',
         './DeveloperError'
     ], function(
+        Cartesian2,
         Cartesian3,
+        Check,
         defined,
         DeveloperError) {
     'use strict';
@@ -278,5 +282,60 @@ define([
         return new Cartesian3(l1, l2, l3);
     };
 
+    /**
+     * Compute the intersection between 2 line segments
+     *
+     * @param {Number} x00 The x coordinate of the first line's first vertex.
+     * @param {Number} y00 The y coordinate of the first line's first vertex.
+     * @param {Number} x01 The x coordinate of the first line's second vertex.
+     * @param {Number} y01 The y coordinate of the first line's second vertex.
+     * @param {Number} x10 The x coordinate of the second line's first vertex.
+     * @param {Number} y10 The y coordinate of the second line's first vertex.
+     * @param {Number} x11 The x coordinate of the second line's second vertex.
+     * @param {Number} y11 The y coordinate of the second line's second vertex.
+     * @param {Cartesian2} [result] The instance into to which to copy the result. If this parameter
+     *                     is undefined, a new instance is created and returned.
+     * @returns {Cartesian2} The intersection point, undefined if there is no intersection point or lines are coincident.
+     *
+     * @example
+     * var result = Cesium.Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 2.0, -1, 1, 1, 1);
+     * // result === new Cesium.Cartesian2(0.0, 1.0);
+     */
+    Intersections2D.computeLineSegmentLineSegmentIntersection = function(x00, y00, x01, y01, x10, y10, x11, y11, result) {
+        //>>includeStart('debug', pragmas.debug);
+        Check.typeOf.number('x00', x00);
+        Check.typeOf.number('y00', y00);
+        Check.typeOf.number('x01', x01);
+        Check.typeOf.number('y01', y01);
+        Check.typeOf.number('x10', x10);
+        Check.typeOf.number('y10', y10);
+        Check.typeOf.number('x11', x11);
+        Check.typeOf.number('y11', y11);
+        //>>includeEnd('debug');
+
+        var numerator1A = (x11 - x10) * (y00 - y10) - (y11 - y10) * (x00 - x10);
+        var numerator1B = (x01 - x00) * (y00 - y10) - (y01 - y00) * (x00 - x10);
+        var denominator1 = (y11 - y10) * (x01 - x00) - (x11 - x10) * (y01 - y00);
+
+        // If denominator = 0, then lines are parallel. If denominator = 0 and both numerators are 0, then coincident
+        if (denominator1 === 0) {
+            return;
+        }
+
+        var ua1 = numerator1A / denominator1;
+        var ub1 = numerator1B / denominator1;
+
+        if (ua1 >= 0 && ua1 <= 1 && ub1 >= 0 && ub1 <= 1) {
+            if (!defined(result)) {
+                result = new Cartesian2();
+            }
+
+            result.x = x00 + ua1 * (x01 - x00);
+            result.y = y00 + ua1 * (y01 - y00);
+
+            return result;
+        }
+    };
+
     return Intersections2D;
 });

Specs/Core/Intersections2DSpec.js

@@ -288,4 +288,58 @@ defineSuite([
             expect(result3.z).toBeGreaterThan(0.0);
         });
     });
+
+    describe('computeLineSegmentLineSegmentIntersection', function() {
+        it('returns the correct result for intersection point', function() {
+            var intersection0 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 2.0, -1.0, 1.0, 1.0, 1.0);
+            expect(intersection0.x).toEqualEpsilon(0.0, 1e-15);
+            expect(intersection0.y).toEqualEpsilon(1.0, 1e-15);
+
+            var intersection1 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 10.0, 5.0, 0.0, 5.0, 10.0, 0.0);
+            expect(intersection1.x).toEqualEpsilon(5.0, 1e-15);
+            expect(intersection1.y).toEqualEpsilon(2.5, 1e-15);
+
+            var intersection2 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, -5.0, 4.0, 3.0, -2.0, 1.0, 4.0, -2.0);
+            expect(intersection2.x).toEqualEpsilon(2.0, 1e-15);
+            expect(intersection2.y).toEqualEpsilon(-1.0, 1e-15);
+        });
+
+        it('returns the correct result for intersection point on a vertex', function() {
+            var intersection0 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 2.0, -1.0, 0.0, 1.0, 0.0);
+            expect(intersection0.x).toEqualEpsilon(0.0, 1e-15);
+            expect(intersection0.y).toEqualEpsilon(0.0, 1e-15);
+
+            var intersection1 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 2.0, 0.0);
+            expect(intersection1.x).toEqualEpsilon(1.0, 1e-15);
+            expect(intersection1.y).toEqualEpsilon(1.0, 1e-15);
+
+            var intersection2 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 4.0, 3.0, 5.0, 0.0, 4.0, 3.0);
+            expect(intersection2.x).toEqualEpsilon(4.0, 1e-15);
+            expect(intersection2.y).toEqualEpsilon(3.0, 1e-15);
+        });
+
+        it('returns undefined for non-intersecting lines', function() {
+            var intersection0 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 5.0, 0.1, 4.8, 5.0, 0.0);
+            expect(intersection0).toBeUndefined();
+
+            var intersection1 = Intersections2D.computeLineSegmentLineSegmentIntersection(10.0, 0.0, 0.0, -10.0, 0.0, 0.0, -8.0, -8.0);
+            expect(intersection1).toBeUndefined();
+        });
+
+        it('returns undefined for parallel lines', function() {
+            var intersection0 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 2.0, 1.0, 1.0, 1.0, 4.0);
+            expect(intersection0).toBeUndefined();
+
+            var intersection1 = Intersections2D.computeLineSegmentLineSegmentIntersection(1.0, 1.0, 4.0, 4.0, 0.0, 0.0, 3.0, 3.0);
+            expect(intersection1).toBeUndefined();
+        });
+
+        it('returns undefined for coincident lines', function() {
+            var intersection0 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 2.0, 0.0, 1.0, 0.0, 4.0);
+            expect(intersection0).toBeUndefined();
+
+            var intersection1 = Intersections2D.computeLineSegmentLineSegmentIntersection(0.0, 0.0, 0.0, 2.0, 0.0, 0.0, 0.0, 2.0);
+            expect(intersection1).toBeUndefined();
+        });
+    });
 });