public void Upgrades()
{
// only if player has lives to spare
if (lives > 1)
{
// temporarily block keyboard inputs and pause
allowInputs = false;
upgrading = true;
Pause();
upgrades.SetActive(true);
heartsGUI.Display();
// randomly select available upgrades
button1.GetComponent <UpgradeButton>().LoadPowerUps();
button2.GetComponent <UpgradeButton>().LoadPowerUps();
}
}