Add virtual Scene::scenePainter method

Summary:
So far EffectsHandlerImpl directly accessed SceneQPainter::painter
through a dynamic cast. If in future the QPainter based compositor should
be moved into a plugin we cannot access it through a dynamic cast.

To solve this problem the painter method is moved into Scene as
a virtual method returning a sane default value.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D7214

effects.cpp

@@ -32,7 +32,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "group.h"
 #include "osd.h"
 #include "pointer_input.h"
-#include "scene_qpainter.h"
 #include "unmanaged.h"
 #ifdef KWIN_BUILD_TABBOX
 #include "tabbox.h"
@@ -1328,11 +1327,7 @@ unsigned long EffectsHandlerImpl::xrenderBufferPicture()
 
 QPainter *EffectsHandlerImpl::scenePainter()
 {
-    if (SceneQPainter *s = dynamic_cast<SceneQPainter*>(m_scene)) {
+    return m_scene->scenePainter();
-        return s->painter();
-    } else {
-        return NULL;
-    }
 }
 
 void EffectsHandlerImpl::toggleEffect(const QString& name)

scene.cpp

@@ -657,6 +657,11 @@ xcb_render_picture_t Scene::xrenderBufferPicture() const
     return XCB_RENDER_PICTURE_NONE;
 }
 
+QPainter *Scene::scenePainter() const
+{
+    return nullptr;
+}
+
 //****************************************
 // Scene::Window
 //****************************************

scene.h

@@ -163,6 +163,12 @@ public:
      **/
     virtual xcb_render_picture_t xrenderBufferPicture() const;
 
+    /**
+     * The QPainter used by a QPainter based compositor scene.
+     * Default implementation returns @c nullptr;
+     **/
+    virtual QPainter *scenePainter() const;
+
 Q_SIGNALS:
     void frameRendered();
 

scene_qpainter.cpp

@@ -281,7 +281,7 @@ void SceneQPainter::Window::performPaint(int mask, QRegion region, WindowPaintDa
         toplevel->resetDamage();
     }
 
-    QPainter *scenePainter = m_scene->painter();
+    QPainter *scenePainter = m_scene->scenePainter();
     QPainter *painter = scenePainter;
     painter->save();
     painter->setClipRegion(region);
@@ -523,7 +523,7 @@ void QPainterEffectFrame::render(QRegion region, double opacity, double frameOpa
     if (m_effectFrame->geometry().isEmpty()) {
         return; // Nothing to display
     }
-    QPainter *painter = m_scene->painter();
+    QPainter *painter = m_scene->scenePainter();
 
 
     // Render the actual frame

scene_qpainter.h

@@ -123,7 +123,7 @@ public:
         return false;
     }
 
-    QPainter *painter();
+    QPainter *scenePainter() const override;
 
     QPainterBackend *backend() const {
         return m_backend.data();
@@ -252,7 +252,7 @@ OverlayWindow* SceneQPainter::overlayWindow()
 }
 
 inline
-QPainter* SceneQPainter::painter()
+QPainter* SceneQPainter::scenePainter() const
 {
     return m_painter.data();
 }