Fix crash in MultiEffect with dynamic delegates

Changing dummy QQuickShaderEffectSource to be private variable rather
than static one fixes issue with dynamic delegates switching blurred
items on/off.

Fixes: QTBUG-124730
Change-Id: Ibaebfd6cb228fe1b7fa91c8219c1355a93ceb19c
Reviewed-by: Laszlo Agocs <[email protected]>
Reviewed-by: Tomi Korpipää <[email protected]>
Reviewed-by: Eskil Abrahamsen Blomfeldt <[email protected]>
(cherry picked from commit 4375fff77441e11efc814a959950580d5b3645b5)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>
(cherry picked from commit 0fde572310ac0c834d8b04a85afa150e6223ae75)

2 files changed, 5 insertions, 2 deletions

diff --git a/src/effects/qquickmultieffect.cpp b/src/effects/qquickmultieffect.cpp
index 6b20c3fa14..7561649fbf 100644
--- a/src/effects/qquickmultieffect.cpp
+++ b/src/effects/qquickmultieffect.cpp
@@ -1697,11 +1697,12 @@ void QQuickMultiEffectPrivate::updateBlurItemsAmount(int blurLevel)
     }
 
     // Set the blur items source components
-    static const auto dummyShaderSource = new QQuickShaderEffectSource(q);
+    if (!m_dummyShaderSource)
+        m_dummyShaderSource = new QQuickShaderEffectSource(q);
     for (int i = 0; i < m_blurEffects.size(); i++) {
         auto *blurEffect = m_blurEffects[i];
         auto sourceItem = (i >= itemsAmount) ?
-                    static_cast<QQuickItem *>(dummyShaderSource) : (i == 0) ?
+                    static_cast<QQuickItem *>(m_dummyShaderSource) : (i == 0) ?
                         static_cast<QQuickItem *>(m_shaderSource->output()) :
                         static_cast<QQuickItem *>(m_blurEffects[i - 1]);
         auto sourceVariant = QVariant::fromValue<QQuickItem*>(sourceItem);
diff --git a/src/effects/qquickmultieffect_p_p.h b/src/effects/qquickmultieffect_p_p.h
index 2df33db45b..7d635e2e25 100644
--- a/src/effects/qquickmultieffect_p_p.h
+++ b/src/effects/qquickmultieffect_p_p.h
@@ -27,6 +27,7 @@ QT_REQUIRE_CONFIG(quick_shadereffect);
 QT_BEGIN_NAMESPACE
 
 class QQuickShaderEffect;
+class QQuickShaderEffectSource;
 
 class QQuickMultiEffectPrivate : public QQuickItemPrivate
 {
@@ -145,6 +146,7 @@ private:
     QQuickItem *m_sourceItem = nullptr;
     QGfxSourceProxy *m_shaderSource = nullptr;
     QQuickShaderEffect *m_shaderEffect = nullptr;
+    QQuickShaderEffectSource *m_dummyShaderSource = nullptr;
     QVector<QQuickShaderEffect *> m_blurEffects;
     bool m_autoPaddingEnabled = true;
     QRectF m_paddingRect;