Mouse Functions
Mousewheel = Cursor Z / Depth
CTRL + MouseWheel = Zoom
SHIFT + MouseWheel = Move Layer Z
ALT + LeftClick = Pickup Colour (from left image)
ALT + RightClick = Pickup Brush (from left image)
Middle Button = Snap to Layer Depth / Pickup Depth
Left Button = Draw with current tool
Right Button = Restore to original image (Magic Undo)