Note to self for later.

diff --git a/demos/demo_xcb.h b/demos/demo_xcb.h
index 5e4149852..6c59a8131 100644
--- a/demos/demo_xcb.h
+++ b/demos/demo_xcb.h
@@ -474,7 +474,9 @@ static inline ID3D12Resource *demo_swapchain_get_back_buffer(struct demo_swapcha
 
 static inline void demo_swapchain_present(struct demo_swapchain *swapchain)
 {
-    IDXGIVkSwapChain_Present(swapchain->swapchain, 1, 0, NULL);
+    static int counter;
+    counter++;
+    IDXGIVkSwapChain_Present(swapchain->swapchain, counter % 512 < 256 ? 1 : 0, 0, NULL);
     acquire_eventfd(swapchain->fd);
 }