diff --git a/core/src/main/java/edu/umd/cs/piccolo/POffscreenCanvas.java b/core/src/main/java/edu/umd/cs/piccolo/POffscreenCanvas.java
index bf37269..cb8aa9b 100644
--- a/core/src/main/java/edu/umd/cs/piccolo/POffscreenCanvas.java
+++ b/core/src/main/java/edu/umd/cs/piccolo/POffscreenCanvas.java
@@ -55,12 +55,13 @@
     /** Render quality. */
     private int renderQuality = DEFAULT_RENDER_QUALITY;
 
-    /** Whether this node's background color should be drawn when rendering. */
+    /** True if this offscreen canvas is opaque. */
     private boolean opaque;
 
-    /** Background color to paint before the contents of the scene are rendered. */
+    /** Background color for this offscreen canvas. */
     private Color backgroundColor;
 
+
     /**
      * Create a new offscreen canvas the specified width and height.
      * 
@@ -81,11 +82,11 @@
         backgroundColor = null;
     }
 
+
     /**
      * Render this offscreen canvas to the specified graphics.
-     * 
-     * @param graphics graphics to render this offscreen canvas to, must not be
-     *            null
+     *
+     * @param graphics graphics to render this offscreen canvas to, must not be null
      */
     public void render(final Graphics2D graphics) {
         if (graphics == null) {
@@ -94,7 +95,7 @@
         
         if (opaque && backgroundColor != null) {
             graphics.setBackground(backgroundColor);
-            graphics.clearRect(0, 0, (int)bounds.getWidth(), (int)bounds.getHeight());
+            graphics.clearRect(0, 0, (int) bounds.getWidth(), (int) bounds.getHeight());
         }
         
         final PPaintContext paintContext = new PPaintContext(graphics);
@@ -181,27 +182,54 @@
     }
     
     /**
-     * Return the root of the scene this POffscreenCanvas is viewing.
+     * Return the root node of the scene graph for this offscreen canvas.  The
+     * root node will be null if the camera for this offscreen canvas is null.
      * 
-     * @return root element of the scene being viewed
+     * @return the root node of the scene graph for this offscreen canvas
      */
     public PRoot getRoot() {
-        return camera.getRoot();
+        return camera == null ? null : camera.getRoot();
     }
 
+    /**
+     * Return true if this offscreen canvas is opaque.  Defaults to <code>false</code>.
+     *
+     * @return true if this offscreen canvas is opaque
+     */
     public boolean isOpaque() {
         return opaque;
     }
 
-    public void setOpaque(boolean opaque) {
+    /**
+     * Set to true if this offscreen canvas is opaque.
+     *
+     * @param opaque true if this offscreen canvas is opaque
+     */
+    public void setOpaque(final boolean opaque) {
         this.opaque = opaque;
     }
 
+    /**
+     * Return the background color for this offscreen canvas.  If this
+     * offscreen canvas is opaque, the background color will be painted
+     * before the contents of the scene are rendered.
+     *
+     * @see #isOpaque
+     * @return the background color for this offscreen canvas
+     */
     public Color getBackground() {
         return backgroundColor;
     }
 
-    public void setBackground(Color backgroundColor) {
+    /**
+     * Set the background color for this offscreen canvas to <code>backgroundColor</code>.
+     * If this offscreen canvas is opaque, the background color will be painted
+     * before the contents of the scene are rendered.
+     *
+     * @see #isOpaque
+     * @param backgroundColor background color for this offscreen canvas
+     */
+    public void setBackground(final Color backgroundColor) {
         this.backgroundColor = backgroundColor;
     }
 }
\ No newline at end of file
diff --git a/core/src/test/java/edu/umd/cs/piccolo/POffscreenCanvasTest.java b/core/src/test/java/edu/umd/cs/piccolo/POffscreenCanvasTest.java
index 6f97b14..8528dd2 100644
--- a/core/src/test/java/edu/umd/cs/piccolo/POffscreenCanvasTest.java
+++ b/core/src/test/java/edu/umd/cs/piccolo/POffscreenCanvasTest.java
@@ -36,6 +36,7 @@
 import junit.framework.TestCase;
 import edu.umd.cs.piccolo.PCamera;
 import edu.umd.cs.piccolo.nodes.PPath;
+import edu.umd.cs.piccolo.util.PBounds;
 import edu.umd.cs.piccolo.util.PPaintContext;
 
 /**
@@ -104,6 +105,34 @@
         }
     }
 
+    public void testRenderEmptyOpaqueNullBackgroundColor() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        final BufferedImage image = new BufferedImage(100, 200, BufferedImage.TYPE_INT_ARGB);
+        final Graphics2D graphics = image.createGraphics();
+        canvas.setOpaque(true);
+        canvas.render(graphics);
+        for (int x = 0; x < 100; x++) {
+            for (int y = 0; y < 200; y++) {
+                assertEquals(0, image.getRGB(x, y));
+            }
+        }
+    }
+
+    public void testRenderEmptyOpaque() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        final BufferedImage image = new BufferedImage(100, 200, BufferedImage.TYPE_INT_ARGB);
+        final Graphics2D graphics = image.createGraphics();
+        canvas.setOpaque(true);
+        canvas.setBackground(Color.RED);
+        canvas.render(graphics);
+        for (int x = 0; x < 100; x++) {
+            for (int y = 0; y < 200; y++) {
+                // red pixel, RGBA is 255, 0, 0, 255
+                assertEquals(-65536, image.getRGB(x, y));
+            }
+        }
+    }
+
     public void testRenderFull() {
         final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
         final PPath rect = PPath.createRectangle(0.0f, 0.0f, 200.0f, 300.0f);
@@ -149,6 +178,12 @@
         }
     }
 
+    public void testRepaint() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        canvas.repaint(null);
+        canvas.repaint(new PBounds(0.0, 0.0, 50.0, 50.0));
+    }
+
     public void testPaintImmediately() {
         final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
         canvas.paintImmediately();
@@ -170,4 +205,29 @@
         canvas.setInteracting(true);
         canvas.setInteracting(false);
     }
+
+    public void testRoot() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        assertNotNull(canvas.getRoot());
+    }
+
+    public void testRootIsNullWhenCameraIsNull() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        canvas.setCamera(null);
+        assertEquals(null, canvas.getRoot());
+    }
+
+    public void testOpaque() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        assertFalse(canvas.isOpaque());
+        canvas.setOpaque(true);
+        assertTrue(canvas.isOpaque());
+    }
+
+    public void testBackground() {
+        final POffscreenCanvas canvas = new POffscreenCanvas(100, 200);
+        assertEquals(null, canvas.getBackground());
+        canvas.setBackground(Color.RED);
+        assertEquals(Color.RED, canvas.getBackground());
+    }
 }
\ No newline at end of file