multiwindow examples: handle zero size

examples/rhi/multiwindow/multiwindow.cpp

@@ -363,12 +363,13 @@ void Window::exposeEvent(QExposeEvent *)
         render();
     }
 
-    // stop pushing frames when not exposed (on some platforms this is essential, optional on others)
-    if (!isExposed() && m_running)
+    // stop pushing frames when not exposed (or size is 0)
+    if ((!isExposed() || (m_hasSwapChain && m_sc->surfacePixelSize().isEmpty())) && m_running)
         m_notExposed = true;
 
-    // continue when exposed again
-    if (isExposed() && m_running && m_notExposed) {
+    // continue when exposed again and the surface has a valid size.
+    // note that the surface size can be (0, 0) even though size() reports a valid one...
+    if (isExposed() && m_running && m_notExposed && !m_sc->surfacePixelSize().isEmpty()) {
         m_notExposed = false;
         m_newlyExposed = true;
         render();

examples/rhi/multiwindow_threaded/multiwindow_threaded.cpp

@@ -566,21 +566,41 @@ void Renderer::render(bool newlyExposed, bool wakeBeforePresent)
         m_proj.translate(0, 0, -4);
     };
 
-    if (newlyExposed || m_sc->currentPixelSize() != m_sc->surfacePixelSize())
+    auto wakeUpIfNeeded = [wakeBeforePresent, this] {
+        // make sure the main/gui thread is not blocked when issuing the Present (or equivalent)
+        if (wakeBeforePresent) {
+            thread->cond.wakeOne();
+            thread->mutex.unlock();
+        }
+    };
+
+    const QSize surfaceSize = m_sc->surfacePixelSize();
+    if (surfaceSize.isEmpty()) {
+        wakeUpIfNeeded();
+        return;
+    }
+
+    if (newlyExposed || m_sc->currentPixelSize() != surfaceSize)
         buildOrResizeSwapChain();
 
-    if (!m_hasSwapChain)
+    if (!m_hasSwapChain) {
+        wakeUpIfNeeded();
         return;
+    }
 
     QRhi::FrameOpResult result = r->beginFrame(m_sc);
     if (result == QRhi::FrameOpSwapChainOutOfDate) {
         buildOrResizeSwapChain();
-        if (!m_hasSwapChain)
+        if (!m_hasSwapChain) {
+            wakeUpIfNeeded();
             return;
+        }
         result = r->beginFrame(m_sc);
     }
-    if (result != QRhi::FrameOpSuccess)
+    if (result != QRhi::FrameOpSuccess) {
+        wakeUpIfNeeded();
         return;
+    }
 
     QRhiCommandBuffer *cb = m_sc->currentFrameCommandBuffer();
     const QSize outputSize = m_sc->currentPixelSize();
@@ -610,11 +630,7 @@ void Renderer::render(bool newlyExposed, bool wakeBeforePresent)
 
     cb->endPass();
 
-    // make sure the main/gui thread is not blocked when issuing the Present (or equivalent)
-    if (wakeBeforePresent) {
-        thread->cond.wakeOne();
-        thread->mutex.unlock();
-    }
+    wakeUpIfNeeded();
 
     r->endFrame(m_sc);
 }