mousePressed not updating in while loop

Processing Beginners
4

possibly you get a feeling about delay when play this:

/* start from example Basics / Input / Mouse Press.  */
boolean usedelay = false;

void setup() {
  size(200,200);
  background(200,200,0);
  println("use key [d] toggle delay 1 sec\nkey [c] clear");
}

void draw() {
  if (mousePressed)  stroke(255);
  else               stroke(0);
  circle(mouseX,mouseY,20);
  if ( usedelay ) delay(1000);
}

void keyPressed() {
 if ( key == 'd' ) {
   usedelay = ! usedelay;
   println("usedelay "+usedelay);
 }
 if ( key == 'c' ) background(200,200,0);      // clear
}

so again, you should not use delay!

but how to delay a action?
for this use must program a timer,
what you can not do as long you get the basic draw loop function wrong.

// add timer
long startT, delayT=5000;

/* start from example Basics / Input / Mouse Press.  */
boolean usedelay = false;

void setup() {
  size(200,200);
  background(200,200,0);
  println("use key [d] toggle delay 1 sec\nkey [c] clear");
}

void draw() {
  if (mousePressed)  stroke(255);
  else               stroke(0);
  circle(mouseX,mouseY,20);
  if ( usedelay ) delay(1000);
  myTimer();
}

void keyPressed() {
 if ( key == 'd' ) {
   usedelay = ! usedelay;
   println("usedelay "+usedelay);
 }
 if ( key == 'c' ) background(200,200,0);      // clear
}

void myTimer(){
  if ( millis() > startT + delayT ) {
   startT += delayT;                    // repeating timer
   println(" what happen now? auto clear ");
   background(200,200,0);
  }
}