diff --git a/src/effect/effect.cpp b/src/effect/effect.cpp
index 9d903b72a1..2f6b1313cb 100644
--- a/src/effect/effect.cpp
+++ b/src/effect/effect.cpp
@@ -215,19 +215,12 @@ public:
     qreal brightness;
     int screen;
     qreal crossFadeProgress;
-    QMatrix4x4 projectionMatrix;
 };
 
 WindowPaintData::WindowPaintData()
-    : WindowPaintData(QMatrix4x4())
-{
-}
-
-WindowPaintData::WindowPaintData(const QMatrix4x4 &projectionMatrix)
     : PaintData()
     , d(std::make_unique<WindowPaintDataPrivate>())
 {
-    setProjectionMatrix(projectionMatrix);
     setOpacity(1.0);
     setSaturation(1.0);
     setBrightness(1.0);
@@ -251,7 +244,6 @@ WindowPaintData::WindowPaintData(const WindowPaintData &other)
     setBrightness(other.brightness());
     setScreen(other.screen());
     setCrossFadeProgress(other.crossFadeProgress());
-    setProjectionMatrix(other.projectionMatrix());
 }
 
 WindowPaintData::~WindowPaintData() = default;
@@ -324,21 +316,6 @@ qreal WindowPaintData::multiplyBrightness(qreal factor)
     return d->brightness;
 }
 
-void WindowPaintData::setProjectionMatrix(const QMatrix4x4 &matrix)
-{
-    d->projectionMatrix = matrix;
-}
-
-QMatrix4x4 WindowPaintData::projectionMatrix() const
-{
-    return d->projectionMatrix;
-}
-
-QMatrix4x4 &WindowPaintData::rprojectionMatrix()
-{
-    return d->projectionMatrix;
-}
-
 WindowPaintData &WindowPaintData::operator*=(qreal scale)
 {
     this->setXScale(this->xScale() * scale);
diff --git a/src/effect/effect.h b/src/effect/effect.h
index 777a2a149d..378eb8f0e1 100644
--- a/src/effect/effect.h
+++ b/src/effect/effect.h
@@ -300,7 +300,6 @@ class KWIN_EXPORT WindowPaintData : public PaintData
 {
 public:
     WindowPaintData();
-    explicit WindowPaintData(const QMatrix4x4 &projectionMatrix);
     WindowPaintData(const WindowPaintData &other);
     ~WindowPaintData() override;
     /**
@@ -437,23 +436,6 @@ public:
      */
     qreal crossFadeProgress() const;
 
-    /**
-     * Sets the projection matrix that will be used when painting the window.
-     *
-     * The default projection matrix can be overridden by setting this matrix
-     */
-    void setProjectionMatrix(const QMatrix4x4 &matrix);
-
-    /**
-     * Returns the current projection matrix.
-     */
-    QMatrix4x4 projectionMatrix() const;
-
-    /**
-     * Returns a reference to the projection matrix.
-     */
-    QMatrix4x4 &rprojectionMatrix();
-
 private:
     const std::unique_ptr<WindowPaintDataPrivate> d;
 };
diff --git a/src/effect/offscreeneffect.cpp b/src/effect/offscreeneffect.cpp
index c24c88c430..873b9e7fd6 100644
--- a/src/effect/offscreeneffect.cpp
+++ b/src/effect/offscreeneffect.cpp
@@ -117,14 +117,8 @@ void OffscreenData::maybeRender(EffectWindow *window)
         glClearColor(0.0, 0.0, 0.0, 0.0);
         glClear(GL_COLOR_BUFFER_BIT);
 
-        QMatrix4x4 projectionMatrix;
-        projectionMatrix.ortho(QRectF(0, 0, textureSize.width(), textureSize.height()));
-
         WindowPaintData data;
-        data.setXTranslation(-logicalGeometry.x());
-        data.setYTranslation(-logicalGeometry.y());
         data.setOpacity(1.0);
-        data.setProjectionMatrix(projectionMatrix);
 
         const int mask = Effect::PAINT_WINDOW_TRANSFORMED | Effect::PAINT_WINDOW_TRANSLUCENT;
         effects->drawWindow(renderTarget, viewport, window, mask, infiniteRegion(), data);
@@ -185,7 +179,7 @@ void OffscreenData::paint(const RenderTarget &renderTarget, const RenderViewport
     const qreal rgb = data.brightness() * data.opacity();
     const qreal a = data.opacity();
 
