GLRenderTarget doesn't provide a generic abstraction for framebuffer
objects, so let's call GLRenderTarget what it is - a framebuffer.
Renaming the GLRenderTarget class allows us to use the term "render
target" which abstracts fbos or shm images without creating confusion.
This allows us to make the GLRenderTarget a bit nicer when using it to
wrap the default fbo as we don't know what the color attachment texture
is besides its size.
This means that the responsibility of ensuring that the color attachment
outlives the fbo is now up to the caller. However, most of kwin code
has been written that way, so it's not an issue.
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.
