TimeHandler ever second with constricted Random Generator

Question

So

I have a method that gets called on every second to add sprites to a scene.

What i want to do is be able to control the percentage rate of which sprite gets added when the method is called.

So i tried using

Math.Random() > .3;

Basically this would be a 30% chance that the sprite would get added...correct?

So the problem with this was that i only have four sprites. So sometimes when the method was called no sprites would be added to the scene, when each time the method is called a sprite is added.

So tried using

    Random rand = new Random();

int itemNumber = rand.nextInt(4) + 1;

if (itemNumber == 1) {

The problem with this is this is totally controlled by the Random generator. When i want to be able to control the percentage of which sprite is added more or less.

So what would be my way of doing this??

Geobits Geobits · Accepted Answer · 2012-06-29T00:54:04

To start, this:

if(Math.Random() > .3)

will pass 70% of the time, not 30%. If you want 30%, change it to <

EDIT:

Ok, so you want to ensure a sprite is called, and want to be able to control how often each particular sprite is called? What you need is a variable for each sprite that contains the odds of calling it. For example, this will return an int to represent each sprite:

final double[] mOdds = {0.10, 0.25, 0.30, 0.35};   
// note, mOdds totals 1.0

public int pickSprite()
{
    double rand = Math.Random();
    for(int i=0;i<mOdds.length;i++)
    {
        if(rand < mOdds[i])
            return i;
        rand -= mOdds[i];
    }
    return -1;                    // should never reach this
}

You could use arbitrary numbers in your mOdds that don't add to 1.0, but you'd have to modify it a bit. Basically, you just have to make sure that rand will give you a number between 0 and the total of all the mOdds if you want a sprite every turn.

Update 2:

In your drawing routine, you can call the above function to choose the sprite and draw accordingly:

...
switch(pickSprite())
{
case 0:
    // draw sprite 0
    break;
case 1:
    // draw sprite 1
    break;
case 2:
    // draw sprite 2
    break;
case 3:
    // draw sprite 3
    break;
}
...

Or, if you have the sprites in an array, it's even easier:

...
sprite[pickSprite()].draw(); // substitute however you draw
...

It all depends on your program flow, really. You should be able to adapt the concept to whatever routine you're using.

TimeHandler ever second with constricted Random Generator

2 Answers