Add virtual method to Scene to get the EGL/GLX extensions

Summary:
We had a few places (e.g. DebugConsole, Platform) where the Scene was
cased into a SceneOpenGL to access the backend and get the extensions.

This change simplifies that by adding a virtual method to Scene directly
which is implemented in SceneOpenGL and returns the backend's
extensions.

Thus the casts to SceneOpenGL are no longer required.

Test Plan:
Opened debug console to verify extensions are listed,
triggered Outline to verify the sharing QPA context gets created.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D7734

debug_console.cpp

@@ -22,7 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "client.h"
 #include "input_event.h"
 #include "main.h"
-#include "scene_opengl.h"
+#include "scene.h"
 #include "shell_client.h"
 #include "unmanaged.h"
 #include "wayland_server.h"
@@ -528,7 +528,7 @@ void DebugConsole::initGLTab()
     m_ui->glVersionLabel->setText(GLPlatform::versionToString(gl->glVersion()));
     m_ui->glslLabel->setText(GLPlatform::versionToString(gl->glslVersion()));
 
-    auto extensionsString = [] (const QList<QByteArray> &extensions) {
+    auto extensionsString = [] (const auto &extensions) {
         QString text = QStringLiteral("<ul>");
         for (auto extension : extensions) {
             text.append(QStringLiteral("<li>%1</li>").arg(QString::fromLocal8Bit(extension)));
@@ -537,7 +537,7 @@ void DebugConsole::initGLTab()
         return text;
     };
 
-    m_ui->platformExtensionsLabel->setText(extensionsString(static_cast<SceneOpenGL*>(Compositor::self()->scene())->backend()->extensions()));
+    m_ui->platformExtensionsLabel->setText(extensionsString(Compositor::self()->scene()->openGLPlatformInterfaceExtensions()));
     m_ui->openGLExtensionsLabel->setText(extensionsString(openGLExtensions()));
 }
 

platform.cpp

@@ -19,7 +19,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #include "platform.h"
 #include <config-kwin.h>
-#include "abstract_egl_backend.h"
 #include "composite.h"
 #include "cursor.h"
 #include "effects.h"
@@ -27,7 +26,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "overlaywindow.h"
 #include "outline.h"
 #include "pointer_input.h"
-#include "scene_opengl.h"
+#include "scene.h"
 #include "screenedge.h"
 #include "wayland_server.h"
 
@@ -353,9 +352,7 @@ void Platform::warpPointer(const QPointF &globalPos)
 bool Platform::supportsQpaContext() const
 {
     if (Compositor *c = Compositor::self()) {
-        if (SceneOpenGL *s = dynamic_cast<SceneOpenGL*>(c->scene())) {
-            return s->backend()->hasExtension(QByteArrayLiteral("EGL_KHR_surfaceless_context"));
-        }
+        return c->scene()->openGLPlatformInterfaceExtensions().contains(QByteArrayLiteral("EGL_KHR_surfaceless_context"));
     }
     return false;
 }

scene.cpp

@@ -671,6 +671,11 @@ QImage *Scene::qpainterRenderBuffer() const
     return nullptr;
 }
 
+QVector<QByteArray> Scene::openGLPlatformInterfaceExtensions() const
+{
+    return QVector<QByteArray>{};
+}
+
 //****************************************
 // Scene::Window
 //****************************************

scene.h

@@ -175,6 +175,15 @@ public:
      **/
     virtual QImage *qpainterRenderBuffer() const;
 
+    /**
+     * The backend specific extensions (e.g. EGL/GLX extensions).
+     *
+     * Not the OpenGL (ES) extension!
+     *
+     * Default implementation returns empty list
+     **/
+    virtual QVector<QByteArray> openGLPlatformInterfaceExtensions() const;
+
 Q_SIGNALS:
     void frameRendered();
 

scene_opengl.cpp

@@ -1021,6 +1021,11 @@ bool SceneOpenGL::animationsSupported() const
     return !GLPlatform::instance()->isSoftwareEmulation();
 }
 
+QVector<QByteArray> SceneOpenGL::openGLPlatformInterfaceExtensions() const
+{
+    return m_backend->extensions().toVector();
+}
+
 //****************************************
 // SceneOpenGL2
 //****************************************

scene_opengl.h

@@ -82,6 +82,8 @@ public:
         return m_backend;
     }
 
+    QVector<QByteArray> openGLPlatformInterfaceExtensions() const override;
+
     /**
      * Copy a region of pixels from the current read to the current draw buffer
      */