GeometryUtils: Fix reverse clockwise check

vtm-tests/test/org/oscim/utils/GeometryTest.java

@@ -0,0 +1,45 @@
+package org.oscim.utils;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.oscim.utils.geom.GeometryUtils;
+
+public class GeometryTest {
+
+    @Test
+    public void testIsTrisClockwise() {
+        float[] pA = new float[]{0, 0};
+        float[] pB = new float[]{1, 1};
+        float[] pC = new float[]{1, 0};
+
+        float area = GeometryUtils.isTrisClockwise(pA, pB, pC);
+        Assert.assertTrue(area > 0);
+
+        area = GeometryUtils.isTrisClockwise(pA, pC, pB);
+        Assert.assertTrue(area < 0);
+    }
+
+    @Test
+    public void testIsClockwise() {
+        float[] points = new float[]{0, 0, 1, 1, 1, 0};
+
+        float area = GeometryUtils.isClockwise(points, points.length);
+        Assert.assertTrue(area > 0);
+
+        points = new float[]{0, 0, 1, 0, 1, 1};
+        area = GeometryUtils.isClockwise(points, points.length);
+        Assert.assertTrue(area < 0);
+    }
+
+    @Test
+    public void testDotProduct() {
+        float[] p = {-1, 0, 0, 0, 0, 0};
+
+        for (int i = 0; i < 9; i++) {
+            p[4] = (float) Math.cos(Math.toRadians(i * 45));
+            p[5] = (float) Math.sin(Math.toRadians(i * 45));
+            System.out.println("\n> " + (i * 45) + " " + p[3] + ":" + p[4] + "\n="
+                    + GeometryUtils.dotProduct(p, 0, 2, 4));
+        }
+    }
+}

vtm/src/org/oscim/utils/geom/GeometryUtils.java

@@ -322,9 +322,9 @@ public final class GeometryUtils {
     public static float isClockwise(float[] points, int n) {
         float area = 0f;
         for (int i = 0; i < n - 2; i += 2) {
-            area += (points[i] * points[i + 3]) - (points[i + 1] * points[i + 2]);
+            area += (points[i + 1] * points[i + 2]) - (points[i] * points[i + 3]);
         }
-        area += (points[n - 2] * points[1]) - (points[n - 1] * points[0]);
+        area += (points[n - 1] * points[0]) - (points[n - 2] * points[1]);
 
         return 0.5f * area;
     }
@@ -400,15 +400,4 @@ public final class GeometryUtils {
         }
         return scaled;
     }
-
-    public static void main(String[] args) {
-        float[] p = {-1, 0, 0, 0, 0, 0};
-
-        for (int i = 0; i < 9; i++) {
-            p[4] = (float) Math.cos(Math.toRadians(i * 45));
-            p[5] = (float) Math.sin(Math.toRadians(i * 45));
-            System.out.println("\n> " + (i * 45) + " " + p[3] + ":" + p[4] + "\n="
-                    + dotProduct(p, 0, 2, 4));
-        }
-    }
 }