size()
usage is quite limited: It can be used only once and it requires explicit values, no variables. So you need to think a bit differently. You can use displayWidth
to test display size and based on that set size like this.
void settings() {
if (displayWidth > 2000) {
size(2000,2000);
} else if(displayWidth < 1000) {
size(500,500);
} else {
size(1000,1000);
}
}