Fix QNanoWidget OpenGL context usage

examples/gallery/main.cpp

@@ -10,6 +10,8 @@ int main(int argc, char *argv[])
     // load res from libqnanopainter
     Q_INIT_RESOURCE(libqnanopainterdata);
 
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
 #ifdef Q_OS_WIN
     // Select between OpenGL and OpenGL ES (Angle)
     //QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);

examples/helloitem/main.cpp

@@ -8,6 +8,8 @@ int main(int argc, char *argv[])
     // load res from libqnanopainter
     Q_INIT_RESOURCE(libqnanopainterdata);
 
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
 #ifdef Q_OS_WIN
     // Select between OpenGL and OpenGL ES (Angle)
     //QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);

examples/hellowidget/main.cpp

@@ -27,6 +27,8 @@ int main(int argc, char *argv[])
     // load res from libqnanopainter
     Q_INIT_RESOURCE(libqnanopainterdata);
 
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
 #ifdef Q_OS_WIN
     // Select between OpenGL and OpenGL ES (Angle)
     //QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);

examples/hellowindow/main.cpp

@@ -27,6 +27,8 @@ int main(int argc, char *argv[])
     // load res from libqnanopainter
     Q_INIT_RESOURCE(libqnanopainterdata);
 
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
 #ifdef Q_OS_WIN
     // Select between OpenGL and OpenGL ES (Angle)
     //QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);

examples/qnanopainter_vs_qpainter_demo/main.cpp

@@ -13,6 +13,8 @@ int main(int argc, char *argv[])
     // load res from libqnanopainter
     Q_INIT_RESOURCE(libqnanopainterdata);
 
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
 #ifdef Q_OS_WIN
     // Select between OpenGL and OpenGL ES (Angle)
     //QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);

libqnanopainter/qnanopainter.cpp

@@ -138,6 +138,16 @@ Q_GLOBAL_STATIC(QNanoPainter, instance)
 QNanoPainter::QNanoPainter()
 {
 #ifndef QNANO_USE_RHI
+    // Save current OpenGL context so it can be restored later
+    QOpenGLContext *prevContext = QOpenGLContext::currentContext();
+
+    // Create new OpenGL context that can be owned by this QNanoPainter object
+    Q_ASSERT(QCoreApplication::testAttribute(Qt::AA_ShareOpenGLContexts));
+    m_openglContext.setShareContext(QOpenGLContext::globalShareContext());
+    m_openglContext.create();
+    m_openglSurface.setFormat(m_openglContext.format());
+    m_openglSurface.create();
+    m_openglContext.makeCurrent(&m_openglSurface);
 
     // Request actual OpenGL context version and type
     QOpenGLContext *context = QOpenGLContext::currentContext();
@@ -156,6 +166,10 @@ QNanoPainter::QNanoPainter()
     m_nvgContext = m_backend->nvgCreate(NVG_ANTIALIAS);
     Q_ASSERT_X(m_nvgContext, "QNanoPainter::QNanoPainter", "Could not init nanovg!");
 
+    // Restore previous OpenGL context
+    if (prevContext != nullptr)
+        prevContext->makeCurrent(prevContext->surface());
+
 #else
     m_backend.reset(QNanoBackendFactory::createBackend(0, 0, false));
 #endif
@@ -171,9 +185,12 @@ QNanoPainter::QNanoPainter()
 
 QNanoPainter::~QNanoPainter()
 {
+    if (m_backend && m_nvgContext) {
+
+#ifndef QNANO_USE_RHI
+        m_openglContext.makeCurrent(&m_openglSurface);
+#endif
 
-    if (m_backend && m_nvgContext && QOpenGLContext::currentContext()) {
-        // Do NanoVG side cleanups only if OpenGL context still exists
         m_backend->nvgDelete(m_nvgContext);
     }
 

libqnanopainter/qnanopainter.h

@@ -27,6 +27,8 @@
 #include <QTransform>
 #include <QSharedPointer>
 #include <QSurfaceFormat>
+#include <QOpenGLContext>
+#include <QOffscreenSurface>
 #include "qnanocolor.h"
 #include "private/qnanobrush.h"
 #include "private/qnanodataelement.h"
@@ -299,6 +301,10 @@ class QNanoPainter
     QSharedPointer<QNanoFont> m_defaultFont;
     QString m_openglContextName;
 
+#ifndef QNANO_USE_RHI
+    QOpenGLContext m_openglContext;
+    QOffscreenSurface m_openglSurface;
+#endif
 };
 
 #endif // QNANOPAINTER_H