-    QMatrix4x4 mvp = data.projectionMatrix();
+    QMatrix4x4 mvp = viewport.projectionMatrix();
     mvp.translate(std::round(window->x() * scale), std::round(window->y() * scale));
 
     const auto toXYZ = renderTarget.colorDescription().colorimetry().toXYZ();
diff --git a/src/plugins/backgroundcontrast/contrast.cpp b/src/plugins/backgroundcontrast/contrast.cpp
index 56c1f92426..409f033472 100644
--- a/src/plugins/backgroundcontrast/contrast.cpp
+++ b/src/plugins/backgroundcontrast/contrast.cpp
@@ -422,7 +422,7 @@ void ContrastEffect::drawWindow(const RenderTarget &renderTarget, const RenderVi
 
         const QRegion effectiveShape = shape & region & screen;
         if (!effectiveShape.isEmpty()) {
-            doContrast(renderTarget, viewport, w, effectiveShape, w->opacity() * data.opacity(), data.projectionMatrix());
+            doContrast(renderTarget, viewport, w, effectiveShape, w->opacity() * data.opacity(), viewport.projectionMatrix());
         }
     }
 
diff --git a/src/plugins/blur/blur.cpp b/src/plugins/blur/blur.cpp
index e5feee0bb5..a29e4710f0 100644
--- a/src/plugins/blur/blur.cpp
+++ b/src/plugins/blur/blur.cpp
@@ -774,7 +774,7 @@ void BlurEffect::blur(const RenderTarget &renderTarget, const RenderViewport &vi
         GLFramebuffer::popFramebuffer();
         const auto &read = renderInfo.framebuffers[1];
 
-        projectionMatrix = data.projectionMatrix();
+        projectionMatrix = viewport.projectionMatrix();
         projectionMatrix.translate(deviceBackgroundRect.x(), deviceBackgroundRect.y());
         m_upsamplePass.shader->setUniform(m_upsamplePass.mvpMatrixLocation, projectionMatrix);
 
@@ -816,7 +816,7 @@ void BlurEffect::blur(const RenderTarget &renderTarget, const RenderViewport &vi
         if (GLTexture *noiseTexture = ensureNoiseTexture()) {
             ShaderManager::instance()->pushShader(m_noisePass.shader.get());
 
-            QMatrix4x4 projectionMatrix = data.projectionMatrix();
+            QMatrix4x4 projectionMatrix = viewport.projectionMatrix();
             projectionMatrix.translate(deviceBackgroundRect.x(), deviceBackgroundRect.y());
 
             m_noisePass.shader->setUniform(m_noisePass.mvpMatrixLocation, projectionMatrix);
diff --git a/src/plugins/screencast/windowscreencastsource.cpp b/src/plugins/screencast/windowscreencastsource.cpp
index f3acbeb9ba..7679f9580c 100644
--- a/src/plugins/screencast/windowscreencastsource.cpp
+++ b/src/plugins/screencast/windowscreencastsource.cpp
@@ -64,13 +64,10 @@ void WindowScreenCastSource::render(GLFramebuffer *target)
     RenderTarget renderTarget(target);
     RenderViewport viewport(m_window->clientGeometry(), 1, renderTarget);
 
