[effects/thumbnailaside] Specify screen projection matrix

Summary:
The Lanczos filter is applied to thumbnails, so we need to specify screen
projection matrix in order to properly project window coordinates into
screen-space.

BUG: 407485

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D21224

effects/thumbnailaside/thumbnailaside.cpp

@@ -23,10 +23,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // KConfigSkeleton
 #include "thumbnailasideconfig.h"
 
-#include <QAction>
 #include <KGlobalAccel>
 #include <KLocalizedString>
 
+#include <QAction>
+#include <QMatrix4x4>
+
 namespace KWin
 {
 
@@ -62,9 +64,11 @@ void ThumbnailAsideEffect::paintScreen(int mask, QRegion region, ScreenPaintData
 {
     painted = QRegion();
     effects->paintScreen(mask, region, data);
+
+    const QMatrix4x4 projectionMatrix = data.projectionMatrix();
     foreach (const Data & d, windows) {
         if (painted.intersects(d.rect)) {
-            WindowPaintData data(d.window);
+            WindowPaintData data(d.window, projectionMatrix);
             data.multiplyOpacity(opacity);
             QRect region;
             setPositionTransformations(data, region, d.window, d.rect, Qt::KeepAspectRatio);