Resolve compositing glitches

interface/src/Application.cpp

@@ -2736,7 +2736,36 @@ void Application::initializeGL() {
     // We have to account for this possibility by checking here for an existing 
     // global share context
     auto globalShareContext = qt_gl_global_share_context();
-    _glWidget->createContext(globalShareContext); 
+    
+#if !defined(DISABLE_QML)
+    // Build a shared canvas / context for the Chromium processes
+    if (!globalShareContext) {
+        // Chromium rendering uses some GL functions that prevent nSight from capturing
+        // frames, so we only create the shared context if nsight is NOT active.
+        if (!nsightActive()) {
+            _chromiumShareContext = new OffscreenGLCanvas();
+            _chromiumShareContext->setObjectName("ChromiumShareContext");
+            auto format =QSurfaceFormat::defaultFormat();
+#ifdef Q_OS_MAC
+            // On mac, the primary shared OpenGL context must be a 3.2 core context,
+            // or chromium flips out and spews error spam (but renders fine)
+            format.setMajorVersion(3);
+            format.setMinorVersion(2);
+#endif
+            _chromiumShareContext->setFormat(format);
+            _chromiumShareContext->create();
+            if (!_chromiumShareContext->makeCurrent()) {
+                qCWarning(interfaceapp, "Unable to make chromium shared context current");
+            }
+            globalShareContext = _chromiumShareContext->getContext();
+            qt_gl_set_global_share_context(globalShareContext);
+            _chromiumShareContext->doneCurrent();
+        }
+    }
+#endif
+
+
+    _glWidget->createContext(globalShareContext);
 
     if (!_glWidget->makeCurrent()) {
         qCWarning(interfaceapp, "Unable to make window context current");
@@ -2749,27 +2778,6 @@ void Application::initializeGL() {
     if ((vendor.find("AMD") != std::string::npos) || (vendor.find("ATI") != std::string::npos)) {
         qputenv("QTWEBENGINE_CHROMIUM_FLAGS", QByteArray("--disable-distance-field-text"));
     }
-
-    // Build a shared canvas / context for the Chromium processes
-    if (!globalShareContext) {
-        // Chromium rendering uses some GL functions that prevent nSight from capturing
-        // frames, so we only create the shared context if nsight is NOT active.
-        if (!nsightActive()) {
-           _chromiumShareContext = new OffscreenGLCanvas();
-            _chromiumShareContext->setObjectName("ChromiumShareContext");
-            _chromiumShareContext->create(_glWidget->qglContext());
-            if (!_chromiumShareContext->makeCurrent()) {
-                qCWarning(interfaceapp, "Unable to make chromium shared context current");
-            }
-            globalShareContext = _chromiumShareContext->getContext();
-            qt_gl_set_global_share_context(globalShareContext);
-            _chromiumShareContext->doneCurrent();
-            // Restore the GL widget context
-            if (!_glWidget->makeCurrent()) {
-                qCWarning(interfaceapp, "Unable to make window context current");
-            }
-        }
-    }
 #endif
 
     if (!globalShareContext) {

libraries/display-plugins/src/display-plugins/OpenGLDisplayPlugin.cpp

@@ -179,7 +179,9 @@ public:
             _context->makeCurrent();
             {
                 PROFILE_RANGE(render, "PluginPresent")
+                gl::globalLock();
                 currentPlugin->present();
+                gl::globalRelease(false);
                 CHECK_GL_ERROR();
             }
             _context->doneCurrent();

libraries/gl/src/gl/GLHelpers.cpp

@@ -34,6 +34,41 @@ bool gl::disableGl45() {
 #endif
 }
 
+#ifdef Q_OS_MAC
+#define SERIALIZE_GL_RENDERING
+#endif
+
+#ifdef SERIALIZE_GL_RENDERING
+
+// This terrible terrible hack brought to you by the complete lack of reasonable
+// OpenGL debugging tools on OSX.  Without this serialization code, the UI textures
+// frequently become 'glitchy' and get composited onto the main scene in what looks
+// like a partially rendered state.
+// This looks very much like either state bleeding across the contexts, or bad
+// synchronization for the shared OpenGL textures.  However, previous attempts to resolve
+// it, even with gratuitous use of glFinish hasn't improved the situation
+
+static std::mutex _globalOpenGLLock;
+
+void gl::globalLock() {
+    _globalOpenGLLock.lock();
+}
+
+void gl::globalRelease(bool finish) {
+    if (finish) {
+        glFinish();
+    }
+    _globalOpenGLLock.unlock();
+}
+
+#else
+
+void gl::globalLock() {}
+void gl::globalRelease(bool finish) {}
+
+#endif
+
+
 void gl::getTargetVersion(int& major, int& minor) {
 #if defined(USE_GLES)
     major = 3;

libraries/gl/src/gl/GLHelpers.h

@@ -35,6 +35,9 @@ int glVersionToInteger(QString glVersion);
 bool isRenderThread();
 
 namespace gl {
+    void globalLock();
+    void globalRelease(bool finish = true);
+    
     void withSavedContext(const std::function<void()>& f);
 
     bool checkGLError(const char* name);

libraries/gl/src/gl/OffscreenGLCanvas.cpp

@@ -33,6 +33,7 @@ OffscreenGLCanvas::OffscreenGLCanvas() :
     _context(new QOpenGLContext),
     _offscreenSurface(new QOffscreenSurface)
 {
+    setFormat(getDefaultOpenGLSurfaceFormat());
 }
 
 OffscreenGLCanvas::~OffscreenGLCanvas() {
@@ -49,12 +50,15 @@ OffscreenGLCanvas::~OffscreenGLCanvas() {
 
 }
 
+void OffscreenGLCanvas::setFormat(const QSurfaceFormat& format) {
+    _context->setFormat(format);
+}
+    
 bool OffscreenGLCanvas::create(QOpenGLContext* sharedContext) {
     if (nullptr != sharedContext) {
         sharedContext->doneCurrent();
         _context->setShareContext(sharedContext);
     }
-    _context->setFormat(getDefaultOpenGLSurfaceFormat());
     if (!_context->create()) {
         qFatal("Failed to create OffscreenGLCanvas context");
     }

libraries/gl/src/gl/OffscreenGLCanvas.h

@@ -18,11 +18,13 @@
 class QOpenGLContext;
 class QOffscreenSurface;
 class QOpenGLDebugMessage;
+class QSurfaceFormat;
 
 class OffscreenGLCanvas : public QObject {
 public:
     OffscreenGLCanvas();
     ~OffscreenGLCanvas();
+    void setFormat(const QSurfaceFormat& format);
     bool create(QOpenGLContext* sharedContext = nullptr);
     bool makeCurrent();
     void doneCurrent();

libraries/qml/src/qml/impl/RenderEventHandler.cpp

@@ -12,6 +12,7 @@
 
 #include <gl/Config.h>
 #include <gl/QOpenGLContextWrapper.h>
+#include <gl/GLHelpers.h>
 
 #include <QtQuick/QQuickWindow>
 
@@ -114,6 +115,7 @@ void RenderEventHandler::onRender() {
 
     PROFILE_RANGE(render_qml_gl, __FUNCTION__);
 
+    gl::globalLock();
     if (!_shared->preRender()) {
         return;
     }
@@ -144,6 +146,7 @@ void RenderEventHandler::onRender() {
         _shared->updateTextureAndFence({ texture, fence });
         _shared->_quickWindow->resetOpenGLState();
     }
+    gl::globalRelease();
 }
 
 void RenderEventHandler::onQuit() {