Random Sprite Speed

Question

I followed the Rain Catcher tutorial from libGDX and I made some modifications to the code, allowing the rain drops to appear faster. But I cant figure out how to make the raindrops fall at random speeds.

How can I make random raindrops fall at different speeds? I also want the raindrops to accelerate when it gets closer to the bottom.

Answer 1

The first thing to do, would be to specify a velocity component for the raindrop class; which specifies how fast the raindrop falls. To apply this, try the following (assuming the velocity component is called yVelocity):

// Take this line
raindrop.y -= 200 * Gdx.graphics.getDeltaTime();
// Replace with something like
raindrop.y -= raindrop.yVelocity * Gdx.graphics.getDeltaTime();

You can set the yVelocity in the constructor of the raindrop using the random function. (See here for an example of how to use the random function to get a value within a range).

If you want only specific random raindrops to have a random speed applied to then; use the random function to determine whether the constructed raindrop is allowed to have a random speed applied, by checking that the random value falls within a certain range.

The following example applies a random velocity to roughly 1 in 10 raindrops.

if (Math.random() >= 0.9) {
    raindrop.yVelocity = //Random velocity calculation here;
}
else {
    raindrop.yVelocity = 200;
}

To have the raindrops move faster as they travel down the screen, simply increase yVelocity by a gravitational constant in the update call for each raindrop. :)

EDIT: I would recommend that you made Raindrop a class of it's own, as using rectangle directly in that fashion severely restricts what properties you can apply to the raindrops.