Add sharedresource example

Won't yet work, obviously.

examples/rhi/multiwindow/multiwindow.cpp

@@ -553,11 +553,6 @@ int main(int argc, char **argv)
     qDebug("Selected graphics API is %s", qPrintable(graphicsApiName()));
     qDebug("This is a multi-api example, use command line arguments to override:\n%s", qPrintable(cmdLineParser.helpText()));
 
-    QSurfaceFormat fmt;
-    fmt.setDepthBufferSize(24);
-    fmt.setStencilBufferSize(8);
-    QSurfaceFormat::setDefaultFormat(fmt);
-
 #if QT_CONFIG(vulkan)
     r.instance = new QVulkanInstance;
     if (graphicsApi == Vulkan) {

examples/rhi/multiwindow_threaded/multiwindow_threaded.cpp

@@ -760,8 +760,8 @@ int main(int argc, char **argv)
     QVBoxLayout *layout = new QVBoxLayout(&w);
 
     QPlainTextEdit *info = new QPlainTextEdit(
-                QLatin1String("This application tests rendering on a separate thread per window, with dedicated QRhi instances. " // ### still sharing the same graphics device where applicable
-                              "No resources are shared across windows here. "
+                QLatin1String("This application tests rendering on a separate thread per window, with dedicated QRhi instances. "
+                              "No resources are shared across windows here. (QRhiResourceSharingHost is not used) "
                               "\n\nThis is the same concept as the Qt Quick Scenegraph's threaded render loop. This should allow rendering to the different windows "
                               "without unintentionally throttling each other's threads."
                               "\n\nUsing API: ") + graphicsApiName());

examples/rhi/rhi.pro

@@ -12,6 +12,7 @@ SUBDIRS += \
     multiwindow_threaded \
     imguidemo \
     triquadcube \
+    sharedresource \
     offscreen
 
 qtConfig(vulkan) {

examples/rhi/shared/examplefw.h

@@ -417,7 +417,7 @@ void Window::render()
 
 #ifdef Q_OS_DARWIN
     if (!scFlags.testFlag(QRhiSwapChain::NoVSync))
-        requestUpdate(); // CVDisplayLink (not strictly needed on macOS with Metal)
+        requestUpdate(); // CVDisplayLink
     else
         QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
 #else

examples/rhi/sharedresource/sharedresource.pro

+TEMPLATE = app
+
+QT += shadertools rhi
+
+SOURCES = \
+    sharedresource.cpp
+
+RESOURCES = sharedresource.qrc
+
+target.path = $$[QT_INSTALL_EXAMPLES]/rhi/sharedresource
+INSTALLS += target

examples/rhi/sharedresource/sharedresource.qrc

+<!DOCTYPE RCC><RCC version="1.0">
+<qresource>
+  <file alias="texture.vert.qsb">../shared/texture.vert.qsb</file>
+  <file alias="texture.frag.qsb">../shared/texture.frag.qsb</file>
+  <file alias="qt256.png">../shared/qt256.png</file>
+</qresource>
+</RCC>

src/rhi/qrhi.cpp

@@ -227,8 +227,8 @@ QT_BEGIN_NAMESPACE
 
     A QRhi instance can be created and used on any thread but all usage must be
     limited to that one single thread. When it comes to native objects, such as
-    OpenGL contexts, passed in in QRhiInitParams, it is up to the application
-    to ensure they are not misused by other threads.
+    OpenGL contexts, passed in via a QRhiNativeHandles subclass, it is up to
+    the application to ensure they are not misused by other threads.
 
     \sa {Qt Shader Tools}
  */
@@ -2536,11 +2536,6 @@ quint32 QRhiImplementation::approxByteSizeForTexture(QRhiTexture::Format format,
     it also performs synchronizing submission to the device context (of which
     there is only one, regardless of the number of threads submitting to it).
 
-    \note There is no further synchronization performed for resources like
-    buffers or textures. If the QRhi instances operate on different threads, it
-    is up to those threads to ensure the QRhiResource usages on the threads
-    are done as appropriate for the underlying graphics APIs.
-
     \note The QRhiResourceSharingHost can be created on a thread that is
     different than the threads on which the associated QRhi instances will be
     created. It is however up to the application to organize those threads in a

todo.txt

-multiple qrhis on threads with shared resources - how
+res.sh.: reuse device / create sharing context
+res.sh.: example to show using same texture
+res.sh.: example to show read/write same texture
+res.sh.: d3d context sync
+res.sh.: exercise it in multiwindow_threaded too
 advanced blend modes
 gl: tex formats (texture, readback)
 gl: srgb