Merge branch 'master' into windows+cc

[ardour.git] / libs / canvas / canvas / item.h

diff --git a/libs/canvas/canvas/item.h b/libs/canvas/canvas/item.h
index b4ea5671c7fe6d499ec0a3d10668bcc304518d35..e856c7e149c18a9a28ce013e4d47a1f634eff3d5 100644 (file)
--- a/libs/canvas/canvas/item.h
+++ b/libs/canvas/canvas/item.h
@@ -57,7 +57,15 @@ public:
        virtual ~Item ();
 
        /** Render this item to a Cairo context.
-        *  @param area Area to draw in this item's coordinates.
+        *  @param area Area to draw, in **window** coordinates
+        *
+        *  Items must convert their own coordinates into window coordinates
+        *  because Cairo is limited to a fixed point coordinate space that
+        *  does not extend as far as the Ardour timeline. All rendering must
+        *  be done using coordinates that do not exceed the (rough) limits
+        *  of the canvas' window, to avoid odd errors within Cairo as it
+        *  converts doubles into its fixed point format and then tesselates
+        *  the results.
         */
        virtual void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const = 0;
 
@@ -105,8 +113,13 @@ public:
         Duple canvas_to_item (Duple const &) const;
        void item_to_canvas (Coord &, Coord &) const;
        Rect item_to_canvas (Rect const &) const;
+       Rect canvas_to_item (Rect const &) const;
         Duple item_to_canvas (Duple const &) const;
 
+        Duple item_to_window (Duple const&) const;
+        Duple window_to_item (Duple const&) const;
+        Rect item_to_window (Rect const&) const;
+
        void raise_to_top ();
        void raise (int);
        void lower_to_bottom ();