Currently, when screencasting a window, kwin may render a window into a
temporary offscreen texture, copy that offscreen texture to the dma-buf
render target, and discard the offscreen texture.
Allocating and deallocating offscreen textures is inefficient. Another
issue is that the screencast plugin uses Scene::Window::windowTexture().
It's a blocker for killing scene windows.
This change introduces a base ScreenCastSource type. It allows us to
move away from Scene::Window::windowTexture() and make the dma-buf code
path efficient with applications such as Firefox that utilize
sub-surfaces.
With the ScreenCastSource, kwin can also provide screen cast frames with
arbitrary device pixel ratio.
Once in a while, we receive complaints from other fellow KDE developers
about the file organization of kwin. This change addresses some of those
complaints by moving all of source code in a separate directory, src/,
thus making the project structure more traditional. Things such as tests
are kept in their own toplevel directories.
This change may wreak havoc on merge requests that add new files to kwin,
but if a patch modifies an already existing file, git should be smart
enough to figure out that the file has been relocated.
We may potentially split the src/ directory further to make navigating
the source code easier, but hopefully this is good enough already.
