--- a/gtk/canvas.d	Wed Jul 15 23:49:02 2009 +0930
+++ b/gtk/canvas.d	Thu Jul 16 00:12:02 2009 +0930
@@ -122,7 +122,7 @@
                0, 0);
     }
 
-    override void zoom_relative(Point pixel_datum, double factor) {
+    override void zoom_relative(in Point pixel_datum, in double factor) {
         // Work out pixel distance from current centre to datum,
         // Do the zoom, then work out the new centre that keeps the
         // pixel distance the same
@@ -137,7 +137,7 @@
         queueDraw;
     }
 
-    override void pan_relative(Vector pixel_displacement) {
+    override void pan_relative(in Vector pixel_displacement) {
         mViewCentre = mViewCentre + pixel_to_model(pixel_displacement);
 
         update_adjustments;
@@ -145,11 +145,11 @@
         queueDraw;
     }
 
-    override void damage_model(Rectangle area) {
+    override void damage_model(in Rectangle area) {
         mDamage = mDamage | model_to_pixel(area);
     }
 
-    override void damage_pixel(Rectangle area) {
+    override void damage_pixel(in Rectangle area) {
         mDamage = mDamage | area;
     }
 
@@ -157,35 +157,35 @@
         return mZoom;
     }
 
-    override Point model_to_pixel(Point model) const {
+    override Point model_to_pixel(in Point model) const {
         return Point.DEFAULT + mViewSize / 2.0 + mZoom * (model - mViewCentre);
     }
 
-    override Point pixel_to_model(Point pixel) const {
+    override Point pixel_to_model(in Point pixel) const {
         return mViewCentre + (pixel - mViewSize / 2.0 - Point.DEFAULT) / mZoom;
     }
 
-    override Vector model_to_pixel(Vector model) const {
+    override Vector model_to_pixel(in Vector model) const {
         return mZoom * model;
     }
 
-    override Vector pixel_to_model(Vector pixel) const {
+    override Vector pixel_to_model(in Vector pixel) const {
         return pixel / mZoom;
     }
 
-    override double model_to_pixel(double model) const {
+    override double model_to_pixel(in double model) const {
         return mZoom * model;
     }
 
-    override double pixel_to_model(double pixel) const {
+    override double pixel_to_model(in double pixel) const {
         return pixel / mZoom;
     }
 
-    override Rectangle model_to_pixel(Rectangle model) const {
+    override Rectangle model_to_pixel(in Rectangle model) const {
         return Rectangle(model_to_pixel(model.position), model_to_pixel(model.size));
     }
 
-    override Rectangle pixel_to_model(Rectangle model) const {
+    override Rectangle pixel_to_model(in Rectangle model) const {
         return Rectangle(pixel_to_model(model.position), pixel_to_model(model.size));
     }
 
@@ -443,16 +443,15 @@
         }
 
         void update_rulers() {
-            Vector model_size = pixel_to_model(mViewSize);
+            invariant Vector model_size = pixel_to_model(mViewSize);
 
-            Point view_left_bottom = mViewCentre - model_size / 2.0;
-            Point view_right_top = mViewCentre + model_size / 2.0;
+            invariant Point view_left_bottom = mViewCentre - model_size / 2.0;
+            invariant Point view_right_top = mViewCentre + model_size / 2.0;
 
             // Define these just to obtain the position
             // below and we can preserve it
             double lower, upper, position, max_size;
 
-
             mHRuler.getRange(lower, upper, position, max_size);
             mHRuler.setRange(view_left_bottom.x,
                              view_right_top.x,
@@ -467,10 +466,10 @@
         }
 
         void update_adjustments() {
-            Vector model_size = pixel_to_model(mViewSize);
+            invariant Vector model_size = pixel_to_model(mViewSize);
 
-            Point view_left_bottom = mViewCentre - model_size / 2.0;
-            Point view_right_top = mViewCentre + model_size / 2.0;
+            invariant Point view_left_bottom = mViewCentre - model_size / 2.0;
+            invariant Point view_right_top = mViewCentre + model_size / 2.0;
 
             // Adjust the canvas size if necessary
             mCanvasBounds = Rectangle(min_extents(mCanvasBounds.min_corner, view_left_bottom),
@@ -507,7 +506,7 @@
                 int x, y, w, h;
                 mDamage.get_quantised(x, y, w, h);
                 //writefln("Quantised damage: %d %d %d %d", x, y, w, h);
-                y = cast(int)mViewSize.y - (y + h);
+                y = cast(int)mViewSize.y - (y + h);         // Flip vertical axis
                 //writefln("Flipped Quantised damage: %d %d %d %d", x, y, w, h);
                 mDrawingArea.queueDrawArea(x, y, w, h);
                 //mDrawingArea.queueDraw();
@@ -518,7 +517,7 @@
             }
         }
 
-        double clamp_zoom(double zoom) { return clamp(zoom, 0.2, 10.0); }
+        double clamp_zoom(in double zoom) { return clamp(zoom, 0.2, 10.0); }
 
         bool mHadConfigure;
         Rectangle mDamage;          // pixels