WaylandBackend: copying to clipboard

This forwards the internal clipboard to the host, but does not handle
the primary selection nor accessing the host's clipboard internally.

The source is recreated for every new copy, rather than being reused
when it is still valid. This doesn't seem to be necessary, but doing it
differently leads to clipboard managers not becoming aware of the reused
copies (under Sway, `wl-paste --watch` doesn't notice them), which at
least suggests that not reusing is more common.

src/Backends/WaylandBackend.cpp

@@ -640,6 +640,10 @@ namespace gamescope
         void Wayland_XXColorManager_SupportedPrimariesNamed( xx_color_manager_v3 *pXXColorManager, uint32_t uPrimaries );
         static const xx_color_manager_v3_listener s_XXColorManagerListener;
 
+        void Wayland_DataSource_Send( struct wl_data_source *pSource, const char *pMime, int nFd );
+        void Wayland_DataSource_Cancelled( struct wl_data_source *pSource );
+        static const wl_data_source_listener s_DataSourceListener;
+
         CWaylandInputThread m_InputThread;
 
         CWaylandConnector m_Connector;
@@ -665,6 +669,10 @@ namespace gamescope
         wp_fractional_scale_manager_v1 *m_pFractionalScaleManager = nullptr;
         xdg_toplevel_icon_manager_v1 *m_pToplevelIconManager = nullptr;
 
+        wl_data_device_manager *m_pDataDeviceManager = nullptr;
+        wl_data_device *m_pDataDevice = nullptr;
+        std::shared_ptr<std::string> m_pClipboard = nullptr;
+
         struct 
         {
             std::vector<xx_color_manager_v3_primaries> ePrimaries;
@@ -692,6 +700,7 @@ namespace gamescope
 
         uint32_t m_uPointerEnterSerial = 0;
         bool m_bMouseEntered = false;
+        uint32_t m_uKeyboardEnterSerial = 0;
         bool m_bKeyboardEntered = false;
 
         std::shared_ptr<INestedHints::CursorInfo> m_pCursorInfo;
@@ -752,6 +761,11 @@ namespace gamescope
         .supported_tf_named        = WAYLAND_USERDATA_TO_THIS( CWaylandBackend, Wayland_XXColorManager_SupportedTFNamed ),
         .supported_primaries_named = WAYLAND_USERDATA_TO_THIS( CWaylandBackend, Wayland_XXColorManager_SupportedPrimariesNamed ),
     };
+    const wl_data_source_listener CWaylandBackend::s_DataSourceListener =
+    {
+        .send      = WAYLAND_USERDATA_TO_THIS( CWaylandBackend, Wayland_DataSource_Send ),
+        .cancelled = WAYLAND_USERDATA_TO_THIS( CWaylandBackend, Wayland_DataSource_Cancelled ),
+    };
 
     //////////////////
     // CWaylandFb
@@ -2005,7 +2019,21 @@ namespace gamescope
     }
     void CWaylandBackend::SetSelection( std::shared_ptr<std::string> szContents, GamescopeSelection eSelection )
     {
-        // Do nothing
+        if ( !m_pDataDevice )
+            m_pDataDevice = wl_data_device_manager_get_data_device( m_pDataDeviceManager, m_pSeat );
+
+        if ( eSelection == GAMESCOPE_SELECTION_CLIPBOARD && m_pDataDevice )
+        {
+            m_pClipboard = szContents;
+            wl_data_source *source = wl_data_device_manager_create_data_source( m_pDataDeviceManager );
+            wl_data_source_add_listener( source, &s_DataSourceListener, this );
+            wl_data_source_offer( source, "text/plain" );
+            wl_data_device_set_selection( m_pDataDevice, source, m_uKeyboardEnterSerial );
+        }
+        else if ( eSelection == GAMESCOPE_SELECTION_PRIMARY )
+        {
+            // Do nothing
+        }
     }
 
     std::shared_ptr<INestedHints::CursorInfo> CWaylandBackend::GetHostCursor()
@@ -2183,6 +2211,10 @@ namespace gamescope
         {
             m_pToplevelIconManager = (xdg_toplevel_icon_manager_v1 *)wl_registry_bind( pRegistry, uName, &xdg_toplevel_icon_manager_v1_interface, 1u );
         }
+        else if ( !strcmp( pInterface, wl_data_device_manager_interface.name ) )
+        {
+            m_pDataDeviceManager = (wl_data_device_manager *)wl_registry_bind( pRegistry, uName, &wl_data_device_manager_interface, 3u );
+        }
     }
 
     void CWaylandBackend::Wayland_Modifier( zwp_linux_dmabuf_v1 *pDmabuf, uint32_t uFormat, uint32_t uModifierHi, uint32_t uModifierLo )
@@ -2288,6 +2320,7 @@ namespace gamescope
         if ( !IsSurfacePlane( pSurface ) )
             return;
 
+        m_uKeyboardEnterSerial = uSerial;
         m_bKeyboardEntered = true;
 
         UpdateCursor();
@@ -2321,6 +2354,20 @@ namespace gamescope
         m_XXColorManagerFeatures.ePrimaries.push_back( static_cast<xx_color_manager_v3_primaries>( uPrimaries ) );
     }
 
+    // Data Source
+
+    void CWaylandBackend::Wayland_DataSource_Send( struct wl_data_source *pSource, const char *pMime, int nFd )
+    {
+        ssize_t len = m_pClipboard->length();
+        if ( write( nFd, m_pClipboard->c_str(), len ) != len )
+            xdg_log.infof( "Failed to write all %zd bytes to clipboard", len );
+        close( nFd );
+    }
+    void CWaylandBackend::Wayland_DataSource_Cancelled( struct wl_data_source *pSource )
+    {
+        wl_data_source_destroy( pSource );
+    }
+
     ///////////////////////
     // CWaylandInputThread
     ///////////////////////