All sketches require a user defined [settings][settings] method. This is where you define the sketch size (can be fullscreen) and render mode. Regular processing sketches hide this in a pre-process step that converts pde code to valid java code (on linux you can find the java code in the /tmp folder, and in some other temporary location on MacOS and Windows).

Minimal code default renderer:-

def settings
  size 200, 200
end

Minimal code fullscreen default renderer:-

def settings
  fullscreen
end

Minimal code fullscreen opengl 3D renderer:-

def settings
  size 200, 200, P3D
end

Minimal code fullscreen opengl 3D renderer:-

def settings
  fullscreen P3D
end

For hi-dpi screens:-

def settings
  size 200, 200
  pixel_density(2)
end

You should also put smooth inside [settings][settings]

NB: as with vanilla-processing you can access the width and height variables within the sketch, eg in draw loop or mouse_pressed. [settings]:https://processing.org/reference/settings_.html