[vlc-commits] [Git][videolan/vlc][master] qt: handle source item and window deviation in `TextureProviderObserver`

[Steve Lhomme (@robUx4)]

Steve Lhomme pushed to branch master at VideoLAN / VLC


Commits:
5f3c01fc by Fatih Uzunoglu at 2025-09-18T11:59:35+00:00
qt: handle source item and window deviation in `TextureProviderObserver`

The source item and window may change and thus deviate from the captured
ones before the window starts synchronizing in the current or the next
frame (depending on what the stage is currently).

- - - - -


2 changed files:

- modules/gui/qt/util/textureproviderobserver.cpp
- modules/gui/qt/util/textureproviderobserver.hpp


Changes:

=====================================
modules/gui/qt/util/textureproviderobserver.cpp
=====================================
@@ -18,6 +18,7 @@
 #include "textureproviderobserver.hpp"
 
 #include <QSGTextureProvider>
+#include <QQmlInfo>
 
 #if __has_include(<rhi/qrhi.h>) // RHI is semi-public since Qt 6.6
 #define RHI_HEADER_AVAILABLE
@@ -30,9 +31,9 @@ TextureProviderObserver::TextureProviderObserver(QObject *parent)
 
 }
 
-void TextureProviderObserver::setSource(const QQuickItem *source)
+void TextureProviderObserver::setSource(const QQuickItem *source, bool enforce)
 {
-    if (m_source == source)
+    if (!enforce && (m_source == source))
         return;
 
     {
@@ -59,12 +60,34 @@ void TextureProviderObserver::setSource(const QQuickItem *source)
     {
         assert(m_source->isTextureProvider());
 
-        const auto init = [this]() {
+        const auto init = [this, enforce]() {
             const auto window = m_source->window();
             assert(window);
 
-            connect(window, &QQuickWindow::beforeSynchronizing, this, [this, window]() {
-                assert(m_source->window() == window);
+            connect(window, &QQuickWindow::beforeSynchronizing, this, [this, window, source = m_source, enforce]() {
+                if (Q_UNLIKELY(source != m_source)) // either different or null pointer
+                    return; // we can simply return here, as if new source is valid a new connection would be established (this slot becomes stale either way)
+
+                if (Q_UNLIKELY(m_source->window() != window))
+                {
+                    // This may happen if the source item changes its window before its old window starts synchronizing in the current or the next frame.
+                    // There may be two situations:
+                    // - Source item has a new valid window. This may happen if the item is moved to another window (such as by adjusting visual parent).
+                    //   In this case it would be fine to continue if multiple windows are bound to the same rendering thread, but better to not risk it.
+                    // - Source item no longer has a window. This is more likely than the former.
+                    qmlDebug(this) << "source item's window: " << m_source->window() << " is not matching with the captured one: " << window << ". Trying again...";
+                    QMetaObject::invokeMethod(this, [this, enforce]() {
+                        if (Q_UNLIKELY(enforce))
+                        {
+                            qmlWarning(this) << "source item changed its window again, bailing out.";
+                            setSource(nullptr); // bail out, tried once
+                        }
+                        else
+                            setSource(m_source, true);
+                    }, Qt::QueuedConnection);
+                    return;
+                }
+
                 assert(!m_provider);
 
                 m_provider = m_source->textureProvider(); // This can only be called in the rendering thread.


=====================================
modules/gui/qt/util/textureproviderobserver.hpp
=====================================
@@ -66,7 +66,7 @@ class TextureProviderObserver : public QObject
 public:
     explicit TextureProviderObserver(QObject *parent = nullptr);
 
-    void setSource(const QQuickItem* source);
+    void setSource(const QQuickItem* source, bool enforce = false);
     QSize textureSize() const;
     QSize nativeTextureSize() const;
     bool hasAlphaChannel() const;



View it on GitLab: https://code.videolan.org/videolan/vlc/-/commit/5f3c01fc06d6b5cec2bc14178e6fafa35039ed4a

-- 
View it on GitLab: https://code.videolan.org/videolan/vlc/-/commit/5f3c01fc06d6b5cec2bc14178e6fafa35039ed4a
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