Emulating the frame is also just part of the emulator. I.e. you got the display memory in some array (of pixel colors) in your code and the emulated instruction

Emulating the frame is also just part of the emulator. I.e. you got the display memory in some array (of pixel colors) in your code and the emulated instructions modify it. Then you just have to draw whatever is in that array on a "canvas" that your programming language supports.