It's not possible to get the surface damage before calling
Scene::paint(), which is a big problem because it blocks proper surface
damage and buffer damage calculation when walking render layer tree.
This change reworks the scene compositing stages to allow getting the
next surface damage before calling Scene::paint().
The main challenge is that the effects can expand the surface damage. We
have to call prePaintWindow() and prePaintScreen() before actually
starting painting. However, prePaintWindow() is called after starting
rendering.
This change makes Scene call prePaintWindow() and prePaintScreen() so
it's possible to know the surface damage beforehand. Unfortunately, it's
also a breaking change. Some fullscreen effects will have to adapt to
the new Scene paint order. Paint hooks will be invoked in the following
order:
* prePaintScreen() once per frame
* prePaintWindow() once per frame
* paintScreen() can be called multiple times
* paintWindow() can be called as many times as paintScreen()
* postPaintWindow() once per frame
* postPaintScreen() once per frame
After walking the render layer tree, the Compositor will poke the render
backend for the back buffer repair region and combine it with the
surface damage to get the buffer damage, which can be passed to the
render backend (in order to optimize performance with tiled gpus) and
Scene::paint(), which will determine what parts of the scene have to
repainted based on the buffer damage.
We already try to ensure that the surface damage is within render target
bounds. Avoid clipping surface damage in render backend, which is a bit
excessive task and perhaps it should be done an abstraction level above.
If the main surface is translucent (e.g. it contains only the drop
shadow) but its subsurface is opaque, the "window->isOpaque()" check
will produce a false positive.
Software cursor has always been a major source of problems. Hopefully,
porting it to RenderLayer will help us with that.
Note that the cursor layer is currently visible only when using software
cursor, however it will be changed once the Compositor can allocate
a real hardware cursor plane.
Currently, software cursor uses graphics-specific APIs (OpenGL and
QPainter) to paint itself. That will be changed in the future when
rendering parts are extracted from the Scene in a reusable helper.
This is the first tiny step towards the layer-based compositing in kwin.
The RenderLayer represents a layer with some contents. The actual
contents is represented by the RenderLayerDelegate class.
Currently, the RenderLayer is just a simple class responsible for
geometry, and repaints, but it will grow in the future. For example,
render layers need to form a tree.
The next (missing) biggest component in the layer-based compositing are
output layers. When output layers are added, each render layer would
have an output layer assigned to it or have its output layer inherited
from the parent.
The render layer tree wouldn't be affected by changes to the output
layer tree so transition between software and hardware cursors can be
seamless.
The next big milestone will be to try to port some of existing kwin
functionality to the RenderLayer, e.g. software cursor or screen edges.
The responsibilities of the Scene must be reduced to painting only so we
can move forward with the layer-based compositing.
This change moves direct scanout logic from the opengl scene to the base
scene class and the compositor. It makes the opengl scene less
overloaded and allows to share direct scanout logic.
paintScreen() already tries to ensure that the damage region doesn't go
outside the scene geometry. With this change, it will try to clip the
damage region to the render target rect, which saves us an extra region
intersection and simplifies code that calls paintScreen().
Having a render loop in the Platform has always been awkward. Another
way to interpret the platform not supporting per screen rendering would
be that all outputs share the same render loop.
On X11, Scene::painted_screen is going to correspond to the primary
screen, we should not rely on this assumption though!
Neither SceneQPainter nor SceneOpenGL have to compute the projection
matrix by themselves. It can be done by the Scene when setting the
projection matrix. The main benefit behind this change is that it
reduces the amount of custom setup code around paintScreen(), which
makes us one step closer to getting rid of graphics-specific paint()
function and just calling paintScreen().
Because the GLRenderTarget and the GLVertexBuffer use the global
coordinate system, they are not ergonomic in render layers.
Assigning the device pixel ratio to GLRenderTarget and GLVertexBuffer is
an interesting api design choice too. Scaling is a window system
abstraction, which is absent in OpenGL or Vulkan. For example, it's not
possible to create an OpenGL texture with a scale factor of 2. It only
works with device pixels.
This change makes the GLRenderTarget and the GLVertexBuffer more
ergonomic for usages other than rendering the workspace by removing all
the global coordinate system and scaling stuff. That's the
responsibility of the users of those two classes.
On Wayland, a window can have subsurfaces. The spec doesn't require the
main surface and its sub-surfaces to have the same scale factor.
Given that Toplevel::bufferScale() makes no sense with Wayland windows,
this change drops it to make code more reasonable and to prevent people
from using Toplevel::bufferScale().
The Compositor contains nothing that can potentially get dirty and need
repainting.
As is, the advantages of this move aren't really noticeable, but it
makes sense with multiple scenes.
Backend parts are far from ideal, they can be improved later on as we
progress with the scene redesign.
