From c6be2b51a935b15f84ed9187db98effbfc52fcef Mon Sep 17 00:00:00 2001
From: Xaver Hugl <xaver.hugl@gmail.com>
Date: Tue, 13 Feb 2024 16:29:48 +0100
Subject: [PATCH] backends/wayland: support direct scanout

This allows for (mostly) overhead-less pass-through of fullscreen content
to the host compositor
---
 src/backends/wayland/wayland_egl_backend.cpp | 25 +++++++++++++++++---
 src/backends/wayland/wayland_egl_backend.h   |  4 ++++
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/backends/wayland/wayland_egl_backend.cpp b/src/backends/wayland/wayland_egl_backend.cpp
index 0f75f024ea..11cd60168d 100644
--- a/src/backends/wayland/wayland_egl_backend.cpp
+++ b/src/backends/wayland/wayland_egl_backend.cpp
@@ -14,6 +14,8 @@
 #include "opengl/glrendertimequery.h"
 #include "opengl/glutils.h"
 #include "platformsupport/scenes/opengl/basiceglsurfacetexture_wayland.h"
+#include "scene/surfaceitem_wayland.h"
+#include "wayland/surface.h"
 #include "wayland_backend.h"
 #include "wayland_display.h"
 #include "wayland_logging.h"
@@ -109,17 +111,34 @@ bool WaylandEglPrimaryLayer::endFrame(const QRegion &renderedRegion, const QRegi
     return true;
 }
 
+bool WaylandEglPrimaryLayer::scanout(SurfaceItem *surfaceItem)
+{
+    Q_ASSERT(!m_presentationBuffer);
+    if (surfaceItem->size() != m_waylandOutput->modeSize()) {
+        return false;
+    }
+    SurfaceItemWayland *item = qobject_cast<SurfaceItemWayland *>(surfaceItem);
+    if (!item || !item->surface() || item->surface()->bufferTransform() != OutputTransform::Kind::Normal) {
+        return false;
+    }
+    m_presentationBuffer = m_backend->backend()->importBuffer(item->surface()->buffer());
+    return m_presentationBuffer;
+}
+
 void WaylandEglPrimaryLayer::present()
 {
-    wl_buffer *buffer = m_backend->backend()->importBuffer(m_buffer->buffer());
-    Q_ASSERT(buffer);
+    if (!m_presentationBuffer) {
+        m_presentationBuffer = m_backend->backend()->importBuffer(m_buffer->buffer());
+        Q_ASSERT(m_presentationBuffer);
+    }
 
     KWayland::Client::Surface *surface = m_waylandOutput->surface();
-    surface->attachBuffer(buffer);
+    surface->attachBuffer(m_presentationBuffer);
     surface->damage(m_damageJournal.lastDamage());
     surface->setScale(std::ceil(m_waylandOutput->scale()));
     surface->commit();
     Q_EMIT m_waylandOutput->outputChange(m_damageJournal.lastDamage());
+    m_presentationBuffer = nullptr;
 
     m_swapchain->release(m_buffer);
 }
diff --git a/src/backends/wayland/wayland_egl_backend.h b/src/backends/wayland/wayland_egl_backend.h
index c4da34c46e..3a7bdac382 100644
--- a/src/backends/wayland/wayland_egl_backend.h
+++ b/src/backends/wayland/wayland_egl_backend.h
@@ -15,6 +15,8 @@
 
 #include <memory>
 
+struct wl_buffer;
+
 namespace KWin
 {
 class EglSwapchainSlot;
@@ -42,6 +44,7 @@ public:
     std::optional<OutputLayerBeginFrameInfo> beginFrame() override;
     bool endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion) override;
     std::chrono::nanoseconds queryRenderTime() const override;
+    bool scanout(SurfaceItem *surfaceItem) override;
 
 private:
     WaylandOutput *m_waylandOutput;
@@ -50,6 +53,7 @@ private:
     std::shared_ptr<EglSwapchainSlot> m_buffer;
     std::unique_ptr<GLRenderTimeQuery> m_query;
     WaylandEglBackend *const m_backend;
+    wl_buffer *m_presentationBuffer = nullptr;
 
     friend class WaylandEglBackend;
 };