//button callback example

var hit = false;

function setup() {

    createCanvas(1000,300);

}

​

function draw(){

    noStroke();

    rect(400,100,200,100);

​

    hit = collidePointRect(mouseX,mouseY,400,100,200,100); //see if the mouse is in the rect

​

    if(hit){ //change color!

        fill('purple')

    }else{

        fill('green')

    }

}

​