Stephan Bergmann
8a734ba928
...which appears to have become even less relevant withdb89f53c31"remove OpenGL VCL backend code". And the vcl/unx/glxtest.cxx machinery that it is based on is (a) known to cause issues like <https://gitlab.freedesktop.org/mesa/mesa/-/issues/3957> "LibreOffice's OpenGL version detection code hangs when running inside a flatpak container with a different mesa version", and (b) is one of the two reasons why an soffice that uses Wayland nevertheless also requires Xwayland during startup (the other reason being oosplash). So getting rid of the glxtest machinery is beneficial. The remaining two potential uses of OpenGL on X11/Wayland are the obscure css.rendering.SpriteCanvas.OGL service implementation (about whichdb89f53c31states that "it seems has never been finished or enabled (or so it most probably should be dumped too)") and some slideshow transitions. About the latter, Caolán stated on IRC: "I think we grew this set of stuff to check for dodgy opengl primarily for the case where vcl used opengl for ordinary UI optimizations; but I think that use is gone now so I wonder does it make sense to just drop all of that entirely; for just slide transitions we apparently survived fine without the denylist for ages". (And in any case there is still the WatchdogThread support with OpenGLZone::hardDisable in VCLExceptionSignal_impl, vcl/source/app/svmain.cxx, should any OpenGL code run into problems.) (The removal of gb_LinkTarget_use_glxtest from gb_LinkTarget_use_vclmain, which indirectly brought in gb_LinkTarget_use_libraries,*,vcl, revealed that an explicit use of vcl was missing from various Executables etc., which thus had to be added now.) Change-Id: Ifa5220fd09910a4459ca546d9655e479a2e38f1e Reviewed-on: https://gerrit.libreoffice.org/c/core/+/131943 Tested-by: Jenkins Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
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.