[XR/XrSession] Requesting frame rendering returns whether it has been

- This is used afterward to avoid copying the frame to the window

- It happens for the first few frames, notably when the session hasn't been started yet (the RenderSystem is updated while the XrSystem still hasn't been)

include/RaZ/XR/XrSession.hpp

@@ -42,7 +42,7 @@ class XrSession {
 
   void begin(unsigned int viewConfigType);
   void end();
-  void renderFrame(const std::vector<XrViewConfigurationView>& viewConfigViews,
+  bool renderFrame(const std::vector<XrViewConfigurationView>& viewConfigViews,
                    unsigned int viewConfigType,
                    unsigned int environmentBlendMode,
                    const ViewRenderFunc& viewRenderFunc);

include/RaZ/XR/XrSystem.hpp

@@ -26,7 +26,7 @@ class XrSystem final : public System {
 
 private:
   Vec2u recoverOptimalViewSize() const;
-  void renderFrame(const ViewRenderFunc& viewRenderFunc);
+  bool renderFrame(const ViewRenderFunc& viewRenderFunc);
 
   void recoverViewConfigurations();
   void recoverEnvironmentBlendModes();

src/RaZ/Render/RenderSystem.cpp

@@ -297,7 +297,7 @@ void RenderSystem::renderXrFrame() {
   ZoneScopedN("RenderSystem::renderXrFrame");
   TracyGpuZone("RenderSystem::renderXrFrame")
 
-  m_xrSystem->renderFrame([this] (Vec3f position, Quaternionf rotation, ViewFov viewFov) {
+  const bool hasRendered = m_xrSystem->renderFrame([this] (Vec3f position, Quaternionf rotation, ViewFov viewFov) {
     if (m_cameraEntity) {
       const auto& camTransform = m_cameraEntity->getComponent<Transform>();
       position = camTransform.getRotation() * position + camTransform.getPosition();
@@ -342,6 +342,9 @@ void RenderSystem::renderXrFrame() {
   });
 
 #if !defined(RAZ_NO_WINDOW)
+  if (!hasRendered)
+    return;
+
   // TODO: the copied color buffer must be the one from the render pass executed last
   const Framebuffer& geomFramebuffer = m_renderGraph.m_geometryPass.getFramebuffer();
   copyToWindow(geomFramebuffer.getColorBuffer(0), geomFramebuffer.getDepthBuffer(), m_window->getWidth(), m_window->getHeight());

src/RaZ/XR/XrSession.cpp

@@ -232,14 +232,14 @@ void XrSession::end() {
   Logger::debug("[XrSession] Ended session");
 }
 
-void XrSession::renderFrame(const std::vector<XrViewConfigurationView>& viewConfigViews,
+bool XrSession::renderFrame(const std::vector<XrViewConfigurationView>& viewConfigViews,
                             unsigned int viewConfigType,
                             unsigned int environmentBlendMode,
                             const ViewRenderFunc& viewRenderFunc) {
   ZoneScopedN("XrSession::renderFrame");
 
   if (!m_isRunning)
-    return;
+    return false;
 
   XrFrameWaitInfo frameWaitInfo {};
   frameWaitInfo.type = XR_TYPE_FRAME_WAIT_INFO;
@@ -275,6 +275,8 @@ void XrSession::renderFrame(const std::vector<XrViewConfigurationView>& viewConf
     frameEndInfo.layers               = renderLayerInfo.layers.data();
     checkLog(xrEndFrame(m_handle, &frameEndInfo), "Failed to end the XR frame", m_instance);
   }
+
+  return !renderLayerInfo.layers.empty();
 }
 
 XrSession::~XrSession() {

src/RaZ/XR/XrSystem.cpp

@@ -117,8 +117,8 @@ Vec2u XrSystem::recoverOptimalViewSize() const {
   return optimalViewSize;
 }
 
-void XrSystem::renderFrame(const ViewRenderFunc& viewRenderFunc) {
-  m_session.renderFrame(m_viewConfigViews, m_viewConfigType, m_environmentBlendMode, viewRenderFunc);
+bool XrSystem::renderFrame(const ViewRenderFunc& viewRenderFunc) {
+  return m_session.renderFrame(m_viewConfigViews, m_viewConfigType, m_environmentBlendMode, viewRenderFunc);
 }
 
 void XrSystem::recoverViewConfigurations() {