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+UNO-based graphics backend, lesser impedance to modern graphics APIs
+than vcl.
+
+== The Canvas Framework ==
+
+The canvas framework is the successor of the system GUI and graphics
+backend VCL. Basic functionality is available, supplying just as much
+features as necessary to provide a VCL-equivalent feature set (except
+proper BiDi/CTL support).
+
+The canvas framework consists of the following two modules, canvas and
+cppcanvas. Additionally, a new generic graphics tooling is used (but
+not exclusively by the canvas, Armin's drawinglayer module also make
+use of it), which resides in basegfx.
+
+The UNO API used by the canvas is primarily under
+css::rendering, with css::rendering::XCanvas
+being the central interface.
+
+== The slideshow engine ==
+
+The slideshow engine has replaced the former Impress-embedded
+presentation framework with a fully independent UNO component, and it
+is based on the canvas. Some features used there are only available
+from canvas, like double-buffering, and hardware-accelerated
+alpha-blending (currently not on all platforms).
+
+== Cairo canvas ==
+
+cairo canvas is one of backends of canvas component. canvas is mostly
+used for slideshow rendering and also for emf+ rendering. we hoped it
+will even be used by drawing layer, but it didn't happen (yet?) for
+API look at offapi/com/sun/star/rendering/, the implementation is in
+canvas and cppcanvas modules.
+
+cairo canvas backend uses cairo library for rendering. main advantage
+is support of alpha transparency and in some cases accelerated
+rendering.
+
+the backend itself is quite old and stable, not many changes in that
+area lately, mostly changes for emf+ rendering, communication with
+vcl and bugfixes
+
+FUTURE work: look at cairo canvas and situation when it is used
+(mostly slideshow). TODO there still might be more cases when we
+can save some roundtrips when exchanging data with vcl.