Hi all,
as the title already suggests I am experiencing an issue, where the unity process suddenly uses an excessive amount of CPU when I hide the game’s window.
This is my setup:
I develop a WPF application (the parent), with the unity game being just a child process of the main application. Therefor, when I start the game, I pass the CommandLine-Argument to the game process to embed the standalone playern in my main application (see Unity - Manual: Command-line arguments):
_gameProcess.StartInfo.CreateNoWindow = true;
_gameProcess.StartInfo.Arguments += "-parentHWND " + mainWindowHandle.ToInt32() + " " + Environment.CommandLine + " ";
So far everything works fine. But I also needed some pause/resume functionality without always quitting the game entirely. So my mechanism for halting the game is as follows:
- Parent sends a message to the game so that it pauses itself
- game will Load a blank scene and set the Time.timeScale to 0f.
- Parent hides the game window using calls to the User32.dll:
// in the wrapper for the User32.dll
internal const int SW_HIDE = 0;
internal const int SW_Show = 5;
[DllImport("user32.dll")]
internal static extern bool ShowWindow(IntPtr hwnd, int show);
// hiding the game
SendMessgeToGame("stop"); // Communication is done via Anonymous Pipes
User32.ShowWindow(_gameWindowHandle, User32.SW_HIDE);
Now comes the strange part:
At first, my game process used approximately 1.3% of CPU. After hiding the window it suddenly uses round about 30%. I already tried not hiding the game and just switching to the blank scene which will reduce the CPU usage to about 0.7%. Also, different ShowWindow-Flags like SW_Minimize and the like did not help either.
Did anyone of you experience this issue before? I am happy for every hint/opinion 
P.S.: If someone needs more detailed information let me know!
Edit:
I just tried the same mechanism with notepad++ being the child process. CPU usage stays unchanged, so my guess would be that this is an issue within Unity.