Orb images that come with ValHUD. In the settings window (F1), a bar section with Style = Orb has Orb: Back Image,
Orb: Liquid Image, Orb: Glass Image and Orb: Frame Image: press Choose next to any of them to pick from this folder,
or type a file name. Put your own PNGs here too and they appear in the list.

ValHUD set (generated by tools/orb-skin/make_orbs.py, no third-party art; free to use and modify)
  orb-back.png    empty orb, dark glass                 -> Orb: Back Image
  orb-fill.png    liquid in grey: Bar: Color tints it   -> Orb: Liquid Image (Tint Liquid Image on)
  orb-glass.png   highlights and rim shade              -> Orb: Glass Image
  orb-frame.png   bronze ring with rivets               -> Orb: Frame Image (Frame Size 1.25)

itsmars set: "Health Orb 1.1" by itsmars, CC0 (public domain), https://opengameart.org/content/health-orb-11
  itsmars_orb-back.png, itsmars_orb-back2.png, itsmars_orb_fill.png (white: Bar: Color tints it),
  itsmars_orb-glass.png, itsmars_orb-frame.png

DarthVladi frames (by the author of ValHUD)
  darthvladi_orb-frame.png, darthvladi_orb-frame_silver.png

The built-in layout "Orbs PNG" uses the itsmars back, fill and glass with the DarthVladi frames.

Making your own: square PNGs with transparency; 512 x 512 is plenty (210 x 210 works too). The liquid must fill its
picture edge to edge, because the level is measured on the whole picture. Any layer left empty is drawn by ValHUD.
