Add parent relationship to GraphicsObject

src/edu/macalester/graphics/CanvasWindow.java

@@ -78,7 +78,7 @@ public class CanvasWindow {
 
     private final Canvas canvas;
     private final JFrame windowFrame;
-    private final GraphicsGroup content = new GraphicsGroup();
+    private final GraphicsGroup content;
     private Set<JComponent> embeddedComponents = Set.of();
     private final Rectangle background;
 
@@ -101,7 +101,12 @@ public class CanvasWindow {
      * @param windowHeight The height of the window's content area
      */
     public CanvasWindow(String title, int windowWidth, int windowHeight) {
-        content.setCanvas(this);  // propagates to descendants
+        content = new GraphicsGroup() {
+            @Override
+            public CanvasWindow getCanvas() {
+                return CanvasWindow.this;
+            }
+        };
 
         // We use a Rectangle for the background because canvas.setBackground() triggers spurious
         // repaints, whereas this approach puts background color changes into the same paint cycle

src/edu/macalester/graphics/FrameRateReporter.java

@@ -6,7 +6,7 @@ public class FrameRateReporter {
     private int framesSinceLastReport = 0;
     private long timeOfLastReport = System.currentTimeMillis();
 
-    public void tick() {
+    public synchronized void tick() {
         if (!enabled) {
             return;
         }

src/edu/macalester/graphics/GraphicsGroup.java

@@ -13,7 +13,7 @@
  * The group defines its own coordinate system, so the positions of objects added to it are relative
  * to the whole group's position.
  * <p>
- * Calling {@link setPosition(Point)} on a GraphicsGroup sets where the group’s local (0,0) shows up
+ * Calling {@link #setPosition(Point)} on a GraphicsGroup sets where the group’s local (0,0) shows up
  * within its parent. This means that a group’s position is not necessarily the upper left, the
  * center, or any other fixed relationship with the shapes inside the group. Instead, you determine
  * how the group’s graphics relate to the whole group’s position when you set the position of each
@@ -61,7 +61,7 @@ public GraphicsGroup() {
     public void add(GraphicsObject gObject) {
         gObject.addObserver(this);
         children.add(gObject);
-        gObject.setCanvas(getCanvas());
+        gObject.setParent(this);
         changed();
     }
 
@@ -85,7 +85,7 @@ public void add(GraphicsObject gObject, double x, double y) {
      */
     public void remove(GraphicsObject gObject) {
         gObject.removeObserver(this);
-        gObject.setCanvas(null);
+        gObject.setParent(null);
         if (!children.removeIf(child -> child == gObject)) {
             throw new NoSuchElementException("The object to remove is not part of this graphics group. Either it is already removed, or it was never originally added.");
         }
@@ -100,7 +100,7 @@ public void removeAll() {
         while (it.hasNext()) {
             GraphicsObject obj = it.next();
             obj.removeObserver(this);
-            obj.setCanvas(null);
+            obj.setParent(null);
             it.remove();
         }
         changed();
@@ -190,14 +190,6 @@ void forEachDescendant(Point origin, BiConsumer<GraphicsObject,Point> callback)
         }
     }
 
-    @Override
-    void setCanvas(CanvasWindow canvas) {
-        super.setCanvas(canvas);
-        for (GraphicsObject child : children) {
-            child.setCanvas(canvas);
-        }
-    }
-
     @Override
     protected void changed() {
         boundsNeedUpdate();

src/edu/macalester/graphics/GraphicsObject.java

@@ -20,7 +20,7 @@
  */
 public abstract class GraphicsObject {
     private final List<GraphicsObserver> observers = new ArrayList<>();
-    private CanvasWindow canvas;
+    private GraphicsGroup parent;
 
     private Point position = Point.ORIGIN;
     private double rotation = 0;
@@ -458,18 +458,27 @@ void forEachDescendant(Point origin, BiConsumer<GraphicsObject,Point> callback)
         callback.accept(this, origin.add(getPosition()));
     }
 
+    /**
+     * Returns the group that contains this graphics object, or null if it does not belong to a group.
+     */
+    public GraphicsGroup getParent() {
+        return parent;
+    }
+
     /**
      * Returns the window that this Object is inside, or null if it does not belong to a window.
      */
-    public final CanvasWindow getCanvas() {
-        return canvas;
+    public CanvasWindow getCanvas() {
+        return (parent == null) ? null : parent.getCanvas();
     }
 
-    void setCanvas(CanvasWindow canvas) {
-        if (canvas != this.canvas && canvas != null && this.canvas != null) {
-            throw new IllegalStateException("Trying to add graphics object to two different windows");
+    void setParent(GraphicsGroup parent) {
+        if (parent != this.parent && parent != null && this.parent != null) {
+            throw new IllegalStateException(
+                "Cannot add " + this.getClass().getSimpleName() + " to group,"
+                + " because it already belongs to a different group");
         }
-        this.canvas = canvas;
+        this.parent = parent;
     }
 
     /**

test/edu/macalester/graphics/CanvasWindowTest.java

@@ -79,6 +79,29 @@ void getElementAt() throws IOException {
         assertEquals(null, canvas.getElementAt(new Point(41, 51)));
     }
 
+    @Test
+    void getCanvas() {
+        GraphicsGroup g1 = new GraphicsGroup();
+        GraphicsGroup g2 = new GraphicsGroup();
+        GraphicsGroup g3 = new GraphicsGroup();
+        canvas = new CanvasWindow("getCanvas", 10, 10);
+
+        assertEquals(null, g1.getCanvas());  // Never added
+
+        g1.add(g2);
+        canvas.add(g1);
+        assertEquals(canvas, g1.getCanvas());  // Added directly
+        assertEquals(canvas, g2.getCanvas());  // Added indirectly via existing relationship
+
+        g2.add(g3);
+        assertEquals(canvas, g3.getCanvas());  // Added indirectly after parent already in canvas
+
+        g1.remove(g2);
+        assertEquals(canvas, g1.getCanvas());
+        assertEquals(null, g2.getCanvas());
+        assertEquals(null, g3.getCanvas());
+    }
+
     @Test
     void embeddedComponentHandling() throws IOException {
         canvas = new CanvasWindow("embeddedComponentHandling", 320, 60);

test/edu/macalester/graphics/GraphicsGroupTest.java

@@ -36,6 +36,26 @@ public GraphicsObject getGraphicsObject() {
         return group;
     }
 
+    @Test
+    void parentRelationships() {
+        group = new GraphicsGroup();
+        assertEquals(null, group.getParent());
+        assertEquals(null, circle.getParent());
+
+        group.add(circle);
+        assertEquals(group, circle.getParent());
+        assertEquals(null, group.getParent());
+
+        GraphicsGroup group2 = new GraphicsGroup();
+        assertThrows(IllegalStateException.class, () -> group2.add(circle));
+
+        group.remove(circle);
+        assertEquals(null, circle.getParent());
+
+        group2.add(circle);
+        assertEquals(group2, circle.getParent());
+    }
+
     @RenderingTest
     void simple() {
         group = new GraphicsGroup();