Currently, the scene owns the renderer, which puts more
responsibilities on the scene other than painting windows and it also
puts some limitations on what we can do, for example, there can be only
one scene, etc.
This change decouples the scene and the renderer so the scene is more
swappable.
Scenes are no longer implemented as plugins because opengl backend
and scene creation needs to be wrapped in opengl safety points. We
could still create the render backend and then go through the list
of scene plugins, but accessing concrete scene implementation is
much much simpler. Besides that, having scenes implemented as plugins
is not worthwhile because there are only two scenes and each contributes
very small amount of binary size. On the other hand, we still need to
take into account how many times kwin accesses the hard drive to load
plugins in order to function as expected.
This decouples the management of Shadow from the scene window and allows
multiple items share the same Shadow.
Currently, kwin has a single scene graph, but it makes sense to create a
scene graph per output as they could have different layers, etc. This
would also allow QtQuick share more textures with kwin, which is worth
doing for optimization purposes in the future.
We use surfaceless contexts with internal windows. We also require
the EGL_KHR_surfaceless_context extension for making context current
without outputs.
Arguably, we could use pbuffers, but since mainstream drivers (Mesa and
NVIDIA) support surfaceless contexts, the extra complexity doesn't buy
us anything.
This further decouples scene items from scene windows. The SurfaceItem
still needs to access the underlying window, I would like to re-iterate
over that later.
With this change, it will be possible to introduce WindowItem factory
function in the Toplevel class.
Makes it possible to apply the dpms settings per screen instead of
applying it to all of them, which is wrong at many levels.
Will be even more important with other effects like rotation.
Currently, thumbnail items are rendered by kwin. This means that qtquick
code cannot do things such as applying shader effects to window thumbnails
or simply draw custom controls on top of thumbnails.
With this change, task switchers and qml extensions will be able to
place their own contents on top of thumbnails and apply custom effects
to them.
In order to integrate window thumbnails, a window is rendered on kwin
side using its own opengl context. A fence is inserted in the command
stream to ensure that the qtquick machinery doesn't start using the
offscreen texture while there are still rendering commands being executed.
Thumbnails are rendered into offscreen textures as we don't have full
control over when qtquick windows render their contents and to work around
the fact that things such as VAOs can't be shared across OpenGL contexts.
WindowThumbnailItem and DesktopThumbnailItem act as texture providers.
At the moment, we handle window quads inefficiently. Window quads from
all items are merged into a single list just to be broken up again.
This change removes window quads from libkwineffects. This allows us to
handle window quads efficiently. Furthermore, we could optimize methods
such as WindowVertex::left() and so on. KWin spends reasonable amount
of time in those methods when many windows have to be composited.
It's a necessary prerequisite for making wl_surface painting code role
agnostic.
The scene items depend on the scene windows for caching window quads.
The goal of this change is to move window quads management to item.
Merging window quads in one list and then splitting them is inefficient,
it will be highly desirable if window quads are removed from the public
api so we can optimize window quad management.
With this change, the window quad type becomes irrelevant to render
backends for the most part. Note that the Xrender backend is a bit
nitpicky about window quads, so the shadow item doesn't create generic
"WindowQuadShadow" quads anymore.
The Xrender backend was added at the time when OpenGL drivers were not
particularly stable. Nowadays though, it's a totally different situation.
The OpenGL render backend has been the default one for many years. It's
quite stable, and it allows implementing many advanced features that
other render backends don't.
Many features are not tested with it during the development cycle; the
only time when it is noticed is when changes in other parts of kwin break
the build in the xrender backend. Effectively, the xrender backend is
unmaintained nowadays.
Given that the xrender backend is effectively unmaintained and our focus
being shifted towards wayland, this change drops the xrender backend in
favor of the opengl backend.
Besides being de-facto unmaintained, another issue is that QtQuick does
not support and most likely will never support the Xrender API. This
poses a problem as we want thumbnail items to be natively integrated in
the qtquick scene graph.
Currently, the frameRendered() signal is emitted every time an effect
calls paintScreen(). This means that the frameRendered() signal can be
emitted more than once when effects such as slide are active. However,
we'd like if it's emitted only once before buffers are swapped.
Currently, the implementation of the DecoratedClient and the decoration
renderer are strongly coupled. This poses a problem with the item based
design as the ultimate goal is to have scene items construct paint nodes
which are then fed to the renderer. The DecorationItem has to have
control over the decoration texture. Another issue is that the scene
cannot smoothly cross-fade between two window states if the decoration
is removed, e.g. from fullscreen mode to normal and vice versa.
This change moves the decoration renderer to the decoration item. With
the introduction of a generic scene texture atlas, we hope to get rid of
the decoration renderer altogether.
