public void grayify() {
        for (int i = 0; i < gui.getBtnBuildings().size(); i++) {
            if (buildings.get(i).canBuyBuilding(hertz)) {
                gui.getBtnBuildings().get(i).setEnabled(true);
            } else {
                gui.getBtnBuildings().get(i).setEnabled(false);
            }
        }

        for (int i = 0; i < gui.getBtnUpgrades().size(); i++) {
            int upgOwned = upgrades.get(i).getOwned();
            int max = upgrades.get(i).getMaxOwned();
            int buildOwned = buildings.get(i).getOwned();

            if (upgrades.get(i).canBuyUpgrade(hertz) && buildOwned >= upgrades.get(i).getRequirement() && upgOwned < max) {
                gui.getBtnUpgrades().get(i).setEnabled(true);
            } else if (max == upgOwned) {
                gui.getBtnUpgrades().get(i).setEnabled(false);
            } else {
                gui.getBtnUpgrades().get(i).setEnabled(false);
            }
        }
        for (int i = 0; i < gui.getBtnAchievements().size(); i++) {
            if (achievements.get(i).getOwned()) {
                gui.getBtnAchievements().get(i).setEnabled(true);
            } else {
                gui.getBtnAchievements().get(i).setEnabled(false);
            }
        }
    }