Adding upstream version 4:7.4.7.upstream/4%7.4.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+# UNO-based Graphics Backend
+
+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 Works
+
+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.