How to draw a black pixel on top of any application without a window?

Question

C++ / C#

I want to make an application that creates a black pixel in the center of the screen that could be displayed even on top of the on-screen keyboard or full-screen game. Is it possible to do this without creating a window?
Judging by the description of Hardware overlay, it can only be used in windowed mode and only by one application at a time, can I change the hdmi signal for example (so that the pixel is not visible during broadcast)?

Answer 1

Well, actually there are a couple of solutions

• Hook Nvidia Geforce Experience overlay. At the moment, no one has done this, but everything is ahead
  
• Draw on steam/origin/epicgames overlay. You can also draw on the discord overlay
  
• You can replace the driver, but that's too much
  
• Intercepting the rendering of the game itself