wayland: Implement wl_surface.preferred_buffer_scale and wl_surface.preferred_buffer_transform

The new events provide a way to tell the client what buffer scale and
buffer transform to use as they may lack the context to make a proper
decision.

CMakeLists.txt

@@ -186,7 +186,7 @@ int main() {
     mmap(nullptr, size, PROT_WRITE, MAP_SHARED, fd, 0);
 }" HAVE_MEMFD)
 
-find_package(Wayland 1.21)
+find_package(Wayland 1.22)
 set_package_properties(Wayland PROPERTIES
     TYPE REQUIRED
     PURPOSE "Required for building KWin with Wayland support"

src/wayland/compositor_interface.cpp

@@ -13,7 +13,7 @@
 
 namespace KWaylandServer
 {
-static const int s_version = 5;
+static const int s_version = 6;
 
 class CompositorInterfacePrivate : public QtWaylandServer::wl_compositor
 {

src/wayland/surface_interface.cpp

@@ -74,6 +74,7 @@ void SurfaceInterfacePrivate::addChild(SubSurfaceInterface *child)
     current.above.append(child);
     child->surface()->setOutputs(outputs);
     child->surface()->setPreferredBufferScale(preferredBufferScale);
+    child->surface()->setPreferredBufferTransform(preferredBufferTransform);
 
     Q_EMIT q->childSubSurfaceAdded(child);
     Q_EMIT q->childSubSurfacesChanged();
@@ -1119,6 +1120,10 @@ void SurfaceInterface::setPreferredBufferScale(qreal scale)
     if (d->fractionalScaleExtension) {
         d->fractionalScaleExtension->setPreferredScale(scale);
     }
+    if (d->resource()->version() >= WL_SURFACE_PREFERRED_BUFFER_SCALE_SINCE_VERSION) {
+        d->send_preferred_buffer_scale(std::ceil(scale));
+    }
+
     for (auto child : qAsConst(d->current.below)) {
         child->surface()->setPreferredBufferScale(scale);
     }
@@ -1127,4 +1132,23 @@ void SurfaceInterface::setPreferredBufferScale(qreal scale)
     }
 }
 
+void SurfaceInterface::setPreferredBufferTransform(KWin::Output::Transform transform)
+{
+    if (transform == d->preferredBufferTransform) {
+        return;
+    }
+    d->preferredBufferTransform = transform;
+
+    if (d->resource()->version() >= WL_SURFACE_PREFERRED_BUFFER_TRANSFORM_SINCE_VERSION) {
+        d->send_preferred_buffer_transform(uint32_t(transform));
+    }
+
+    for (auto child : qAsConst(d->current.below)) {
+        child->surface()->setPreferredBufferTransform(transform);
+    }
+    for (auto child : qAsConst(d->current.above)) {
+        child->surface()->setPreferredBufferTransform(transform);
+    }
+}
+
 } // namespace KWaylandServer

src/wayland/surface_interface.h

@@ -359,6 +359,14 @@ public:
      */
     void setPreferredBufferScale(qreal scale);
 
+    /**
+     * Sets the preferred buffer transform for this surface.
+     *
+     * This indicates to the client the preferred buffer transform to use when
+     * attaching buffers to this surface.
+     */
+    void setPreferredBufferTransform(KWin::Output::Transform transform);
+
 Q_SIGNALS:
     /**
      * This signal is emitted when the underlying wl_surface resource is about to be freed.

src/wayland/surface_interface_p.h

@@ -133,6 +133,7 @@ public:
 
     QVector<OutputInterface *> outputs;
     qreal preferredBufferScale = 1.0;
+    KWin::Output::Transform preferredBufferTransform = KWin::Output::Transform::Normal;
 
     LockedPointerV1Interface *lockedPointer = nullptr;
     ConfinedPointerV1Interface *confinedPointer = nullptr;

src/waylandwindow.cpp

@@ -161,6 +161,7 @@ void WaylandWindow::updateClientOutputs()
     surface()->setOutputs(waylandServer()->display()->outputsIntersecting(frameGeometry().toAlignedRect()));
     if (output()) {
         surface()->setPreferredBufferScale(output()->scale());
+        surface()->setPreferredBufferTransform(output()->transform());
     }
 }