A bunch of add/substract to syncmake i.Point with f/d.Point.

Closes #24.

src/main/java/pythagoras/i/AbstractPoint.java

@@ -10,26 +10,51 @@ package pythagoras.i;
  */
 public abstract class AbstractPoint implements IPoint
 {
-    @Override // from interface IPoint
+    @Override // from IPoint
     public int distanceSq (int px, int py) {
         return Points.distanceSq(x(), y(), px, py);
     }
 
-    @Override // from interface IPoint
+    @Override // from IPoint
     public int distanceSq (IPoint p) {
         return Points.distanceSq(x(), y(), p.x(), p.y());
     }
 
-    @Override // from interface IPoint
+    @Override // from IPoint
     public int distance (int px, int py) {
         return Points.distance(x(), y(), px, py);
     }
 
-    @Override // from interface IPoint
+    @Override // from IPoint
     public int distance (IPoint p) {
         return Points.distance(x(), y(), p.x(), p.y());
     }
 
+    @Override // from IPoint
+    public Point add (int x, int y) {
+        return new Point(x() + x, y() + y);
+    }
+
+    @Override // from IPoint
+    public Point add (int x, int y, Point result) {
+        return result.set(x() + x, y() + y);
+    }
+
+    @Override // from IPoint
+    public Point subtract (int x, int y) {
+        return subtract(x, y, new Point());
+    }
+
+    @Override
+    public Point subtract (int x, int y, Point result) {
+        return result.set(x() - x, y() - y);
+    }
+
+    @Override
+    public Point subtract (IPoint other, Point result) {
+        return subtract(other.x(), other.y(), result);
+    }
+
     @Override // from interface IPoint
     public Point clone () {
         return new Point(this);

src/main/java/pythagoras/i/IPoint.java

@@ -27,6 +27,26 @@ public interface IPoint extends Cloneable
     /** Returns the Euclidian distance between this point and the supplied point. */
     int distance (IPoint p);
 
+    /** Translates this point by the specified offset.
+     * @return a new point containing the result. */
+    Point add (int x, int y);
+
+    /** Translates this point by the specified offset and stores the result in the object provided.
+     * @return a reference to the result, for chaining. */
+    Point add (int x, int y, Point result);
+
+    /** Subtracts the supplied point from {@code this}.
+     * @return a new point containing the result. */
+    Point subtract (int x, int y);
+
+    /** Subtracts the supplied point from {@code this} and stores the result in {@code result}.
+     * @return a reference to the result, for chaining. */
+    Point subtract (int x, int y, Point result);
+
+    /** Subtracts the supplied point from {@code this} and stores the result in {@code result}.
+     * @return a reference to the result, for chaining. */
+    Point subtract (IPoint other, Point result);
+
     /** Returns a mutable copy of this point. */
     Point clone ();
 }

src/main/java/pythagoras/i/Point.java

@@ -67,6 +67,32 @@ public class Point extends AbstractPoint implements Serializable
         y += dy;
     }
 
+    /** Sets the coordinates of this point to be equal to those of the supplied point.
+     * @return a reference to this this, for chaining. */
+    public Point set (IPoint p) {
+        return set(p.x(), p.y());
+    }
+
+    /** Sets the coordinates of this point to the supplied values.
+     * @return a reference to this this, for chaining. */
+    public Point set (int x, int y) {
+        this.x = x;
+        this.y = y;
+        return this;
+    }
+
+    /** Translates this point by the specified offset.
+     * @return a reference to this point, for chaining. */
+    public Point addLocal (int dx, int dy) {
+        return add(dx, dy, this);
+    }
+
+    /** Subtracts the supplied x/y from this point.
+     * @return a reference to this point, for chaining. */
+    public Point subtractLocal (int x, int y) {
+        return subtract(x, y, this);
+    }
+
     @Override // from interface IPoint
     public int x () {
         return x;