perf: render RV viewport as a native GL window to fix Qt6 web-panel latency

The Qt6/PySide6 migration regressed the JS->Python QWebChannel bridge in
docked QWebEngineView panels: pyevaluate round-trips grew unbounded (into the
seconds) while media plays, where Qt5 stayed flat (~8 ms). Root cause is the
per-presented-frame ~80-90 ms full-window QOpenGLWidget composite, which
serializes on the GUI thread and starves QWebChannel delivery. The two prior
fixes (edit-mode churn skip, settle-window removal) only address the
non-playing path, so the regression persisted whenever a handler started
playback.

Render the RV viewport as a native QOpenGLWindow (new GLWindow) embedded via
QWidget::createWindowContainer, instead of a QOpenGLWidget:

- The top-level QMainWindow is no longer forced onto the OpenGL RHI backend,
  so docked QWebEngineView panels render on the platform-default backend and
  QT_QUICK_BACKEND=software is no longer needed (removed).
- The viewport presents on its own surface, off the full-window widget
  composite, so playback no longer starves the bridge. Bridge latency stays
  flat and self-healing while playing.

GLView becomes a plain QWidget host that delegates the API RV expects to the
GLWindow; QTGLVideoDevice gains a window-backed path alongside the widget one.

Also fixed, exposed by the surface change:

- Presentation / second output: DesktopVideoDevice::open no longer dereferences
  the control device's (now-null) QOpenGLWidget; ScreenView shares a
  QOpenGLContext via new backing-agnostic QTGLVideoDevice::glShareContext()/
  glSurfaceFormat().
- Set Qt::AA_ShareOpenGLContexts (documented QtWebEngine requirement) so the
  second-output and upload-worker GL surfaces share with the viewport, and drop
  a null-context dereference in newSharedContextWorkerDevice that crashed when
  Multithread GPU Upload was enabled.
- The UI blocking overlay is reworked from a raster child widget into a
  frameless translucent top-level window so it can dim and block input over the
  native viewport.

Validated on Windows (release): flat bridge latency under playback spam, all
web panels render docked, and viewport/events/drag-drop/annotations/
presentation/blocking-overlay all work. macOS and HDPI passes still pending.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

Author: cedrik-fuoco-adsk

docs/rv-manuals/rv-reference-manual/rv-reference-manual-chapter-four.md

@@ -236,7 +236,9 @@ import rv.qtutils
 # Gets the current RV session windows as a PySide QMainWindow.
 rvSessionWindow = rv.qtutils.sessionWindow()
 
-# Gets the current RV session GL view as a PySide QGLWidget.
+# Gets the current RV session view host as a PySide QWidget. Note: the GL
+# viewport is now a native child window embedded in this host (via
+# createWindowContainer), so this is a plain QWidget, not a QOpenGLWidget.
 rvSessionGLView = rv.qtutils.sessionGLView()
 
 # Gets the current RV session top tool bar as a PySide QToolBar.

src/bin/apps/rv/main.cpp

@@ -356,7 +356,14 @@ int utf8Main(int argc, char* argv[])
     // Qt 5.12.1 specific
     // Disable Qt Quick hardware rendering because QwebEngineView conflicts with
     // QGLWidget
-    setEnvVar("QT_QUICK_BACKEND", "software");
+    //
+    // Direction C: the RV viewport is now a native GL window (GLWindow) hosted
+    // via createWindowContainer, not a QOpenGLWidget. The main window no longer
+    // forces the OpenGL RHI backend, so QtWebEngine's QQuickWidget can composite
+    // on the platform default backend at hardware speed. The old software Qt
+    // Quick workaround (which caused the ~77 ms per-frame web-view composite) is
+    // therefore no longer needed.
+    // setEnvVar("QT_QUICK_BACKEND", "software");
 
 #if defined(PLATFORM_LINUX)
     // Work around for Wacom Tablet issue on linux
@@ -369,6 +376,14 @@ int utf8Main(int argc, char* argv[])
     // (RV Preferences/Rendering/Multithread GPU Upload)
     QApplication::setAttribute(Qt::AA_DontCheckOpenGLContextThreadAffinity);
 
+    // Share GL resources across every QOpenGLContext in the process. This is a
+    // documented QtWebEngine requirement, and it lets RV's auxiliary GL
+    // surfaces -- the second-output ScreenView and the multithreaded-upload
+    // worker device -- share textures/FBOs with the main viewport context
+    // without an explicit, ordering-sensitive setShareContext() call. Must be
+    // set before the QApplication is constructed.
+    QApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
     TwkUtil::MemPool::initialize();
 
     string altPrefsPath;

src/lib/app/RvCommon/CMakeLists.txt

@@ -48,6 +48,7 @@ SET(_sources
     RvApplication.cpp
     DiagnosticsView.cpp
     GLView.cpp
+    GLWindow.cpp
     TwkQTAction.cpp
     MediaDirModel.cpp
     RvNetworkDialog.cpp

src/lib/app/RvCommon/DesktopVideoDevice.cpp

@@ -157,10 +157,10 @@ namespace Rv
     {
         TWK_GLDEBUG;
 
-        QSurfaceFormat fmt = shareDevice()->widget()->format();
+        QSurfaceFormat fmt = shareDevice()->glSurfaceFormat();
         fmt.setSwapInterval(m_vsync ? 1 : 0);
 
-        ScreenView* vw = new ScreenView(fmt, 0, shareDevice()->widget(), Qt::Window);
+        ScreenView* vw = new ScreenView(fmt, 0, shareDevice()->glShareContext(), Qt::Window);
         setViewWidget(vw);
 
         QTGLVideoDevice* vd = new QTGLVideoDevice(0, "local view", vw);
@@ -747,11 +747,11 @@ namespace Rv
 
     void DesktopVideoDevice::sortVideoFormatsByWidth() { sort(m_videoFormats.begin(), m_videoFormats.end(), widthSort); }
 
-    DesktopVideoDevice::ScreenView::ScreenView(const QSurfaceFormat& fmt, QWidget* parent, QOpenGLWidget* glViewShare,
+    DesktopVideoDevice::ScreenView::ScreenView(const QSurfaceFormat& fmt, QWidget* parent, QOpenGLContext* glShareContext,
                                                Qt::WindowFlags flags)
         : QOpenGLWidget(parent, flags)
     {
-        m_glViewShare = glViewShare;
+        m_glShareContext = glShareContext;
         setFormat(fmt);
 
         // Important: set PartialUpdate, because otherwise
@@ -764,9 +764,9 @@ namespace Rv
     {
         QOpenGLWidget::initializeGL();
 
-        if (m_glViewShare && context() && context()->isValid())
+        if (m_glShareContext && context() && context()->isValid())
         {
-            context()->setShareContext(m_glViewShare->context());
+            context()->setShareContext(m_glShareContext);
         }
     }