provide method to swap forground and background color

Signed-off-by: Florian Thienel <florian@thienel.org>
diff --git a/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/FakeGraphics.java b/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/FakeGraphics.java
index 6eb0c4f..8dc494a 100644
--- a/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/FakeGraphics.java
+++ b/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/FakeGraphics.java
@@ -249,6 +249,10 @@
 	}
 
 	@Override
+	public void swapColors() {
+	}
+
+	@Override
 	public FontResource setCurrentFont(final FontResource font) {
 		return null;
 	}
diff --git a/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/endtoend/TracingGraphics.java b/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/endtoend/TracingGraphics.java
index 3c433a9..80c3bd4 100644
--- a/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/endtoend/TracingGraphics.java
+++ b/org.eclipse.vex.core.tests/src/org/eclipse/vex/core/internal/layout/endtoend/TracingGraphics.java
@@ -250,6 +250,11 @@
 	}
 
 	@Override
+	public void swapColors() {
+		tracer.trace("Graphics.swapColors()");
+	}
+
+	@Override
 	public FontResource setCurrentFont(final FontResource font) {
 		tracer.trace("Graphics.setFont({0})", font);
 		final FontResource oldFont = getCurrentFont();
diff --git a/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/core/Graphics.java b/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/core/Graphics.java
index 35bdb48..f004d3e 100644
--- a/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/core/Graphics.java
+++ b/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/core/Graphics.java
@@ -88,6 +88,8 @@
 
 	public ColorResource setBackground(ColorResource color);
 
+	public void swapColors();
+
 	public FontResource setCurrentFont(FontResource font);
 
 	public void setLineStyle(LineStyle style);
diff --git a/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/widget/swt/SwtGraphics.java b/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/widget/swt/SwtGraphics.java
index 544a593..8fe81e5 100644
--- a/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/widget/swt/SwtGraphics.java
+++ b/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/widget/swt/SwtGraphics.java
@@ -282,6 +282,11 @@
 	}
 
 	@Override
+	public void swapColors() {
+		setForeground(setBackground(getForeground()));
+	}
+
+	@Override
 	public void setLineStyle(final LineStyle style) {
 		lineStyle = style;
 		switch (style) {