Add hasSwapEvent getter

Summary:
Add a small getter to query information internally if the backend supports
swap events. Defaults to true as it is the default in the GBM Wayland backend.

Test Plan: i915

Reviewers: #kwin

Subscribers: kwin

Tags: #kwin

Maniphest Tasks: T11071

Differential Revision: https://phabricator.kde.org/D25298

platformsupport/scenes/opengl/backend.h

@@ -85,6 +85,7 @@ public:
     virtual bool makeCurrent() = 0;
     virtual void doneCurrent() = 0;
     virtual bool usesOverlayWindow() const = 0;
+    virtual bool hasSwapEvent() const { return true; }
     /**
      * Whether the rendering needs to be split per screen.
      * Default implementation returns @c false.

plugins/platforms/x11/standalone/glxbackend.cpp

@@ -206,11 +206,10 @@ void GlxBackend::init()
     m_haveMESACopySubBuffer = hasExtension(QByteArrayLiteral("GLX_MESA_copy_sub_buffer"));
     m_haveMESASwapControl   = hasExtension(QByteArrayLiteral("GLX_MESA_swap_control"));
     m_haveEXTSwapControl    = hasExtension(QByteArrayLiteral("GLX_EXT_swap_control"));
-    // only enable Intel swap event if env variable is set, see BUG 342582
-    m_haveINTELSwapEvent    = hasExtension(QByteArrayLiteral("GLX_INTEL_swap_event"))
-                                && qgetenv("KWIN_USE_INTEL_SWAP_EVENT") == QByteArrayLiteral("1");
 
-    if (m_haveINTELSwapEvent) {
+    // only enable Intel swap event if env variable is set, see BUG 342582
+    if (hasExtension(QByteArrayLiteral("GLX_INTEL_swap_event")) &&
+            qgetenv("KWIN_USE_INTEL_SWAP_EVENT") == QByteArrayLiteral("1")) {
         m_swapEventFilter = std::make_unique<SwapEventFilter>(window, glxWindow);
         glXSelectEvent(display(), glxWindow, GLX_BUFFER_SWAP_COMPLETE_INTEL_MASK);
     }
@@ -668,8 +667,9 @@ void GlxBackend::present()
     const bool fullRepaint = supportsBufferAge() || (lastDamage() == displayRegion);
 
     if (fullRepaint) {
-        if (m_haveINTELSwapEvent)
+        if (hasSwapEvent()) {
             Compositor::self()->aboutToSwapBuffers();
+        }
 
         glXSwapBuffers(display(), glxWindow);
 
@@ -782,6 +782,11 @@ bool GlxBackend::usesOverlayWindow() const
     return true;
 }
 
+bool GlxBackend::hasSwapEvent() const
+{
+    return m_swapEventFilter != nullptr;
+}
+
 /********************************************************
  * GlxTexture
  *******************************************************/

plugins/platforms/x11/standalone/glxbackend.h

@@ -77,6 +77,7 @@ public:
     void doneCurrent() override;
     OverlayWindow* overlayWindow() const override;
     bool usesOverlayWindow() const override;
+    bool hasSwapEvent() const override;
     void init() override;
 
 protected:
@@ -111,7 +112,6 @@ private:
     bool m_haveMESACopySubBuffer = false;
     bool m_haveMESASwapControl = false;
     bool m_haveEXTSwapControl = false;
-    bool m_haveINTELSwapEvent = false;
     Display *m_x11Display;
     friend class GlxTexture;
 };

plugins/scenes/opengl/scene_opengl.cpp

@@ -522,6 +522,11 @@ OverlayWindow *SceneOpenGL::overlayWindow() const
     return m_backend->overlayWindow();
 }
 
+bool SceneOpenGL::hasSwapEvent() const
+{
+    return m_backend->hasSwapEvent();
+}
+
 void SceneOpenGL::idle()
 {
     m_backend->idle();

plugins/scenes/opengl/scene_opengl.h

@@ -53,6 +53,7 @@ public:
     void screenGeometryChanged(const QSize &size) override;
     OverlayWindow *overlayWindow() const override;
     bool usesOverlayWindow() const override;
+    bool hasSwapEvent() const override;
     bool makeOpenGLContextCurrent() override;
     void doneOpenGLContextCurrent() override;
     Decoration::Renderer *createDecorationRenderer(Decoration::DecoratedClientImpl *impl) override;

scene.cpp

@@ -629,6 +629,11 @@ void Scene::screenGeometryChanged(const QSize &size)
     overlayWindow()->resize(size);
 }
 
+bool Scene::hasSwapEvent() const
+{
+    return false;
+}
+
 bool Scene::makeOpenGLContextCurrent()
 {
     return false;

scene.h

@@ -146,6 +146,7 @@ public:
     // there's nothing to paint (adjust time_diff later)
     virtual void idle();
     virtual OverlayWindow* overlayWindow() const = 0;
+    virtual bool hasSwapEvent() const;
 
     virtual bool makeOpenGLContextCurrent();
     virtual void doneOpenGLContextCurrent();