The main motivation behind the split is to simplify client buffer code
and allow adding new features easier, for example referencing the shm
pool when a shm buffer is destroyed, or monitoring for readable linux
dmabuf file descriptors, etc.
Also, a referenced ClientBuffer cannot be destroyed, unlike the old
BufferInterface.
If window quads need to be generated after the wl_surface is destroyed,
the SurfaceItemWayland::mapToBuffer() function will return wrong values.
In order to fix that, we need to store the last surface-to-buffer matrix
in SurfaceItem.
Xwayland windows have two geometry types that are used during rendering
- wl_surface's geometry and x11 window's geometry. Unfortunately, it's
not possible just ignore the x11 window geometry because the window may
have a custom shape region. Pixels outside the shape region can have
arbitrary values; it's not guaranteed that the area outside the shape
region will be transparent.
In some cases, the x11 window geometry can be larger than the wl_surface
rect. That breaks repaint logic as the SurfaceItemXwayland can draw
outside the bounding rect.
Specifically, this issue can be seen while resizing Steam interactively.
Another example is where a video game enters fullscreen mode. I
occasionally see that Red Dead Redemption II window leaves a ghost after
itself when it switches to fullscreen mode.
It's not a perfect solution, but on the other hand, it doesn't look like
there's a better way to handle this due to the fact that there are two
conflicting geometry sources.
According to the spec, if the wl_subsurface.place_below request is
called with the parent surface, the sub-surface must be placed below the
parent surface.
BUG: 438808
Originally, only x, y, width, and height property setters were used. A
bit later "position" and "size" helper setters were added to simplify
code in SurfaceItem sub-classes. It seems like setX(), setY(), setWidth(),
and setHeight() are unused now, so remove them.
The SurfaceItemXwayland has to re-build quads if the shape changes.
The SurfaceItemX11 doesn't need a similar fix as it already discards
quads whenever the shape region changes.
One can think that Item::scheduleRepaint() will trigger repaint of the
whole item, but it actually only schedules the next frame. If nothing
has changed on the screen, no real painting will be done unless maybe if
the rendering backend needs to repair the back buffer.
One of the scene redesign goals is to make wayland surface items
re-usable. So we have the same rendering path for drag-and-drop icons,
software cursors, and window surfaces.
The biggest issue at the moment is that window pixmaps are tightly
coupled with scene windows.
This change de-couples window pixmaps from scene windows. In order to
achieve that, some architecture changes were made.
The WindowPixmap class was replaced with the SurfacePixmap class. A
surface pixmap is created by a surface item.
Under the hood, a SurfacePixmap will create a PlatformSurfaceTexture
object, which contains all the information necessary for the renderer.
The SceneOpenGLTexture class was removed. However, the GLX and the EGL
on X11 backends still mess with GLTexture's internals.
Currently, dealing with sub-surfaces is very difficult due to the scene
design being heavily influenced by X11 requirements.
The goal of this change is to re-work scene abstractions to make improving
the wayland support easier.
The Item class is based on the QQuickItem class. My hope is that one day
we will be able to transition to QtQuick for painting scene, but in
meanwhile it makes more sense to have a minimalistic internal item class.
The WindowItem class represents a window. The SurfaceItem class represents
the contents of either an X11, or a Wayland, or an internal surface. The
DecorationItem and the ShadowItem class represent the server-side deco and
drop-shadow, respectively.
At the moment, the SurfaceItem is bound to the scene window, but the long
term plan is to break that connection so we could re-use the SurfaceItem
for things such as software cursors and drag-and-drop additional icons.
One of the responsibilities of the Item is to schedule repaints as needed.
Ideally, there shouldn't be any addRepaint() calls in the core code. The
Item class schedules repaints on geometry updates. In the future, it also
has to request an update if its opacity or visibility changes.
