From 97a82c97df74a4701b8ec384ccf44bb944945f35 Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Fri, 27 May 2022 17:20:56 +0300
Subject: [PATCH] effects: Fix QQuickItem::mapToGlobal() in qtquick effects on
 wayland

On Wayland, we create a dummy window to fix HiDPI issues. At the moment,
the QQuickRenderControl::renderWindow() returns a fixed offset 0,0.

As it turns out, QQuickItem::mapToGlobal() will poke the
QQuickRenderControl::renderWindow() function to map the specified point
to the global coordinate space.

Since the renderWindow() function returns hardcoded offset, the
mapToGlobal() function is sort of broken in fullscreen effects.

In order to fix mapToGlobal() on Wayland, this change makes the
EffectQuickRenderControl return the position of the associated
OffscreenQuickView.
---
 src/libkwineffects/kwinoffscreenquickview.cpp | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/libkwineffects/kwinoffscreenquickview.cpp b/src/libkwineffects/kwinoffscreenquickview.cpp
index b18af17f40..ad285675bb 100644
--- a/src/libkwineffects/kwinoffscreenquickview.cpp
+++ b/src/libkwineffects/kwinoffscreenquickview.cpp
@@ -40,8 +40,9 @@ class EffectQuickRenderControl : public QQuickRenderControl
     Q_OBJECT
 
 public:
-    explicit EffectQuickRenderControl(QWindow *renderWindow, QObject *parent = nullptr)
-        : QQuickRenderControl(parent)
+    explicit EffectQuickRenderControl(OffscreenQuickView *view, QWindow *renderWindow)
+        : QQuickRenderControl(view)
+        , m_view(view)
         , m_renderWindow(renderWindow)
     {
     }
@@ -49,12 +50,17 @@ public:
     QWindow *renderWindow(QPoint *offset) override
     {
         if (offset) {
-            *offset = QPoint(0, 0);
+            if (m_renderWindow) {
+                *offset = m_renderWindow->mapFromGlobal(m_view->geometry().topLeft());
+            } else {
+                *offset = QPoint(0, 0);
+            }
         }
         return m_renderWindow;
     }
 
 private:
+    OffscreenQuickView *m_view;
     QPointer<QWindow> m_renderWindow;
 };
 
@@ -125,7 +131,7 @@ OffscreenQuickView::OffscreenQuickView(QObject *parent, QWindow *renderWindow, E
     : QObject(parent)
     , d(new OffscreenQuickView::Private)
 {
-    d->m_renderControl = new EffectQuickRenderControl(renderWindow, this);
+    d->m_renderControl = new EffectQuickRenderControl(this, renderWindow);
 
     d->m_view = new QQuickWindow(d->m_renderControl);
     d->m_view->setFlags(Qt::FramelessWindowHint);