Noel Grandin
704f61b1bd
These were originally created to better support alpha/transparency in slideshows, but vcl can do that these days. Mostly, removing these makes the path to better backends (e.g. GDI+) in vcl considerably easier. If regressions are detected, it would be better to improve vcl to perform better, or render better, since that will both fix the regression and improve other output from LibreOffice. Also remove various bits of vcl backend that were only being used by the canvas stuff. Change-Id: Ic5276d57e696f3dcbeaed2cc149b8fc09c5816f6 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/181843 Tested-by: Jenkins Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
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.