-    WindowPaintData data;
-    data.setProjectionMatrix(viewport.projectionMatrix());
-
     GLFramebuffer::pushFramebuffer(target);
     glClearColor(0.0, 0.0, 0.0, 0.0);
     glClear(GL_COLOR_BUFFER_BIT);
-    Compositor::self()->scene()->renderer()->renderItem(renderTarget, viewport, m_window->windowItem(), Scene::PAINT_WINDOW_TRANSFORMED, infiniteRegion(), data);
+    Compositor::self()->scene()->renderer()->renderItem(renderTarget, viewport, m_window->windowItem(), Scene::PAINT_WINDOW_TRANSFORMED, infiniteRegion(), WindowPaintData{});
     GLFramebuffer::popFramebuffer();
 }
 
diff --git a/src/plugins/screenshot/screenshot.cpp b/src/plugins/screenshot/screenshot.cpp
index 9e7479d816..54b27d7993 100644
--- a/src/plugins/screenshot/screenshot.cpp
+++ b/src/plugins/screenshot/screenshot.cpp
@@ -228,7 +228,6 @@ void ScreenShotEffect::takeScreenShot(ScreenShotWindowData *screenshot)
 {
     EffectWindow *window = screenshot->window;
 
-    WindowPaintData d;
     QRectF geometry = window->expandedGeometry();
     qreal devicePixelRatio = 1;
 
@@ -258,9 +257,6 @@ void ScreenShotEffect::takeScreenShot(ScreenShotWindowData *screenshot)
         validTarget = target->valid();
     }
     if (validTarget) {
-        d.setXTranslation(-geometry.x());
-        d.setYTranslation(-geometry.y());
-
         // render window into offscreen texture
         int mask = PAINT_WINDOW_TRANSFORMED | PAINT_WINDOW_TRANSLUCENT;
         QImage img;
@@ -272,10 +268,7 @@ void ScreenShotEffect::takeScreenShot(ScreenShotWindowData *screenshot)
             glClear(GL_COLOR_BUFFER_BIT);
             glClearColor(0.0, 0.0, 0.0, 1.0);
 
-            QMatrix4x4 projection;
-            projection.ortho(QRect(0, 0, geometry.width() * devicePixelRatio, geometry.height() * devicePixelRatio));
-            d.setProjectionMatrix(projection);
-
+            WindowPaintData d;
             effects->drawWindow(renderTarget, viewport, window, mask, infiniteRegion(), d);
 
             // copy content from framebuffer into image
diff --git a/src/plugins/thumbnailaside/thumbnailaside.cpp b/src/plugins/thumbnailaside/thumbnailaside.cpp
index 6f774eea16..21a388de95 100644
--- a/src/plugins/thumbnailaside/thumbnailaside.cpp
+++ b/src/plugins/thumbnailaside/thumbnailaside.cpp
@@ -62,7 +62,7 @@ void ThumbnailAsideEffect::paintScreen(const RenderTarget &renderTarget, const R
 
     for (const Data &d : std::as_const(windows)) {
         if (painted.intersects(d.rect)) {
-            WindowPaintData data(viewport.projectionMatrix());
+            WindowPaintData data;
             data.multiplyOpacity(opacity);
             QRect region;
             setPositionTransformations(data, region, d.window, d.rect, Qt::KeepAspectRatio);
diff --git a/src/scene/cursorscene.cpp b/src/scene/cursorscene.cpp
index 6f3ba58f57..49a118e9f3 100644
--- a/src/scene/cursorscene.cpp
+++ b/src/scene/cursorscene.cpp
@@ -58,7 +58,7 @@ void CursorScene::paint(const RenderTarget &renderTarget, const QRegion &region)
     RenderViewport viewport(QRectF(QPointF(), QSizeF(renderTarget.size()) / m_paintedOutput->scale()), m_paintedOutput->scale(), renderTarget);
     m_renderer->beginFrame(renderTarget, viewport);
     m_renderer->renderBackground(renderTarget, viewport, region);
-    m_renderer->renderItem(renderTarget, viewport, m_rootItem.get(), 0, region, WindowPaintData(viewport.projectionMatrix()));
+    m_renderer->renderItem(renderTarget, viewport, m_rootItem.get(), 0, region, WindowPaintData{});
     m_renderer->endFrame();
 }
 
diff --git a/src/scene/itemrenderer_opengl.cpp b/src/scene/itemrenderer_opengl.cpp
index 44ec0918e3..7f3a052ba3 100644
--- a/src/scene/itemrenderer_opengl.cpp
+++ b/src/scene/itemrenderer_opengl.cpp
@@ -260,7 +260,7 @@ void ItemRendererOpenGL::renderItem(const RenderTarget &renderTarget, const Rend
     }
 
