Added Vector.isCollinearWith(Vector other).

Also added a test for it.

src/main/java/com/sk89q/worldedit/Vector.java

@@ -600,6 +600,43 @@ public class Vector {
         );
     }
 
+    public boolean isCollinearWith(Vector other) {
+        if (x == 0 && y == 0 && z == 0) {
+            // this is a zero vector
+            return true;
+        }
+
+        final double otherX = other.x;
+        final double otherY = other.y;
+        final double otherZ = other.z;
+
+        if (otherX == 0 && otherY == 0 && otherZ == 0) {
+            // other is a zero vector
+            return true;
+        }
+
+        if ((x == 0) != (otherX == 0)) return false;
+        if ((y == 0) != (otherY == 0)) return false;
+        if ((z == 0) != (otherZ == 0)) return false;
+
+        final double quotientX = otherX / x;
+        if (!Double.isNaN(quotientX)) {
+            return other.equals(multiply(quotientX));
+        }
+
+        final double quotientY = otherY / y;
+        if (!Double.isNaN(quotientY)) {
+            return other.equals(multiply(quotientY));
+        }
+
+        final double quotientZ = otherZ / z;
+        if (!Double.isNaN(quotientZ)) {
+            return other.equals(multiply(quotientZ));
+        }
+
+        throw new RuntimeException("This should not happen");
+    }
+
     /**
      * Get a block point from a point.
      *
@@ -643,7 +680,6 @@ public class Vector {
 
         Vector other = (Vector) obj;
         return other.getX() == this.x && other.getY() == this.y && other.getZ() == this.z;
-
     }
 
     /**

src/test/java/com/sk89q/worldedit/VectorTest.java

@@ -0,0 +1,70 @@
+package com.sk89q.worldedit;
+
+import org.junit.*;
+import static org.junit.Assert.*;
+
+public class VectorTest {
+    @Test
+    public void collinearityTest() {
+        assertCollinear(0,0,0, 0,0,0);
+
+        assertCollinear(0,0,0, 1,0,0);
+        assertCollinear(0,0,0, 0,1,0);
+        assertCollinear(0,0,0, 0,0,1);
+
+        assertCollinear(1,0,0, 0,0,0);
+        assertCollinear(0,1,0, 0,0,0);
+        assertCollinear(0,0,1, 0,0,0);
+
+        assertCollinear(1,0,0, 2,0,0);
+        assertNotCollinear(1,0,0, 0,1,0);
+
+        assertNotCollinear(2,2,2, 8,4,4);
+        assertCollinear(8,2,2, 8,2,2);
+        assertNotCollinear(4,2,4, 4,4,4);
+        assertNotCollinear(1,1,2, 4,8,2);
+        assertNotCollinear(4,1,8, 1,4,4);
+        assertCollinear(2,4,2, 1,2,1);
+        assertNotCollinear(2,2,4, 1,2,1);
+        assertNotCollinear(4,4,1, 4,4,4);
+        assertNotCollinear(4,1,4, 1,8,2);
+        assertCollinear(8,8,4, 4,4,2);
+        assertNotCollinear(2,1,8, 1,1,2);
+        assertNotCollinear(8,1,2, 2,1,2);
+        assertNotCollinear(4,4,8, 2,2,8);
+        assertNotCollinear(8,4,8, 1,4,8);
+        assertNotCollinear(2,2,2, 1,4,2);
+        assertNotCollinear(1,1,2, 8,8,2);
+        assertNotCollinear(4,4,8, 8,4,4);
+        assertNotCollinear(1,8,2, 4,4,4);
+        assertNotCollinear(8,4,2, 1,2,2);
+        assertNotCollinear(1,8,2, 8,1,4);
+        assertNotCollinear(4,8,1, 4,8,8);
+        assertNotCollinear(8,1,8, 8,8,8);
+        assertNotCollinear(8,4,1, 4,2,2);
+        assertNotCollinear(4,8,1, 4,2,1);
+        assertNotCollinear(8,8,1, 2,4,2);
+        assertCollinear(8,1,4, 8,1,4);
+        assertNotCollinear(4,1,1, 2,4,8);
+        assertNotCollinear(4,2,8, 1,4,1);
+        assertNotCollinear(1,8,2, 1,8,1);
+        assertNotCollinear(1,1,2, 4,2,2);
+    }
+
+    private void assertCollinear(double ax, double ay, double az, double bx, double by, double bz) {
+        final Vector a = new Vector(ax,ay,az);
+        final Vector b = new Vector(bx,by,bz);
+        assertTrue(a.isCollinearWith(b));
+        assertTrue(b.isCollinearWith(a));
+        assertTrue(a.multiply(-1).isCollinearWith(b));
+        assertTrue(a.isCollinearWith(b.multiply(-1)));
+    }
+    private void assertNotCollinear(double ax, double ay, double az, double bx, double by, double bz) {
+        final Vector a = new Vector(ax,ay,az);
+        final Vector b = new Vector(bx,by,bz);
+        assertFalse(a.isCollinearWith(b));
+        assertFalse(b.isCollinearWith(a));
+        assertFalse(a.multiply(-1).isCollinearWith(b));
+        assertFalse(a.isCollinearWith(b.multiply(-1)));
+    }
+}