Wave Slider
The Wave Slider displays the total progress made on that planet. It visualizes the mobs killed so far (green) and the remaining mobs (red) separated by a slider.
The slider is displayed using a LevelProgressBar class that extends the ProgressBar class from libGdx. The variable size for either side of the bar is achieved using a resizable rectangle created by getColoredDrawable.
The mechanism is carried out by the public ProgressBar (float min, float max, float stepSize, boolean vertical, ProgressBarStyle style) constructor, which continuously polls the mob count to update the bar as soon as a mob is killed.