How can i change background color in a while loop - processing - background

Question

I'm new to processing and trying to make a very simple program where i have an arduino that produces a seriel input (according to an analogue read value). The idea is a Processing window will open with a block color shown for 30 seconds. In this time all the readings from the arduino will be summed and averaged - creating an average for that color.
After 30 seconds the colour will change and a new average (for the next color) will start being calculated. This is the code i have started to write (for now focusing on just one 30 second period of green).
I realise there are likely problems with the reading/summing and averaging (i havent researched these yet so i'll put that to one side) - but my main question is why isn't the background green? When i run this program i expect the background to be green for 30 seconds - where as what happens is it is white for 30 seconds then changes to green. Can't figure out why! Thanks for any help!
import processing.serial.*;
Serial myPort;
float gsrAverage;
float greenAverage;
int gsrValue;
int greenTotal = 0;
int greenCount = 1;
int timeSinceStart = 0;
int timeAtStart;
int count=0;
color green = color(118,236,0);
void setup () {
size(900, 450);
// List all the available serial ports
//println(Serial.list());
myPort = new Serial(this, Serial.list()[0], 9600);
}
void draw () {
while (timeSinceStart < 30000) {
background(green);
greenTotal = greenTotal + gsrValue;
greenCount = greenCount + 1;
delay(500);
timeSinceStart = millis()-timeAtStart;
//println(timeSinceStart); for de bugging
}
greenAverage = greenTotal/greenCount;
//println(greenAverage); for de bugging
}
void serialEvent (Serial myPort) {
int inByte=myPort.read();
//0-255
gsrValue=inByte;
}

Answer 1

What I like to do for timers, is use IF statements and use millis() or a constantly updated variable 'm' right inside the condition:
int timeSinceStart;
int m;
void setup(){
timeSinceStart = millis(); // initialize here so it only happens once
}
void draw(){
m = millis(); // constantly update the variable
if(timeSinceStart + 30000 < m){
greenAverage = greenTotal/greenCount; // or whatever is outside while loop
timeSinceStart = millis();
}
//Anything that went inside the while loop can go here, or above the IF
}
This makes it so around every 30 seconds, the background will change once, and you just re-update the timeSinceStart variable in there too. This way, it will only update when you want it to update and not constantly update and break the code.
I tend not to use while loops in processing as they usually cause headaches. Hope my example helps.

Answer 2

May have found a way round this using an IF statement. I perhaps looked over the fact the draw function is itself a loop, so i was able to use a variation of
if (timeSinceStart < 5000) {
background(green);
}
within draw.

Answer 3

When dealing with timed events in Processing you should not use while loops inside the draw() function. The draw() function itself is a while loop which updates the "screen" each frame.
So, what you should do is create a timer and let it do a switch for you inside the draw() function. In your case, if you want to start with a green screen, you do that in the setup() function, and then create a method for altering according to a timer in your draw() function.
This is a suggestion on how you could solve your particular problem. Just change the cycle variable according to your need. In your case it would be 30000.
boolean isGreen = true;
int startTime = 0;
int lastTime = 0;
int cycle = 1000; //the cycle you need
void setup() {
size(200, 200);
background(0, 255, 0); //green
}
void draw() {
startTime = millis();
if (startTime > lastTime + cycle) {
if (isGreen) {
background(255); //white
isGreen = !isGreen;
} else {
background(0, 255, 0); //green
isGreen = !isGreen;
}
lastTime = millis();
}
}