ChangeWindowSize.pde

void setup(){
  size(500,500);
  
  surface.setResizable(true);
  //PSurface psf = getSurface();
  //psf.setResizable(true);
  
  
  frameRate(30);
  textAlign(CENTER,CENTER);
}

int PWidth = 500;
int PHeight = 500;
float ScaleW = 1.0;
float ScaleH = 1.0;
  
void draw() throws IllegalArgumentException{

  if(PWidth != width || PHeight!=height){
    ScaleW *= (float)width / PWidth;
    ScaleH *= (float)height / PHeight;
    PWidth = width;
    PHeight = height;
  }
  
  println(ScaleW,ScaleH);
  scale(ScaleW,ScaleH);
  
  background(0);
  noStroke();
  
  fill(0,255,0);
  ellipse(100,100,200,200);
  
  fill(255,255,0);
  rect(200,200,300,300);
  
  fill(255);
  textSize(48);
  text("W:" + PWidth,350,100);
  text("H:" + PHeight,100,350);

}