Display images alternately

Processing Beginners
1

How can I display an image in draw() successively with a delay between them?

PImage img1;
PImage img2;

void setup () {

  img1 = loadImage("step5.png");
  img2 = loadImage("fail2.png");
  size(801,583);  
  background(#B70F0F);  
  delay(2000);

}

void draw (){
  background(img1);
  delay(2000);
  background(img2);
  delay(2000);
}

When i run this it shows the background colour from setup() after 2 seconds, then it runs for 4 seconds and shows the secend image (img2). How can I just show an image and then another one? I need something similar for a project, where I want to show certain images when certain inputs come from a serial port. That works with console messages (println()), but if I let the program show images instead it runs to the end and only shows the last image.

2

If I use:

image(img1,0,0);

there is the same issue.

3

When I use rectangles instead of images there is also the same issue, so it has to be something wrong with my understanding of processing.

4

basically best is NOT to use

delay();

at all.

first for the understanding,
draw() should run 60 times per second
( show all what you want show at that moment / draw inside the whole draw() loop
and yes, does not matter if image / shape / primitive … )

if you want show different things / at a different time /
need a stage / timer concept /

a start timer code play with
Making a for loop ( or timer ) this