编辑器模式下焦点不在窗口内的卡顿

在 Windows 等平台上运行 UE 时在编辑器内 Play 游戏，若当前的焦点不在编辑器 /VR 应用内，会减少对 CPU 的占用，从而出现卡顿的问题 (打包出来不会出现这个问题)。
其实是因为 UE 在编辑器环境下做了不在焦点内的检测：

// Runtime/ApplicationCore/Private/Windows/WindowsPlatformApplicationMisc.cpp
void FWindowsPlatformApplicationMisc::PumpMessages(bool bFromMainLoop)
{
	if (!bFromMainLoop)
	{
		TGuardValue<bool> PumpMessageGuard(GPumpingMessagesOutsideOfMainLoop, true );
		// Process pending windows messages, which is necessary to the rendering thread in some rare cases where D3D
		// sends window messages (from IDXGISwapChain::Present) to the main thread owned viewport window.
		WinPumpSentMessages();
		return;
	}

	GPumpingMessagesOutsideOfMainLoop = false;
	WinPumpMessages();

	// Determine if application has focus
	bool HasFocus = FApp::UseVRFocus() ? FApp::HasVRFocus() : FWindowsPlatformApplicationMisc::IsThisApplicationForeground();

	// If editor thread doesn't have the focus, don't suck up too much CPU time.
	if(GIsEditor)
	{
		static bool HadFocus=1;
		if(HadFocus && !HasFocus)
		{
			// Drop our priority to speed up whatever is in the foreground.
			SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_BELOW_NORMAL);
		}
		else if(HasFocus && !HadFocus)
		{
			// Boost our priority back to normal.
			SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_NORMAL);
		}
		if(!HasFocus)
		{
			// Sleep for a bit to not eat up all CPU time.
			FPlatformProcess::Sleep(0.005f);
		}
		HadFocus = HasFocus;
	}
  // ...
}

只需要把 FPlatformProcess::Sleep(0.005f); 这一行注释掉就可以了。

这个需求是因为想要在非 DS 架构下多开在编辑器进行测试，因为不在焦点就会 sleep，所以会造成收发包的卡顿。