     RenderContext renderContext{
-        .projectionMatrix = data.projectionMatrix(),
+        .projectionMatrix = viewport.projectionMatrix(),
         .clip = region,
         .hardwareClipping = region != infiniteRegion() && ((mask & Scene::PAINT_WINDOW_TRANSFORMED) || (mask & Scene::PAINT_SCREEN_TRANSFORMED)),
         .renderTargetScale = viewport.scale(),
diff --git a/src/scene/workspacescene.cpp b/src/scene/workspacescene.cpp
index 8c1614f0e8..7ff7e4b2c3 100644
--- a/src/scene/workspacescene.cpp
+++ b/src/scene/workspacescene.cpp
@@ -435,7 +435,7 @@ void WorkspaceScene::paintSimpleScreen(const RenderTarget &renderTarget, const R
     if (m_dndIcon) {
         const QRegion repaint = region & m_dndIcon->mapToGlobal(m_dndIcon->boundingRect()).toRect();
         if (!repaint.isEmpty()) {
-            m_renderer->renderItem(renderTarget, viewport, m_dndIcon.get(), 0, repaint, WindowPaintData(viewport.projectionMatrix()));
+            m_renderer->renderItem(renderTarget, viewport, m_dndIcon.get(), 0, repaint, WindowPaintData{});
         }
     }
 }
@@ -462,7 +462,7 @@ void WorkspaceScene::paintWindow(const RenderTarget &renderTarget, const RenderV
         return;
     }
 
-    WindowPaintData data(viewport.projectionMatrix());
+    WindowPaintData data;
     effects->paintWindow(renderTarget, viewport, item->effectWindow(), mask, region, data);
 }
 
diff --git a/src/scripting/windowthumbnailitem.cpp b/src/scripting/windowthumbnailitem.cpp
index d8b26d980e..d2b46747fe 100644
--- a/src/scripting/windowthumbnailitem.cpp
+++ b/src/scripting/windowthumbnailitem.cpp
@@ -117,6 +117,7 @@ void WindowThumbnailSource::update()
         if (!m_offscreenTexture) {
             return;
         }
+        m_offscreenTexture->setContentTransform(OutputTransform::FlipY);
         m_offscreenTexture->setFilter(GL_LINEAR);
         m_offscreenTexture->setWrapMode(GL_CLAMP_TO_EDGE);
         m_offscreenTarget = std::make_unique<GLFramebuffer>(m_offscreenTexture.get());
@@ -128,18 +129,11 @@ void WindowThumbnailSource::update()
     glClearColor(0.0, 0.0, 0.0, 0.0);
     glClear(GL_COLOR_BUFFER_BIT);
 
-    QMatrix4x4 projectionMatrix;
-    projectionMatrix.ortho(geometry.x() * devicePixelRatio, (geometry.x() + geometry.width()) * devicePixelRatio,
-                           geometry.y() * devicePixelRatio, (geometry.y() + geometry.height()) * devicePixelRatio, -1, 1);
-
-    WindowPaintData data;
-    data.setProjectionMatrix(projectionMatrix);
-
     // The thumbnail must be rendered using kwin's opengl context as VAOs are not
     // shared across contexts. Unfortunately, this also introduces a latency of 1
     // frame, which is not ideal, but it is acceptable for things such as thumbnails.
     const int mask = Scene::PAINT_WINDOW_TRANSFORMED;
-    Compositor::self()->scene()->renderer()->renderItem(offscreenRenderTarget, offscreenViewport, m_handle->windowItem(), mask, infiniteRegion(), data);
+    Compositor::self()->scene()->renderer()->renderItem(offscreenRenderTarget, offscreenViewport, m_handle->windowItem(), mask, infiniteRegion(), WindowPaintData{});
     GLFramebuffer::popFramebuffer();
 
     // The fence is needed to avoid the case where qtquick renderer starts using